arch/arm64/kvm/debug.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * Debug and Guest Debug support
   4  *
   5  * Copyright (C) 2015 - Linaro Ltd
   6  * Author: Alex Bennée <alex.bennee@linaro.org>
   7  */
   8
   9 #include <linux/kvm_host.h>
  10 #include <linux/hw_breakpoint.h>
  11
  12 #include <asm/debug-monitors.h>
  13 #include <asm/kvm_asm.h>
  14 #include <asm/kvm_arm.h>
  15 #include <asm/kvm_emulate.h>
  16
  17 #include "trace.h"
  18
  19 /* These are the bits of MDSCR_EL1 we may manipulate */
  20 #define MDSCR_EL1_DEBUG_MASK    (DBG_MDSCR_SS | \
  21                                 DBG_MDSCR_KDE | \
  22                                 DBG_MDSCR_MDE)
  23
  24 static DEFINE_PER_CPU(u32, mdcr_el2);
  25
  26 /**
  27  * save/restore_guest_debug_regs
  28  *
  29  * For some debug operations we need to tweak some guest registers. As
  30  * a result we need to save the state of those registers before we
  31  * make those modifications.
  32  *
  33  * Guest access to MDSCR_EL1 is trapped by the hypervisor and handled
  34  * after we have restored the preserved value to the main context.
  35  */
  36 static void save_guest_debug_regs(struct kvm_vcpu *vcpu)
  37 {
  38         u64 val = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
  39
  40         vcpu->arch.guest_debug_preserved.mdscr_el1 = val;
  41
  42         trace_kvm_arm_set_dreg32("Saved MDSCR_EL1",
  43                                 vcpu->arch.guest_debug_preserved.mdscr_el1);
  44 }
  45
  46 static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
  47 {
  48         u64 val = vcpu->arch.guest_debug_preserved.mdscr_el1;
  49
  50         vcpu_write_sys_reg(vcpu, val, MDSCR_EL1);
  51
  52         trace_kvm_arm_set_dreg32("Restored MDSCR_EL1",
  53                                 vcpu_read_sys_reg(vcpu, MDSCR_EL1));
  54 }
  55
  56 /**
  57  * kvm_arm_init_debug - grab what we need for debug
  58  *
  59  * Currently the sole task of this function is to retrieve the initial
  60  * value of mdcr_el2 so we can preserve MDCR_EL2.HPMN which has
  61  * presumably been set-up by some knowledgeable bootcode.
  62  *
  63  * It is called once per-cpu during CPU hyp initialisation.
  64  */
  65
  66 void kvm_arm_init_debug(void)
  67 {
  68         __this_cpu_write(mdcr_el2, kvm_call_hyp_ret(__kvm_get_mdcr_el2));
  69 }
  70
  71 /**
  72  * kvm_arm_setup_mdcr_el2 - configure vcpu mdcr_el2 value
  73  *
  74  * @vcpu:       the vcpu pointer
  75  *
  76  * This ensures we will trap access to:
  77  *  - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR)
  78  *  - Debug ROM Address (MDCR_EL2_TDRA)
  79  *  - OS related registers (MDCR_EL2_TDOSA)
  80  *  - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB)
  81  *  - Self-hosted Trace Filter controls (MDCR_EL2_TTRF)
  82  */
  83 static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu)
  84 {
  85         /*
  86          * This also clears MDCR_EL2_E2PB_MASK to disable guest access
  87          * to the profiling buffer.
  88          */
  89         vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
  90         vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
  91                                 MDCR_EL2_TPMS |
  92                                 MDCR_EL2_TTRF |
  93                                 MDCR_EL2_TPMCR |
  94                                 MDCR_EL2_TDRA |
  95                                 MDCR_EL2_TDOSA);
  96
  97         /* Is the VM being debugged by userspace? */
  98         if (vcpu->guest_debug)
  99                 /* Route all software debug exceptions to EL2 */
 100                 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
 101
 102         /*
 103          * Trap debug register access when one of the following is true:
 104          *  - Userspace is using the hardware to debug the guest
 105          *  (KVM_GUESTDBG_USE_HW is set).
 106          *  - The guest is not using debug (KVM_ARM64_DEBUG_DIRTY is clear).
 107          */
 108         if ((vcpu->guest_debug & KVM_GUESTDBG_USE_HW) ||
 109             !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY))
 110                 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
 111
 112         trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
 113 }
 114
 115 /**
 116  * kvm_arm_vcpu_init_debug - setup vcpu debug traps
 117  *
 118  * @vcpu:       the vcpu pointer
 119  *
 120  * Set vcpu initial mdcr_el2 value.
