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[releases.git] / x86 / mm / tlb.c

// SPDX-License-Identifier: GPL-2.0-only
#include <linux/init.h>

#include <linux/mm.h>
#include <linux/spinlock.h>
#include <linux/smp.h>
#include <linux/interrupt.h>
#include <linux/export.h>
#include <linux/cpu.h>
#include <linux/debugfs.h>
#include <linux/sched/smt.h>
#include <linux/task_work.h>

#include <asm/tlbflush.h>
#include <asm/mmu_context.h>
#include <asm/nospec-branch.h>
#include <asm/cache.h>
#include <asm/cacheflush.h>
#include <asm/apic.h>
#include <asm/perf_event.h>

#include "mm_internal.h"

#ifdef CONFIG_PARAVIRT
# define STATIC_NOPV
#else
# define STATIC_NOPV                    static
# define __flush_tlb_local              native_flush_tlb_local
# define __flush_tlb_global             native_flush_tlb_global
# define __flush_tlb_one_user(addr)     native_flush_tlb_one_user(addr)
# define __flush_tlb_multi(msk, info)   native_flush_tlb_multi(msk, info)
#endif

/*
 *      TLB flushing, formerly SMP-only
 *              c/o Linus Torvalds.
 *
 *      These mean you can really definitely utterly forget about
 *      writing to user space from interrupts. (Its not allowed anyway).
 *
 *      Optimizations Manfred Spraul <manfred@colorfullife.com>
 *
 *      More scalable flush, from Andi Kleen
 *
 *      Implement flush IPI by CALL_FUNCTION_VECTOR, Alex Shi
 */

/*
 * Bits to mangle the TIF_SPEC_* state into the mm pointer which is
 * stored in cpu_tlb_state.last_user_mm_spec.
 */
#define LAST_USER_MM_IBPB       0x1UL
#define LAST_USER_MM_L1D_FLUSH  0x2UL
#define LAST_USER_MM_SPEC_MASK  (LAST_USER_MM_IBPB | LAST_USER_MM_L1D_FLUSH)

/* Bits to set when tlbstate and flush is (re)initialized */
#define LAST_USER_MM_INIT       LAST_USER_MM_IBPB

/*
 * The x86 feature is called PCID (Process Context IDentifier). It is similar
 * to what is traditionally called ASID on the RISC processors.
 *
 * We don't use the traditional ASID implementation, where each process/mm gets
 * its own ASID and flush/restart when we run out of ASID space.
 *
 * Instead we have a small per-cpu array of ASIDs and cache the last few mm's
 * that came by on this CPU, allowing cheaper switch_mm between processes on
 * this CPU.
 *
 * We end up with different spaces for different things. To avoid confusion we
 * use different names for each of them:
 *
 * ASID  - [0, TLB_NR_DYN_ASIDS-1]
 *         the canonical identifier for an mm
 *
 * kPCID - [1, TLB_NR_DYN_ASIDS]
 *         the value we write into the PCID part of CR3; corresponds to the
 *         ASID+1, because PCID 0 is special.
 *
 * uPCID - [2048 + 1, 2048 + TLB_NR_DYN_ASIDS]
 *         for KPTI each mm has two address spaces and thus needs two
 *         PCID values, but we can still do with a single ASID denomination
 *         for each mm. Corresponds to kPCID + 2048.
 *
 */

/* There are 12 bits of space for ASIDS in CR3 */
#define CR3_HW_ASID_BITS                12

/*
 * When enabled, PAGE_TABLE_ISOLATION consumes a single bit for
 * user/kernel switches
 */
#ifdef CONFIG_PAGE_TABLE_ISOLATION
# define PTI_CONSUMED_PCID_BITS 1
#else
# define PTI_CONSUMED_PCID_BITS 0
#endif

#define CR3_AVAIL_PCID_BITS (X86_CR3_PCID_BITS - PTI_CONSUMED_PCID_BITS)

/*
 * ASIDs are zero-based: 0->MAX_AVAIL_ASID are valid.  -1 below to account
 * for them being zero-based.  Another -1 is because PCID 0 is reserved for
 * use by non-PCID-aware users.
 */
#define MAX_ASID_AVAILABLE ((1 << CR3_AVAIL_PCID_BITS) - 2)

/*
 * Given @asid, compute kPCID
 */
static inline u16 kern_pcid(u16 asid)
{
        VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE);

#ifdef CONFIG_PAGE_TABLE_ISOLATION
        /*
         * Make sure that the dynamic ASID space does not conflict with the
         * bit we are using to switch between user and kernel ASIDs.
         */
        BUILD_BUG_ON(TLB_NR_DYN_ASIDS >= (1 << X86_CR3_PTI_PCID_USER_BIT));

        /*
         * The ASID being passed in here should have respected the
         * MAX_ASID_AVAILABLE and thus never have the switch bit set.
         */
        VM_WARN_ON_ONCE(asid & (1 << X86_CR3_PTI_PCID_USER_BIT));
#endif
        /*
         * The dynamically-assigned ASIDs that get passed in are small
         * (<TLB_NR_DYN_ASIDS).  They never have the high switch bit set,
         * so do not bother to clear it.
         *
         * If PCID is on, ASID-aware code paths put the ASID+1 into the
         * PCID bits.  This serves two purposes.  It prevents a nasty
         * situation in which PCID-unaware code saves CR3, loads some other
         * value (with PCID == 0), and then restores CR3, thus corrupting
         * the TLB for ASID 0 if the saved ASID was nonzero.  It also means
         * that any bugs involving loading a PCID-enabled CR3 with
         * CR4.PCIDE off will trigger deterministically.
         */
        return asid + 1;
}

