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_reset_debug_ptr - reset the debug ptr to point to the vcpu state
  73  */
  74
  75 void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
  76 {
  77         vcpu->arch.debug_ptr = &vcpu->arch.vcpu_debug_state;
  78 }
  79
  80 /**
  81  * kvm_arm_setup_debug - set up debug related stuff
  82  *
  83  * @vcpu:       the vcpu pointer
  84  *
  85  * This is called before each entry into the hypervisor to setup any
  86  * debug related registers. Currently this just ensures we will trap
  87  * access to:
  88  *  - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR)
  89  *  - Debug ROM Address (MDCR_EL2_TDRA)
  90  *  - OS related registers (MDCR_EL2_TDOSA)
  91  *  - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB)
  92  *
  93  * Additionally, KVM only traps guest accesses to the debug registers if
  94  * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
  95  * flag on vcpu->arch.flags).  Since the guest must not interfere
  96  * with the hardware state when debugging the guest, we must ensure that
  97  * trapping is enabled whenever we are debugging the guest using the
  98  * debug registers.
  99  */
 100
 101 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
 102 {
 103         bool trap_debug = !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY);
 104         unsigned long mdscr, orig_mdcr_el2 = vcpu->arch.mdcr_el2;
 105
 106         trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
 107
 108         /*
 109          * This also clears MDCR_EL2_E2PB_MASK to disable guest access
 110          * to the profiling buffer.
 111          */
 112         vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
 113         vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
 114                                 MDCR_EL2_TPMS |
 115                                 MDCR_EL2_TPMCR |
 116                                 MDCR_EL2_TDRA |
 117                                 MDCR_EL2_TDOSA);
 118
 119         /* Is Guest debugging in effect? */
 120         if (vcpu->guest_debug) {
 121                 /* Route all software debug exceptions to EL2 */
 122                 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
 123
 124                 /* Save guest debug state */
 125                 save_guest_debug_regs(vcpu);
 126
 127                 /*
 128                  * Single Step (ARM ARM D2.12.3 The software step state
 129                  * machine)
 130                  *
 131                  * If we are doing Single Step we need to manipulate
 132                  * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the
 133                  * step has occurred the hypervisor will trap the
 134                  * debug exception and we return to userspace.
 135                  *
 136                  * If the guest attempts to single step its userspace
 137                  * we would have to deal with a trapped exception
 138                  * while in the guest kernel. Because this would be
 139                  * hard to unwind we suppress the guest's ability to
 140                  * do so by masking MDSCR_EL.SS.
 141                  *
 142                  * This confuses guest debuggers which use
 143                  * single-step behind the scenes but everything
 144                  * returns to normal once the host is no longer
 145                  * debugging the system.
 146                  */
 147                 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
 148                         *vcpu_cpsr(vcpu) |=  DBG_SPSR_SS;
 149                         mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
 150                         mdscr |= DBG_MDSCR_SS;
 151                         vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
 152                 } else {
 153                         mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
 154                         mdscr &= ~DBG_MDSCR_SS;
 155                         vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
 156                 }
 157
 158                 trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu));
 159
 160                 /*
 161                  * HW Breakpoints and watchpoints
 162                  *
 163                  * We simply switch the debug_ptr to point to our new
 164                  * external_debug_state which has been populated by the
 165                  * debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY
 166                  * mechanism ensures the registers are updated on the
 167                  * world switch.
 168                  */
 169                 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
 170                         /* Enable breakpoints/watchpoints */
 171                         mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
 172                         mdscr |= DBG_MDSCR_MDE;
 173                         vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
 174
 175                         vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
 176                         vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
 177                         trap_debug = true;
 178
 179                         trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
 180                                                 &vcpu->arch.debug_ptr->dbg_bcr[0],
 181                                                 &vcpu->arch.debug_ptr->dbg_bvr[0]);
 182
 183                         trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
 184                                                 &vcpu->arch.debug_ptr->dbg_wcr[0],
 185                                                 &vcpu->arch.debug_ptr->dbg_wvr[0]);
 186                 }
 187         }
 188
 189         BUG_ON(!vcpu->guest_debug &&
 190                 vcpu->arch.debug_ptr != &vcpu->arch.vcpu_debug_state);
 191
 192         /* Trap debug register access */
 193         if (trap_debug)
 194                 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
 195
 196         /* If KDE or MDE are set, perform a full save/restore cycle. */
 197         if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
 198                 vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
 199
 200         /* Write mdcr_el2 changes since vcpu_load on VHE systems */
 201         if (has_vhe() && orig_mdcr_el2 != vcpu->arch.mdcr_el2)
 202                 write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
 203
 204         trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
 205         trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));
 206 }
 207
 208 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
 209 {
 210         trace_kvm_arm_clear_debug(vcpu->guest_debug);
 211
 212         if (vcpu->guest_debug) {
 213                 restore_guest_debug_regs(vcpu);
 214
 215                 /*
 216                  * If we were using HW debug we need to restore the
 217                  * debug_ptr to the guest debug state.
 218                  */
 219                 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
 220                         kvm_arm_reset_debug_ptr(vcpu);
 221
 222                         trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
 223                                                 &vcpu->arch.debug_ptr->dbg_bcr[0],
 224                                                 &vcpu->arch.debug_ptr->dbg_bvr[0]);
 225
 226                         trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
 227                                                 &vcpu->arch.debug_ptr->dbg_wcr[0],
 228                                                 &vcpu->arch.debug_ptr->dbg_wvr[0]);
 229                 }
 230         }
 231 }