 121  */
 122 void kvm_arm_vcpu_init_debug(struct kvm_vcpu *vcpu)
 123 {
 124         preempt_disable();
 125         kvm_arm_setup_mdcr_el2(vcpu);
 126         preempt_enable();
 127 }
 128
 129 /**
 130  * kvm_arm_reset_debug_ptr - reset the debug ptr to point to the vcpu state
 131  */
 132
 133 void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
 134 {
 135         vcpu->arch.debug_ptr = &vcpu->arch.vcpu_debug_state;
 136 }
 137
 138 /**
 139  * kvm_arm_setup_debug - set up debug related stuff
 140  *
 141  * @vcpu:       the vcpu pointer
 142  *
 143  * This is called before each entry into the hypervisor to setup any
 144  * debug related registers.
 145  *
 146  * Additionally, KVM only traps guest accesses to the debug registers if
 147  * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
 148  * flag on vcpu->arch.flags).  Since the guest must not interfere
 149  * with the hardware state when debugging the guest, we must ensure that
 150  * trapping is enabled whenever we are debugging the guest using the
 151  * debug registers.
 152  */
 153
 154 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
 155 {
 156         unsigned long mdscr, orig_mdcr_el2 = vcpu->arch.mdcr_el2;
 157
 158         trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
 159
 160         kvm_arm_setup_mdcr_el2(vcpu);
 161
 162         /* Is Guest debugging in effect? */
 163         if (vcpu->guest_debug) {
 164                 /* Save guest debug state */
 165                 save_guest_debug_regs(vcpu);
 166
 167                 /*
 168                  * Single Step (ARM ARM D2.12.3 The software step state
 169                  * machine)
 170                  *
 171                  * If we are doing Single Step we need to manipulate
 172                  * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the
 173                  * step has occurred the hypervisor will trap the
 174                  * debug exception and we return to userspace.
 175                  *
 176                  * If the guest attempts to single step its userspace
 177                  * we would have to deal with a trapped exception
 178                  * while in the guest kernel. Because this would be
 179                  * hard to unwind we suppress the guest's ability to
 180                  * do so by masking MDSCR_EL.SS.
 181                  *
 182                  * This confuses guest debuggers which use
 183                  * single-step behind the scenes but everything
 184                  * returns to normal once the host is no longer
 185                  * debugging the system.
 186                  */
 187                 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
 188                         *vcpu_cpsr(vcpu) |=  DBG_SPSR_SS;
 189                         mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
 190                         mdscr |= DBG_MDSCR_SS;
 191                         vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
 192                 } else {
 193                         mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
 194                         mdscr &= ~DBG_MDSCR_SS;
 195                         vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
 196                 }
 197
 198                 trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu));
 199
 200                 /*
 201                  * HW Breakpoints and watchpoints
 202                  *
 203                  * We simply switch the debug_ptr to point to our new
 204                  * external_debug_state which has been populated by the
 205                  * debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY
 206                  * mechanism ensures the registers are updated on the
 207                  * world switch.
 208                  */
 209                 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
 210                         /* Enable breakpoints/watchpoints */
 211                         mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
 212                         mdscr |= DBG_MDSCR_MDE;
 213                         vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
 214
 215                         vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
 216                         vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
 217
 218                         trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
 219                                                 &vcpu->arch.debug_ptr->dbg_bcr[0],
 220                                                 &vcpu->arch.debug_ptr->dbg_bvr[0]);
 221
 222                         trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
 223                                                 &vcpu->arch.debug_ptr->dbg_wcr[0],
 224                                                 &vcpu->arch.debug_ptr->dbg_wvr[0]);
 225                 }
 226         }
 227
 228         BUG_ON(!vcpu->guest_debug &&
 229                 vcpu->arch.debug_ptr != &vcpu->arch.vcpu_debug_state);
 230
 231         /* If KDE or MDE are set, perform a full save/restore cycle. */
 232         if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
 233                 vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
 234
 235         /* Write mdcr_el2 changes since vcpu_load on VHE systems */
 236         if (has_vhe() && orig_mdcr_el2 != vcpu->arch.mdcr_el2)
 237                 write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
 238
 239         trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));
 240 }
 241
 242 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
 243 {
 244         trace_kvm_arm_clear_debug(vcpu->guest_debug);
 245
 246         if (vcpu->guest_debug) {
 247                 restore_guest_debug_regs(vcpu);
 248
 249                 /*
 250                  * If we were using HW debug we need to restore the
 251                  * debug_ptr to the guest debug state.
 252                  */
 253                 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
 254                         kvm_arm_reset_debug_ptr(vcpu);
 255
 256                         trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
 257                                                 &vcpu->arch.debug_ptr->dbg_bcr[0],
 258                                                 &vcpu->arch.debug_ptr->dbg_bvr[0]);
 259
 260                         trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
 261                                                 &vcpu->arch.debug_ptr->dbg_wcr[0],
 262                                                 &vcpu->arch.debug_ptr->dbg_wvr[0]);
 263                 }
 264         }
 265 }