/*
 * Given @asid, compute uPCID
 */
static inline u16 user_pcid(u16 asid)
{
        u16 ret = kern_pcid(asid);
#ifdef CONFIG_PAGE_TABLE_ISOLATION
        ret |= 1 << X86_CR3_PTI_PCID_USER_BIT;
#endif
        return ret;
}

static inline unsigned long build_cr3(pgd_t *pgd, u16 asid)
{
        if (static_cpu_has(X86_FEATURE_PCID)) {
                return __sme_pa(pgd) | kern_pcid(asid);
        } else {
                VM_WARN_ON_ONCE(asid != 0);
                return __sme_pa(pgd);
        }
}

static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid)
{
        VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE);
        /*
         * Use boot_cpu_has() instead of this_cpu_has() as this function
         * might be called during early boot. This should work even after
         * boot because all CPU's the have same capabilities:
         */
        VM_WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_PCID));
        return __sme_pa(pgd) | kern_pcid(asid) | CR3_NOFLUSH;
}

/*
 * We get here when we do something requiring a TLB invalidation
 * but could not go invalidate all of the contexts.  We do the
 * necessary invalidation by clearing out the 'ctx_id' which
 * forces a TLB flush when the context is loaded.
 */
static void clear_asid_other(void)
{
        u16 asid;

        /*
         * This is only expected to be set if we have disabled
         * kernel _PAGE_GLOBAL pages.
         */
        if (!static_cpu_has(X86_FEATURE_PTI)) {
                WARN_ON_ONCE(1);
                return;
        }

        for (asid = 0; asid < TLB_NR_DYN_ASIDS; asid++) {
                /* Do not need to flush the current asid */
                if (asid == this_cpu_read(cpu_tlbstate.loaded_mm_asid))
                        continue;
                /*
                 * Make sure the next time we go to switch to
                 * this asid, we do a flush:
                 */
                this_cpu_write(cpu_tlbstate.ctxs[asid].ctx_id, 0);
        }
        this_cpu_write(cpu_tlbstate.invalidate_other, false);
}

atomic64_t last_mm_ctx_id = ATOMIC64_INIT(1);


static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen,
                            u16 *new_asid, bool *need_flush)
{
        u16 asid;

        if (!static_cpu_has(X86_FEATURE_PCID)) {
                *new_asid = 0;
                *need_flush = true;
                return;
        }

        if (this_cpu_read(cpu_tlbstate.invalidate_other))
                clear_asid_other();

        for (asid = 0; asid < TLB_NR_DYN_ASIDS; asid++) {
                if (this_cpu_read(cpu_tlbstate.ctxs[asid].ctx_id) !=
                    next->context.ctx_id)
                        continue;

                *new_asid = asid;
                *need_flush = (this_cpu_read(cpu_tlbstate.ctxs[asid].tlb_gen) <
                               next_tlb_gen);
                return;
        }

        /*
         * We don't currently own an ASID slot on this CPU.
         * Allocate a slot.
         */
        *new_asid = this_cpu_add_return(cpu_tlbstate.next_asid, 1) - 1;
        if (*new_asid >= TLB_NR_DYN_ASIDS) {
                *new_asid = 0;
                this_cpu_write(cpu_tlbstate.next_asid, 1);
        }
        *need_flush = true;
}

/*
 * Given an ASID, flush the corresponding user ASID.  We can delay this
 * until the next time we switch to it.
 *
 * See SWITCH_TO_USER_CR3.
 */
static inline void invalidate_user_asid(u16 asid)
{
        /* There is no user ASID if address space separation is off */
        if (!IS_ENABLED(CONFIG_PAGE_TABLE_ISOLATION))
                return;

        /*
         * We only have a single ASID if PCID is off and the CR3
         * write will have flushed it.
         */
        if (!cpu_feature_enabled(X86_FEATURE_PCID))
                return;

        if (!static_cpu_has(X86_FEATURE_PTI))
                return;

        __set_bit(kern_pcid(asid),
                  (unsigned long *)this_cpu_ptr(&cpu_tlbstate.user_pcid_flush_mask));
}

static void load_new_mm_cr3(pgd_t *pgdir, u16 new_asid, bool need_flush)
{
        unsigned long new_mm_cr3;

        if (need_flush) {
                invalidate_user_asid(new_asid);
                new_mm_cr3 = build_cr3(pgdir, new_asid);
        } else {
                new_mm_cr3 = build_cr3_noflush(pgdir, new_asid);
        }

        /*
         * Caution: many callers of this function expect
         * that load_cr3() is serializing and orders TLB
         * fills with respect to the mm_cpumask writes.
         */
        write_cr3(new_mm_cr3);
}

void leave_mm(int cpu)
{
        struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);

        /*
         * It's plausible that we're in lazy TLB mode while our mm is init_mm.
         * If so, our callers still expect us to flush the TLB, but there
         * aren't any user TLB entries in init_mm to worry about.
         *
         * This needs to happen before any other sanity checks due to
         * intel_idle's shenanigans.
         */
        if (loaded_mm == &init_mm)
                return;

        /* Warn if we're not lazy. */
        WARN_ON(!this_cpu_read(cpu_tlbstate_shared.is_lazy));

        switch_mm(NULL, &init_mm, NULL);
}
EXPORT_SYMBOL_GPL(leave_mm);

void switch_mm(struct mm_struct *prev, struct mm_struct *next,
               struct task_struct *tsk)
{
        unsigned long flags;

        local_irq_save(flags);
        switch_mm_irqs_off(prev, next, tsk);
        local_irq_restore(flags);
}

/*
 * Invoked from return to user/guest by a task that opted-in to L1D
 * flushing but ended up running on an SMT enabled core due to wrong
 * affinity settings or CPU hotplug. This is part of the paranoid L1D flush
 * contract which this task requested.
 */
static void l1d_flush_force_sigbus(struct callback_head *ch)
{
        force_sig(SIGBUS);
}

static void l1d_flush_evaluate(unsigned long prev_mm, unsigned long next_mm,
                                struct task_struct *next)
{
        /* Flush L1D if the outgoing task requests it */
        if (prev_mm & LAST_USER_MM_L1D_FLUSH)
                wrmsrl(MSR_IA32_FLUSH_CMD, L1D_FLUSH);

