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(u64, 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  *  - Self-hosted Trace (MDCR_EL2_TTRF/MDCR_EL2_E2TB)
  83  */
  84 static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu)
  85 {
  86         /*
  87          * This also clears MDCR_EL2_E2PB_MASK and MDCR_EL2_E2TB_MASK
  88          * to disable guest access to the profiling and trace buffers
  89          */
  90         vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
  91         vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
  92                                 MDCR_EL2_TPMS |
  93                                 MDCR_EL2_TTRF |
  94                                 MDCR_EL2_TPMCR |
  95                                 MDCR_EL2_TDRA |
  96                                 MDCR_EL2_TDOSA);
  97
  98         /* Is the VM being debugged by userspace? */
  99         if (vcpu->guest_debug)
 100                 /* Route all software debug exceptions to EL2 */
 101                 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
 102
 103         /*
 104          * Trap debug register access when one of the following is true:
 105          *  - Userspace is using the hardware to debug the guest
 106          *  (KVM_GUESTDBG_USE_HW is set).
 107          *  - The guest is not using debug (KVM_ARM64_DEBUG_DIRTY is clear).
 108          */
 109         if ((vcpu->guest_debug & KVM_GUESTDBG_USE_HW) ||
 110             !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY))
 111                 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
 112
 113         trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
 114 }
 115
 116 /**
 117  * kvm_arm_vcpu_init_debug - setup vcpu debug traps
 118  *
 119  * @vcpu:       the vcpu pointer
 120  *
 121  * Set vcpu initial mdcr_el2 value.
 122  */
 123 void kvm_arm_vcpu_init_debug(struct kvm_vcpu *vcpu)
 124 {
 125         preempt_disable();
 126         kvm_arm_setup_mdcr_el2(vcpu);
 127         preempt_enable();
 128 }
 129
 130 /**
 131  * kvm_arm_reset_debug_ptr - reset the debug ptr to point to the vcpu state
 132  */
 133
 134 void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
 135 {
 136         vcpu->arch.debug_ptr = &vcpu->arch.vcpu_debug_state;
 137 }
 138
 139 /**
 140  * kvm_arm_setup_debug - set up debug related stuff
 141  *
 142  * @vcpu:       the vcpu pointer
 143  *
 144  * This is called before each entry into the hypervisor to setup any
 145  * debug related registers.
 146  *
 147  * Additionally, KVM only traps guest accesses to the debug registers if
 148  * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
 149  * flag on vcpu->arch.flags).  Since the guest must not interfere
 150  * with the hardware state when debugging the guest, we must ensure that
 151  * trapping is enabled whenever we are debugging the guest using the
 152  * debug registers.
 153  */
 154
 155 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
 156 {
 157         unsigned long mdscr, orig_mdcr_el2 = vcpu->arch.mdcr_el2;
 158
 159         trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
 160
 161         kvm_arm_setup_mdcr_el2(vcpu);
 162
 163         /* Is Guest debugging in effect? */
 164         if (vcpu->guest_debug) {
 165                 /* Save guest debug state */
 166                 save_guest_debug_regs(vcpu);
 167
 168                 /*
 169                  * Single Step (ARM ARM D2.12.3 The software step state
 170                  * machine)
 171                  *
 172                  * If we are doing Single Step we need to manipulate
 173                  * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the
 174                  * step has occurred the hypervisor will trap the
 175                  * debug exception and we return to userspace.
 176                  *
 177                  * If the guest attempts to single step its userspace
 178                  * we would have to deal with a trapped exception
 179                  * while in the guest kernel. Because this would be
 180                  * hard to unwind we suppress the guest's ability to
 181                  * do so by masking MDSCR_EL.SS.
 182                  *
 183                  * This confuses guest debuggers which use
 184                  * single-step behind the scenes but everything
 185                  * returns to normal once the host is no longer
 186                  * debugging the system.