        /* Check whether the incoming task opted in for L1D flush */
        if (likely(!(next_mm & LAST_USER_MM_L1D_FLUSH)))
                return;

        /*
         * Validate that it is not running on an SMT sibling as this would
         * make the excercise pointless because the siblings share L1D. If
         * it runs on a SMT sibling, notify it with SIGBUS on return to
         * user/guest
         */
        if (this_cpu_read(cpu_info.smt_active)) {
                clear_ti_thread_flag(&next->thread_info, TIF_SPEC_L1D_FLUSH);
                next->l1d_flush_kill.func = l1d_flush_force_sigbus;
                task_work_add(next, &next->l1d_flush_kill, TWA_RESUME);
        }
}

static unsigned long mm_mangle_tif_spec_bits(struct task_struct *next)
{
        unsigned long next_tif = read_task_thread_flags(next);
        unsigned long spec_bits = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_SPEC_MASK;

        /*
         * Ensure that the bit shift above works as expected and the two flags
         * end up in bit 0 and 1.
         */
        BUILD_BUG_ON(TIF_SPEC_L1D_FLUSH != TIF_SPEC_IB + 1);

        return (unsigned long)next->mm | spec_bits;
}

static void cond_mitigation(struct task_struct *next)
{
        unsigned long prev_mm, next_mm;

        if (!next || !next->mm)
                return;

        next_mm = mm_mangle_tif_spec_bits(next);
        prev_mm = this_cpu_read(cpu_tlbstate.last_user_mm_spec);

        /*
         * Avoid user/user BTB poisoning by flushing the branch predictor
         * when switching between processes. This stops one process from
         * doing Spectre-v2 attacks on another.
         *
         * Both, the conditional and the always IBPB mode use the mm
         * pointer to avoid the IBPB when switching between tasks of the
         * same process. Using the mm pointer instead of mm->context.ctx_id
         * opens a hypothetical hole vs. mm_struct reuse, which is more or
         * less impossible to control by an attacker. Aside of that it
         * would only affect the first schedule so the theoretically
         * exposed data is not really interesting.
         */
        if (static_branch_likely(&switch_mm_cond_ibpb)) {
                /*
                 * This is a bit more complex than the always mode because
                 * it has to handle two cases:
                 *
                 * 1) Switch from a user space task (potential attacker)
                 *    which has TIF_SPEC_IB set to a user space task
                 *    (potential victim) which has TIF_SPEC_IB not set.
                 *
                 * 2) Switch from a user space task (potential attacker)
                 *    which has TIF_SPEC_IB not set to a user space task
                 *    (potential victim) which has TIF_SPEC_IB set.
                 *
                 * This could be done by unconditionally issuing IBPB when
                 * a task which has TIF_SPEC_IB set is either scheduled in
                 * or out. Though that results in two flushes when:
                 *
                 * - the same user space task is scheduled out and later
                 *   scheduled in again and only a kernel thread ran in
                 *   between.
                 *
                 * - a user space task belonging to the same process is
                 *   scheduled in after a kernel thread ran in between
                 *
                 * - a user space task belonging to the same process is
                 *   scheduled in immediately.
                 *
                 * Optimize this with reasonably small overhead for the
                 * above cases. Mangle the TIF_SPEC_IB bit into the mm
                 * pointer of the incoming task which is stored in
                 * cpu_tlbstate.last_user_mm_spec for comparison.
                 *
                 * Issue IBPB only if the mm's are different and one or
                 * both have the IBPB bit set.
                 */
                if (next_mm != prev_mm &&
                    (next_mm | prev_mm) & LAST_USER_MM_IBPB)
                        indirect_branch_prediction_barrier();
        }

        if (static_branch_unlikely(&switch_mm_always_ibpb)) {
                /*
                 * Only flush when switching to a user space task with a
                 * different context than the user space task which ran
                 * last on this CPU.
                 */
                if ((prev_mm & ~LAST_USER_MM_SPEC_MASK) !=
                                        (unsigned long)next->mm)
                        indirect_branch_prediction_barrier();
        }

        if (static_branch_unlikely(&switch_mm_cond_l1d_flush)) {
                /*
                 * Flush L1D when the outgoing task requested it and/or
                 * check whether the incoming task requested L1D flushing
                 * and ended up on an SMT sibling.
                 */
                if (unlikely((prev_mm | next_mm) & LAST_USER_MM_L1D_FLUSH))
                        l1d_flush_evaluate(prev_mm, next_mm, next);
        }

        this_cpu_write(cpu_tlbstate.last_user_mm_spec, next_mm);
}

#ifdef CONFIG_PERF_EVENTS
static inline void cr4_update_pce_mm(struct mm_struct *mm)
{
        if (static_branch_unlikely(&rdpmc_always_available_key) ||
            (!static_branch_unlikely(&rdpmc_never_available_key) &&
             atomic_read(&mm->context.perf_rdpmc_allowed))) {
                /*
                 * Clear the existing dirty counters to
                 * prevent the leak for an RDPMC task.
                 */
                perf_clear_dirty_counters();
                cr4_set_bits_irqsoff(X86_CR4_PCE);
        } else
                cr4_clear_bits_irqsoff(X86_CR4_PCE);
}

void cr4_update_pce(void *ignored)
{
        cr4_update_pce_mm(this_cpu_read(cpu_tlbstate.loaded_mm));
}

#else
static inline void cr4_update_pce_mm(struct mm_struct *mm) { }
#endif

void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
                        struct task_struct *tsk)
{
        struct mm_struct *real_prev = this_cpu_read(cpu_tlbstate.loaded_mm);
        u16 prev_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);
        bool was_lazy = this_cpu_read(cpu_tlbstate_shared.is_lazy);
        unsigned cpu = smp_processor_id();
        u64 next_tlb_gen;
        bool need_flush;
        u16 new_asid;

        /*
         * NB: The scheduler will call us with prev == next when switching
         * from lazy TLB mode to normal mode if active_mm isn't changing.
         * When this happens, we don't assume that CR3 (and hence
         * cpu_tlbstate.loaded_mm) matches next.
         *
         * NB: leave_mm() calls us with prev == NULL and tsk == NULL.
         */

        /* We don't want flush_tlb_func() to run concurrently with us. */
        if (IS_ENABLED(CONFIG_PROVE_LOCKING))
                WARN_ON_ONCE(!irqs_disabled());

        /*
         * Verify that CR3 is what we think it is.  This will catch
         * hypothetical buggy code that directly switches to swapper_pg_dir
         * without going through leave_mm() / switch_mm_irqs_off() or that
         * does something like write_cr3(read_cr3_pa()).
         *
         * Only do this check if CONFIG_DEBUG_VM=y because __read_cr3()
         * isn't free.
         */
#ifdef CONFIG_DEBUG_VM
        if (WARN_ON_ONCE(__read_cr3() != build_cr3(real_prev->pgd, prev_asid))) {
                /*
                 * If we were to BUG here, we'd be very likely to kill
                 * the system so hard that we don't see the call trace.
                 * Try to recover instead by ignoring the error and doing
                 * a global flush to minimize the chance of corruption.
                 *
                 * (This is far from being a fully correct recovery.
                 *  Architecturally, the CPU could prefetch something
                 *  back into an incorrect ASID slot and leave it there
                 *  to cause trouble down the road.  It's better than
                 *  nothing, though.)
                 */
                __flush_tlb_all();
        }
#endif
        if (was_lazy)
                this_cpu_write(cpu_tlbstate_shared.is_lazy, false);

        /*
         * The membarrier system call requires a full memory barrier and
         * core serialization before returning to user-space, after
         * storing to rq->curr, when changing mm.  This is because
         * membarrier() sends IPIs to all CPUs that are in the target mm
         * to make them issue memory barriers.  However, if another CPU
         * switches to/from the target mm concurrently with
         * membarrier(), it can cause that CPU not to receive an IPI
         * when it really should issue a memory barrier.  Writing to CR3
         * provides that full memory barrier and core serializing
         * instruction.
         */
        if (real_prev == next) {
                VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[prev_asid].ctx_id) !=
                           next->context.ctx_id);

                /*
                 * Even in lazy TLB mode, the CPU should stay set in the
                 * mm_cpumask. The TLB shootdown code can figure out from
                 * cpu_tlbstate_shared.is_lazy whether or not to send an IPI.
                 */
                if (WARN_ON_ONCE(real_prev != &init_mm &&
                                 !cpumask_test_cpu(cpu, mm_cpumask(next))))
                        cpumask_set_cpu(cpu, mm_cpumask(next));

                /*
                 * If the CPU is not in lazy TLB mode, we are just switching
                 * from one thread in a process to another thread in the same
                 * process. No TLB flush required.
                 */
                if (!was_lazy)
                        return;

                /*
                 * Read the tlb_gen to check whether a flush is needed.
                 * If the TLB is up to date, just use it.
                 * The barrier synchronizes with the tlb_gen increment in
                 * the TLB shootdown code.
                 */
                smp_mb();
                next_tlb_gen = atomic64_read(&next->context.tlb_gen);
                if (this_cpu_read(cpu_tlbstate.ctxs[prev_asid].tlb_gen) ==
                                next_tlb_gen)
                        return;

                /*
                 * TLB contents went out of date while we were in lazy
                 * mode. Fall through to the TLB switching code below.
                 */
                new_asid = prev_asid;
                need_flush = true;
        } else {
                /*
                 * Apply process to process speculation vulnerability
                 * mitigations if applicable.
                 */
                cond_mitigation(tsk);

                /*
                 * Stop remote flushes for the previous mm.
                 * Skip kernel threads; we never send init_mm TLB flushing IPIs,
                 * but the bitmap manipulation can cause cache line contention.
                 */
                if (real_prev != &init_mm) {
                        VM_WARN_ON_ONCE(!cpumask_test_cpu(cpu,
                                                mm_cpumask(real_prev)));
                        cpumask_clear_cpu(cpu, mm_cpumask(real_prev));
                }

                /*
                 * Start remote flushes and then read tlb_gen.
                 */
                if (next != &init_mm)
                        cpumask_set_cpu(cpu, mm_cpumask(next));
                next_tlb_gen = atomic64_read(&next->context.tlb_gen);

                choose_new_asid(next, next_tlb_gen, &new_asid, &need_flush);

                /* Let nmi_uaccess_okay() know that we're changing CR3. */
                this_cpu_write(cpu_tlbstate.loaded_mm, LOADED_MM_SWITCHING);
                barrier();
        }

        if (need_flush) {
                this_cpu_write(cpu_tlbstate.ctxs[new_asid].ctx_id, next->context.ctx_id);
                this_cpu_write(cpu_tlbstate.ctxs[new_asid].tlb_gen, next_tlb_gen);
                load_new_mm_cr3(next->pgd, new_asid, true);

                trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL);
        } else {
                /* The new ASID is already up to date. */
                load_new_mm_cr3(next->pgd, new_asid, false);

                trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, 0);
        }

        /* Make sure we write CR3 before loaded_mm. */
        barrier();

        this_cpu_write(cpu_tlbstate.loaded_mm, next);
        this_cpu_write(cpu_tlbstate.loaded_mm_asid, new_asid);

        if (next != real_prev) {
                cr4_update_pce_mm(next);
                switch_ldt(real_prev, next);
        }
}