 187                  */
 188                 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
 189                         *vcpu_cpsr(vcpu) |=  DBG_SPSR_SS;
 190                         mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
 191                         mdscr |= DBG_MDSCR_SS;
 192                         vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
 193                 } else {
 194                         mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
 195                         mdscr &= ~DBG_MDSCR_SS;
 196                         vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
 197                 }
 198
 199                 trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu));
 200
 201                 /*
 202                  * HW Breakpoints and watchpoints
 203                  *
 204                  * We simply switch the debug_ptr to point to our new
 205                  * external_debug_state which has been populated by the
 206                  * debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY
 207                  * mechanism ensures the registers are updated on the
 208                  * world switch.
 209                  */
 210                 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
 211                         /* Enable breakpoints/watchpoints */
 212                         mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
 213                         mdscr |= DBG_MDSCR_MDE;
 214                         vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
 215
 216                         vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
 217                         vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
 218
 219                         trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
 220                                                 &vcpu->arch.debug_ptr->dbg_bcr[0],
 221                                                 &vcpu->arch.debug_ptr->dbg_bvr[0]);
 222
 223                         trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
 224                                                 &vcpu->arch.debug_ptr->dbg_wcr[0],
 225                                                 &vcpu->arch.debug_ptr->dbg_wvr[0]);
 226                 }
 227         }
 228
 229         BUG_ON(!vcpu->guest_debug &&
 230                 vcpu->arch.debug_ptr != &vcpu->arch.vcpu_debug_state);
 231
 232         /* If KDE or MDE are set, perform a full save/restore cycle. */
 233         if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
 234                 vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
 235
 236         /* Write mdcr_el2 changes since vcpu_load on VHE systems */
 237         if (has_vhe() && orig_mdcr_el2 != vcpu->arch.mdcr_el2)
 238                 write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
 239
 240         trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));
 241 }
 242
 243 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
 244 {
 245         trace_kvm_arm_clear_debug(vcpu->guest_debug);
 246
 247         if (vcpu->guest_debug) {
 248                 restore_guest_debug_regs(vcpu);
 249
 250                 /*
 251                  * If we were using HW debug we need to restore the
 252                  * debug_ptr to the guest debug state.
 253                  */
 254                 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
 255                         kvm_arm_reset_debug_ptr(vcpu);
 256
 257                         trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
 258                                                 &vcpu->arch.debug_ptr->dbg_bcr[0],
 259                                                 &vcpu->arch.debug_ptr->dbg_bvr[0]);
 260
 261                         trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
 262                                                 &vcpu->arch.debug_ptr->dbg_wcr[0],
 263                                                 &vcpu->arch.debug_ptr->dbg_wvr[0]);
 264                 }
 265         }
 266 }
 267
 268 void kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu *vcpu)
 269 {
 270         u64 dfr0;
 271
 272         /* For VHE, there is nothing to do */
 273         if (has_vhe())
 274                 return;
 275
 276         dfr0 = read_sysreg(id_aa64dfr0_el1);
 277         /*
 278          * If SPE is present on this CPU and is available at current EL,
 279          * we may need to check if the host state needs to be saved.
 280          */
 281         if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_PMSVER_SHIFT) &&
 282             !(read_sysreg_s(SYS_PMBIDR_EL1) & BIT(SYS_PMBIDR_EL1_P_SHIFT)))
 283                 vcpu->arch.flags |= KVM_ARM64_DEBUG_STATE_SAVE_SPE;
 284
 285         /* Check if we have TRBE implemented and available at the host */
 286         if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_TRBE_SHIFT) &&
 287             !(read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_PROG))
 288                 vcpu->arch.flags |= KVM_ARM64_DEBUG_STATE_SAVE_TRBE;
 289 }
 290
 291 void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu)
 292 {
 293         vcpu->arch.flags &= ~(KVM_ARM64_DEBUG_STATE_SAVE_SPE |
 294                               KVM_ARM64_DEBUG_STATE_SAVE_TRBE);
 295 }