/*
 * Please ignore the name of this function.  It should be called
 * switch_to_kernel_thread().
 *
 * enter_lazy_tlb() is a hint from the scheduler that we are entering a
 * kernel thread or other context without an mm.  Acceptable implementations
 * include doing nothing whatsoever, switching to init_mm, or various clever
 * lazy tricks to try to minimize TLB flushes.
 *
 * The scheduler reserves the right to call enter_lazy_tlb() several times
 * in a row.  It will notify us that we're going back to a real mm by
 * calling switch_mm_irqs_off().
 */
void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
{
        if (this_cpu_read(cpu_tlbstate.loaded_mm) == &init_mm)
                return;

        this_cpu_write(cpu_tlbstate_shared.is_lazy, true);
}

/*
 * Call this when reinitializing a CPU.  It fixes the following potential
 * problems:
 *
 * - The ASID changed from what cpu_tlbstate thinks it is (most likely
 *   because the CPU was taken down and came back up with CR3's PCID
 *   bits clear.  CPU hotplug can do this.
 *
 * - The TLB contains junk in slots corresponding to inactive ASIDs.
 *
 * - The CPU went so far out to lunch that it may have missed a TLB
 *   flush.
 */
void initialize_tlbstate_and_flush(void)
{
        int i;
        struct mm_struct *mm = this_cpu_read(cpu_tlbstate.loaded_mm);
        u64 tlb_gen = atomic64_read(&init_mm.context.tlb_gen);
        unsigned long cr3 = __read_cr3();

        /* Assert that CR3 already references the right mm. */
        WARN_ON((cr3 & CR3_ADDR_MASK) != __pa(mm->pgd));

        /*
         * Assert that CR4.PCIDE is set if needed.  (CR4.PCIDE initialization
         * doesn't work like other CR4 bits because it can only be set from
         * long mode.)
         */
        WARN_ON(boot_cpu_has(X86_FEATURE_PCID) &&
                !(cr4_read_shadow() & X86_CR4_PCIDE));

        /* Force ASID 0 and force a TLB flush. */
        write_cr3(build_cr3(mm->pgd, 0));

        /* Reinitialize tlbstate. */
        this_cpu_write(cpu_tlbstate.last_user_mm_spec, LAST_USER_MM_INIT);
        this_cpu_write(cpu_tlbstate.loaded_mm_asid, 0);
        this_cpu_write(cpu_tlbstate.next_asid, 1);
        this_cpu_write(cpu_tlbstate.ctxs[0].ctx_id, mm->context.ctx_id);
        this_cpu_write(cpu_tlbstate.ctxs[0].tlb_gen, tlb_gen);

        for (i = 1; i < TLB_NR_DYN_ASIDS; i++)
                this_cpu_write(cpu_tlbstate.ctxs[i].ctx_id, 0);
}

/*
 * flush_tlb_func()'s memory ordering requirement is that any
 * TLB fills that happen after we flush the TLB are ordered after we
 * read active_mm's tlb_gen.  We don't need any explicit barriers
 * because all x86 flush operations are serializing and the
 * atomic64_read operation won't be reordered by the compiler.
 */
static void flush_tlb_func(void *info)
{
        /*
         * We have three different tlb_gen values in here.  They are:
         *
         * - mm_tlb_gen:     the latest generation.
         * - local_tlb_gen:  the generation that this CPU has already caught
         *                   up to.
         * - f->new_tlb_gen: the generation that the requester of the flush
         *                   wants us to catch up to.
         */
        const struct flush_tlb_info *f = info;
        struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
        u32 loaded_mm_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);
        u64 local_tlb_gen = this_cpu_read(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen);
        bool local = smp_processor_id() == f->initiating_cpu;
        unsigned long nr_invalidate = 0;
        u64 mm_tlb_gen;

        /* This code cannot presently handle being reentered. */
        VM_WARN_ON(!irqs_disabled());

        if (!local) {
                inc_irq_stat(irq_tlb_count);
                count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);

                /* Can only happen on remote CPUs */
                if (f->mm && f->mm != loaded_mm)
                        return;
        }

        if (unlikely(loaded_mm == &init_mm))
                return;

        VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[loaded_mm_asid].ctx_id) !=
                   loaded_mm->context.ctx_id);

        if (this_cpu_read(cpu_tlbstate_shared.is_lazy)) {
                /*
                 * We're in lazy mode.  We need to at least flush our
                 * paging-structure cache to avoid speculatively reading
                 * garbage into our TLB.  Since switching to init_mm is barely
                 * slower than a minimal flush, just switch to init_mm.
                 *
                 * This should be rare, with native_flush_tlb_multi() skipping
                 * IPIs to lazy TLB mode CPUs.
                 */
                switch_mm_irqs_off(NULL, &init_mm, NULL);
                return;
        }

        if (unlikely(f->new_tlb_gen != TLB_GENERATION_INVALID &&
                     f->new_tlb_gen <= local_tlb_gen)) {
                /*
                 * The TLB is already up to date in respect to f->new_tlb_gen.
                 * While the core might be still behind mm_tlb_gen, checking
                 * mm_tlb_gen unnecessarily would have negative caching effects
                 * so avoid it.
                 */
                return;
        }

        /*
         * Defer mm_tlb_gen reading as long as possible to avoid cache
         * contention.
         */
        mm_tlb_gen = atomic64_read(&loaded_mm->context.tlb_gen);

        if (unlikely(local_tlb_gen == mm_tlb_gen)) {
                /*
                 * There's nothing to do: we're already up to date.  This can
                 * happen if two concurrent flushes happen -- the first flush to
                 * be handled can catch us all the way up, leaving no work for
                 * the second flush.
                 */
                goto done;
        }

        WARN_ON_ONCE(local_tlb_gen > mm_tlb_gen);
        WARN_ON_ONCE(f->new_tlb_gen > mm_tlb_gen);

        /*
         * If we get to this point, we know that our TLB is out of date.
         * This does not strictly imply that we need to flush (it's
         * possible that f->new_tlb_gen <= local_tlb_gen), but we're
         * going to need to flush in the very near future, so we might
         * as well get it over with.
         *
         * The only question is whether to do a full or partial flush.
         *
         * We do a partial flush if requested and two extra conditions
         * are met:
         *
         * 1. f->new_tlb_gen == local_tlb_gen + 1.  We have an invariant that
         *    we've always done all needed flushes to catch up to
         *    local_tlb_gen.  If, for example, local_tlb_gen == 2 and
         *    f->new_tlb_gen == 3, then we know that the flush needed to bring
         *    us up to date for tlb_gen 3 is the partial flush we're
         *    processing.
         *
         *    As an example of why this check is needed, suppose that there
         *    are two concurrent flushes.  The first is a full flush that
         *    changes context.tlb_gen from 1 to 2.  The second is a partial
         *    flush that changes context.tlb_gen from 2 to 3.  If they get
         *    processed on this CPU in reverse order, we'll see
         *     local_tlb_gen == 1, mm_tlb_gen == 3, and end != TLB_FLUSH_ALL.
         *    If we were to use __flush_tlb_one_user() and set local_tlb_gen to
         *    3, we'd be break the invariant: we'd update local_tlb_gen above
         *    1 without the full flush that's needed for tlb_gen 2.
         *
         * 2. f->new_tlb_gen == mm_tlb_gen.  This is purely an optimization.
         *    Partial TLB flushes are not all that much cheaper than full TLB
         *    flushes, so it seems unlikely that it would be a performance win
         *    to do a partial flush if that won't bring our TLB fully up to
         *    date.  By doing a full flush instead, we can increase
         *    local_tlb_gen all the way to mm_tlb_gen and we can probably
         *    avoid another flush in the very near future.
         */
        if (f->end != TLB_FLUSH_ALL &&
            f->new_tlb_gen == local_tlb_gen + 1 &&
            f->new_tlb_gen == mm_tlb_gen) {
                /* Partial flush */
                unsigned long addr = f->start;

                /* Partial flush cannot have invalid generations */
                VM_WARN_ON(f->new_tlb_gen == TLB_GENERATION_INVALID);

                /* Partial flush must have valid mm */
                VM_WARN_ON(f->mm == NULL);

                nr_invalidate = (f->end - f->start) >> f->stride_shift;

                while (addr < f->end) {
                        flush_tlb_one_user(addr);
                        addr += 1UL << f->stride_shift;
                }
                if (local)
                        count_vm_tlb_events(NR_TLB_LOCAL_FLUSH_ONE, nr_invalidate);
        } else {
                /* Full flush. */
                nr_invalidate = TLB_FLUSH_ALL;

                flush_tlb_local();
                if (local)
                        count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
        }

        /* Both paths above update our state to mm_tlb_gen. */
        this_cpu_write(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen, mm_tlb_gen);

        /* Tracing is done in a unified manner to reduce the code size */
done:
        trace_tlb_flush(!local ? TLB_REMOTE_SHOOTDOWN :
                                (f->mm == NULL) ? TLB_LOCAL_SHOOTDOWN :
                                                  TLB_LOCAL_MM_SHOOTDOWN,
                        nr_invalidate);
}

static bool tlb_is_not_lazy(int cpu, void *data)
{
        return !per_cpu(cpu_tlbstate_shared.is_lazy, cpu);
}

DEFINE_PER_CPU_SHARED_ALIGNED(struct tlb_state_shared, cpu_tlbstate_shared);
EXPORT_PER_CPU_SYMBOL(cpu_tlbstate_shared);

STATIC_NOPV void native_flush_tlb_multi(const struct cpumask *cpumask,
                                         const struct flush_tlb_info *info)
{
        /*
         * Do accounting and tracing. Note that there are (and have always been)
         * cases in which a remote TLB flush will be traced, but eventually
         * would not happen.
         */
        count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
        if (info->end == TLB_FLUSH_ALL)
                trace_tlb_flush(TLB_REMOTE_SEND_IPI, TLB_FLUSH_ALL);
        else
                trace_tlb_flush(TLB_REMOTE_SEND_IPI,
                                (info->end - info->start) >> PAGE_SHIFT);

        /*
         * If no page tables were freed, we can skip sending IPIs to
         * CPUs in lazy TLB mode. They will flush the CPU themselves
         * at the next context switch.
         *
         * However, if page tables are getting freed, we need to send the
         * IPI everywhere, to prevent CPUs in lazy TLB mode from tripping
         * up on the new contents of what used to be page tables, while
         * doing a speculative memory access.
         */
        if (info->freed_tables)
                on_each_cpu_mask(cpumask, flush_tlb_func, (void *)info, true);
        else
                on_each_cpu_cond_mask(tlb_is_not_lazy, flush_tlb_func,
                                (void *)info, 1, cpumask);
}

void flush_tlb_multi(const struct cpumask *cpumask,
                      const struct flush_tlb_info *info)
{
        __flush_tlb_multi(cpumask, info);
}

/*
 * See Documentation/x86/tlb.rst for details.  We choose 33
 * because it is large enough to cover the vast majority (at
 * least 95%) of allocations, and is small enough that we are
 * confident it will not cause too much overhead.  Each single
 * flush is about 100 ns, so this caps the maximum overhead at
 * _about_ 3,000 ns.
 *
 * This is in units of pages.
 */
unsigned long tlb_single_page_flush_ceiling __read_mostly = 33;

static DEFINE_PER_CPU_SHARED_ALIGNED(struct flush_tlb_info, flush_tlb_info);

#ifdef CONFIG_DEBUG_VM
static DEFINE_PER_CPU(unsigned int, flush_tlb_info_idx);
#endif

static struct flush_tlb_info *get_flush_tlb_info(struct mm_struct *mm,
                        unsigned long start, unsigned long end,
                        unsigned int stride_shift, bool freed_tables,
                        u64 new_tlb_gen)
{
        struct flush_tlb_info *info = this_cpu_ptr(&flush_tlb_info);

#ifdef CONFIG_DEBUG_VM
        /*
         * Ensure that the following code is non-reentrant and flush_tlb_info
         * is not overwritten. This means no TLB flushing is initiated by
         * interrupt handlers and machine-check exception handlers.
         */
        BUG_ON(this_cpu_inc_return(flush_tlb_info_idx) != 1);
#endif

        info->start             = start;
        info->end               = end;
        info->mm                = mm;
        info->stride_shift      = stride_shift;
        info->freed_tables      = freed_tables;
        info->new_tlb_gen       = new_tlb_gen;
        info->initiating_cpu    = smp_processor_id();

        return info;
}

static void put_flush_tlb_info(void)
{
#ifdef CONFIG_DEBUG_VM
        /* Complete reentrancy prevention checks */
        barrier();
        this_cpu_dec(flush_tlb_info_idx);
#endif
}

void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
                                unsigned long end, unsigned int stride_shift,
                                bool freed_tables)
{
        struct flush_tlb_info *info;
        u64 new_tlb_gen;
        int cpu;

        cpu = get_cpu();

        /* Should we flush just the requested range? */
        if ((end == TLB_FLUSH_ALL) ||
            ((end - start) >> stride_shift) > tlb_single_page_flush_ceiling) {
                start = 0;
                end = TLB_FLUSH_ALL;
        }

        /* This is also a barrier that synchronizes with switch_mm(). */
        new_tlb_gen = inc_mm_tlb_gen(mm);

        info = get_flush_tlb_info(mm, start, end, stride_shift, freed_tables,
                                  new_tlb_gen);

        /*
         * flush_tlb_multi() is not optimized for the common case in which only
         * a local TLB flush is needed. Optimize this use-case by calling
         * flush_tlb_func_local() directly in this case.
         */
        if (cpumask_any_but(mm_cpumask(mm), cpu) < nr_cpu_ids) {
                flush_tlb_multi(mm_cpumask(mm), info);
        } else if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) {
                lockdep_assert_irqs_enabled();
                local_irq_disable();
                flush_tlb_func(info);
                local_irq_enable();
        }

        put_flush_tlb_info();
        put_cpu();
}


static void do_flush_tlb_all(void *info)
{
        count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
        __flush_tlb_all();
}

void flush_tlb_all(void)
{
        count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
        on_each_cpu(do_flush_tlb_all, NULL, 1);
}

static void do_kernel_range_flush(void *info)
{
        struct flush_tlb_info *f = info;
        unsigned long addr;

        /* flush range by one by one 'invlpg' */
        for (addr = f->start; addr < f->end; addr += PAGE_SIZE)
                flush_tlb_one_kernel(addr);
}

void flush_tlb_kernel_range(unsigned long start, unsigned long end)
{
        /* Balance as user space task's flush, a bit conservative */
        if (end == TLB_FLUSH_ALL ||
            (end - start) > tlb_single_page_flush_ceiling << PAGE_SHIFT) {
                on_each_cpu(do_flush_tlb_all, NULL, 1);
        } else {
                struct flush_tlb_info *info;

                preempt_disable();
                info = get_flush_tlb_info(NULL, start, end, 0, false,
                                          TLB_GENERATION_INVALID);

                on_each_cpu(do_kernel_range_flush, info, 1);

                put_flush_tlb_info();
                preempt_enable();
        }
}

/*
 * This can be used from process context to figure out what the value of
 * CR3 is without needing to do a (slow) __read_cr3().
 *
 * It's intended to be used for code like KVM that sneakily changes CR3
 * and needs to restore it.  It needs to be used very carefully.
 */
unsigned long __get_current_cr3_fast(void)
{
        unsigned long cr3 = build_cr3(this_cpu_read(cpu_tlbstate.loaded_mm)->pgd,
                this_cpu_read(cpu_tlbstate.loaded_mm_asid));

        /* For now, be very restrictive about when this can be called. */
        VM_WARN_ON(in_nmi() || preemptible());

        VM_BUG_ON(cr3 != __read_cr3());
        return cr3;
}
EXPORT_SYMBOL_GPL(__get_current_cr3_fast);

/*
 * Flush one page in the kernel mapping
 */
void flush_tlb_one_kernel(unsigned long addr)
{
        count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ONE);

        /*
         * If PTI is off, then __flush_tlb_one_user() is just INVLPG or its
         * paravirt equivalent.  Even with PCID, this is sufficient: we only
         * use PCID if we also use global PTEs for the kernel mapping, and
         * INVLPG flushes global translations across all address spaces.
         *
         * If PTI is on, then the kernel is mapped with non-global PTEs, and
         * __flush_tlb_one_user() will flush the given address for the current
         * kernel address space and for its usermode counterpart, but it does
         * not flush it for other address spaces.
         */
        flush_tlb_one_user(addr);

        if (!static_cpu_has(X86_FEATURE_PTI))
                return;

        /*
         * See above.  We need to propagate the flush to all other address
         * spaces.  In principle, we only need to propagate it to kernelmode
         * address spaces, but the extra bookkeeping we would need is not
         * worth it.
         */
        this_cpu_write(cpu_tlbstate.invalidate_other, true);
}

/*
 * Flush one page in the user mapping
 */
STATIC_NOPV void native_flush_tlb_one_user(unsigned long addr)
{
        u32 loaded_mm_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);

        asm volatile("invlpg (%0)" ::"r" (addr) : "memory");

        if (!static_cpu_has(X86_FEATURE_PTI))
                return;

        /*
         * Some platforms #GP if we call invpcid(type=1/2) before CR4.PCIDE=1.
         * Just use invalidate_user_asid() in case we are called early.
         */
        if (!this_cpu_has(X86_FEATURE_INVPCID_SINGLE))
                invalidate_user_asid(loaded_mm_asid);
        else
                invpcid_flush_one(user_pcid(loaded_mm_asid), addr);
}

void flush_tlb_one_user(unsigned long addr)
{
        __flush_tlb_one_user(addr);
}

/*
 * Flush everything
 */
STATIC_NOPV void native_flush_tlb_global(void)
{
        unsigned long flags;

        if (static_cpu_has(X86_FEATURE_INVPCID)) {
                /*
                 * Using INVPCID is considerably faster than a pair of writes
                 * to CR4 sandwiched inside an IRQ flag save/restore.
                 *
                 * Note, this works with CR4.PCIDE=0 or 1.
                 */
                invpcid_flush_all();
                return;
        }

        /*
         * Read-modify-write to CR4 - protect it from preemption and
         * from interrupts. (Use the raw variant because this code can
         * be called from deep inside debugging code.)
         */
        raw_local_irq_save(flags);

        __native_tlb_flush_global(this_cpu_read(cpu_tlbstate.cr4));

        raw_local_irq_restore(flags);
}

/*
 * Flush the entire current user mapping
 */
STATIC_NOPV void native_flush_tlb_local(void)
{
        /*
         * Preemption or interrupts must be disabled to protect the access
         * to the per CPU variable and to prevent being preempted between
         * read_cr3() and write_cr3().
         */
        WARN_ON_ONCE(preemptible());

        invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid));

        /* If current->mm == NULL then the read_cr3() "borrows" an mm */
        native_write_cr3(__native_read_cr3());
}

void flush_tlb_local(void)
{
        __flush_tlb_local();
}

/*
 * Flush everything
 */
void __flush_tlb_all(void)
{
        /*
         * This is to catch users with enabled preemption and the PGE feature
         * and don't trigger the warning in __native_flush_tlb().
         */
        VM_WARN_ON_ONCE(preemptible());

        if (boot_cpu_has(X86_FEATURE_PGE)) {
                __flush_tlb_global();
        } else {
                /*
                 * !PGE -> !PCID (setup_pcid()), thus every flush is total.
                 */
                flush_tlb_local();
        }
}
EXPORT_SYMBOL_GPL(__flush_tlb_all);

void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
{
        struct flush_tlb_info *info;

        int cpu = get_cpu();

        info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, 0, false,
                                  TLB_GENERATION_INVALID);
        /*
         * flush_tlb_multi() is not optimized for the common case in which only
         * a local TLB flush is needed. Optimize this use-case by calling
         * flush_tlb_func_local() directly in this case.
         */
        if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids) {
                flush_tlb_multi(&batch->cpumask, info);
        } else if (cpumask_test_cpu(cpu, &batch->cpumask)) {
                lockdep_assert_irqs_enabled();
                local_irq_disable();
                flush_tlb_func(info);
                local_irq_enable();
        }

        cpumask_clear(&batch->cpumask);

        put_flush_tlb_info();
        put_cpu();
}

/*
 * Blindly accessing user memory from NMI context can be dangerous
 * if we're in the middle of switching the current user task or
 * switching the loaded mm.  It can also be dangerous if we
 * interrupted some kernel code that was temporarily using a
 * different mm.
 */
bool nmi_uaccess_okay(void)
{
        struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
        struct mm_struct *current_mm = current->mm;

        VM_WARN_ON_ONCE(!loaded_mm);

        /*
         * The condition we want to check is
         * current_mm->pgd == __va(read_cr3_pa()).  This may be slow, though,
         * if we're running in a VM with shadow paging, and nmi_uaccess_okay()
         * is supposed to be reasonably fast.
         *
         * Instead, we check the almost equivalent but somewhat conservative
         * condition below, and we rely on the fact that switch_mm_irqs_off()
         * sets loaded_mm to LOADED_MM_SWITCHING before writing to CR3.
         */
        if (loaded_mm != current_mm)
                return false;

        VM_WARN_ON_ONCE(current_mm->pgd != __va(read_cr3_pa()));

        return true;
}

static ssize_t tlbflush_read_file(struct file *file, char __user *user_buf,
                             size_t count, loff_t *ppos)
{
        char buf[32];
        unsigned int len;

        len = sprintf(buf, "%ld\n", tlb_single_page_flush_ceiling);
        return simple_read_from_buffer(user_buf, count, ppos, buf, len);
}

static ssize_t tlbflush_write_file(struct file *file,
                 const char __user *user_buf, size_t count, loff_t *ppos)
{
        char buf[32];
        ssize_t len;
        int ceiling;

        len = min(count, sizeof(buf) - 1);
        if (copy_from_user(buf, user_buf, len))
                return -EFAULT;

        buf[len] = '\0';
        if (kstrtoint(buf, 0, &ceiling))
                return -EINVAL;

        if (ceiling < 0)
                return -EINVAL;

        tlb_single_page_flush_ceiling = ceiling;
        return count;
}

static const struct file_operations fops_tlbflush = {
        .read = tlbflush_read_file,
        .write = tlbflush_write_file,
        .llseek = default_llseek,
};

static int __init create_tlb_single_page_flush_ceiling(void)
{
        debugfs_create_file("tlb_single_page_flush_ceiling", S_IRUSR | S_IWUSR,
                            arch_debugfs_dir, NULL, &fops_tlbflush);
        return 0;
}
late_initcall(create_tlb_single_page_flush_ceiling);