arch/arm64/kvm/debug.c

   1 /*
   2  * Debug and Guest Debug support
   3  *
   4  * Copyright (C) 2015 - Linaro Ltd
   5  * Author: Alex Bennée <alex.bennee@linaro.org>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14  * GNU General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18  */
  19
  20 #include <linux/kvm_host.h>
  21 #include <linux/hw_breakpoint.h>
  22
  23 #include <asm/debug-monitors.h>
  24 #include <asm/kvm_asm.h>
  25 #include <asm/kvm_arm.h>
  26 #include <asm/kvm_emulate.h>
  27
  28 #include "trace.h"
  29
  30 /* These are the bits of MDSCR_EL1 we may manipulate */
  31 #define MDSCR_EL1_DEBUG_MASK    (DBG_MDSCR_SS | \
  32                                 DBG_MDSCR_KDE | \
  33                                 DBG_MDSCR_MDE)
  34
  35 static DEFINE_PER_CPU(u32, mdcr_el2);
  36
  37 /**
  38  * save/restore_guest_debug_regs
  39  *
  40  * For some debug operations we need to tweak some guest registers. As
  41  * a result we need to save the state of those registers before we
  42  * make those modifications.
  43  *
  44  * Guest access to MDSCR_EL1 is trapped by the hypervisor and handled
  45  * after we have restored the preserved value to the main context.
  46  */
  47 static void save_guest_debug_regs(struct kvm_vcpu *vcpu)
  48 {
  49         vcpu->arch.guest_debug_preserved.mdscr_el1 = vcpu_sys_reg(vcpu, MDSCR_EL1);
  50
  51         trace_kvm_arm_set_dreg32("Saved MDSCR_EL1",
  52                                 vcpu->arch.guest_debug_preserved.mdscr_el1);
  53 }
  54
  55 static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
  56 {
  57         vcpu_sys_reg(vcpu, MDSCR_EL1) = vcpu->arch.guest_debug_preserved.mdscr_el1;
  58
  59         trace_kvm_arm_set_dreg32("Restored MDSCR_EL1",
  60                                 vcpu_sys_reg(vcpu, MDSCR_EL1));
  61 }
  62
  63 /**
  64  * kvm_arm_init_debug - grab what we need for debug
  65  *
  66  * Currently the sole task of this function is to retrieve the initial
  67  * value of mdcr_el2 so we can preserve MDCR_EL2.HPMN which has
  68  * presumably been set-up by some knowledgeable bootcode.
  69  *
  70  * It is called once per-cpu during CPU hyp initialisation.
  71  */
  72
  73 void kvm_arm_init_debug(void)
  74 {
  75         __this_cpu_write(mdcr_el2, kvm_call_hyp(__kvm_get_mdcr_el2));
  76 }
  77
  78 /**
  79  * kvm_arm_reset_debug_ptr - reset the debug ptr to point to the vcpu state
  80  */
  81
  82 void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
  83 {
  84         vcpu->arch.debug_ptr = &vcpu->arch.vcpu_debug_state;
  85 }
  86
  87 /**
  88  * kvm_arm_setup_debug - set up debug related stuff
  89  *
  90  * @vcpu:       the vcpu pointer
  91  *
  92  * This is called before each entry into the hypervisor to setup any
  93  * debug related registers. Currently this just ensures we will trap
  94  * access to:
  95  *  - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR)
  96  *  - Debug ROM Address (MDCR_EL2_TDRA)
  97  *  - OS related registers (MDCR_EL2_TDOSA)
  98  *  - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB)
  99  *
 100  * Additionally, KVM only traps guest accesses to the debug registers if
 101  * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
 102  * flag on vcpu->arch.debug_flags).  Since the guest must not interfere
 103  * with the hardware state when debugging the guest, we must ensure that
 104  * trapping is enabled whenever we are debugging the guest using the
 105  * debug registers.
 106  */
 107
 108 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
 109 {
 110         bool trap_debug = !(vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY);
 111
 112         trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
 113
 114         /*
 115          * This also clears MDCR_EL2_E2PB_MASK to disable guest access
 116          * to the profiling buffer.
 117          */
 118         vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
 119         vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
 120                                 MDCR_EL2_TPMS |
 121                                 MDCR_EL2_TPMCR |
 122                                 MDCR_EL2_TDRA |
 123                                 MDCR_EL2_TDOSA);
 124
 125         /* Is Guest debugging in effect? */
 126         if (vcpu->guest_debug) {
 127                 /* Route all software debug exceptions to EL2 */
 128                 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
 129
 130                 /* Save guest debug state */
 131                 save_guest_debug_regs(vcpu);
 132
 133                 /*
 134                  * Single Step (ARM ARM D2.12.3 The software step state
 135                  * machine)
 136                  *
 137                  * If we are doing Single Step we need to manipulate
 138                  * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the
 139                  * step has occurred the hypervisor will trap the
 140                  * debug exception and we return to userspace.
 141                  *
 142                  * If the guest attempts to single step its userspace
 143                  * we would have to deal with a trapped exception
 144                  * while in the guest kernel. Because this would be
 145                  * hard to unwind we suppress the guest's ability to
 146                  * do so by masking MDSCR_EL.SS.
 147                  *
 148                  * This confuses guest debuggers which use
 149                  * single-step behind the scenes but everything
 150                  * returns to normal once the host is no longer
 151                  * debugging the system.
 152                  */
 153                 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
 154                         *vcpu_cpsr(vcpu) |=  DBG_SPSR_SS;
 155                         vcpu_sys_reg(vcpu, MDSCR_EL1) |= DBG_MDSCR_SS;
 156                 } else {
 157                         vcpu_sys_reg(vcpu, MDSCR_EL1) &= ~DBG_MDSCR_SS;
 158                 }
 159
 160                 trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu));
 161
 162                 /*
 163                  * HW Breakpoints and watchpoints
 164                  *
 165                  * We simply switch the debug_ptr to point to our new
 166                  * external_debug_state which has been populated by the
 167                  * debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY
 168                  * mechanism ensures the registers are updated on the
 169                  * world switch.
 170                  */
 171                 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
 172                         /* Enable breakpoints/watchpoints */
 173                         vcpu_sys_reg(vcpu, MDSCR_EL1) |= DBG_MDSCR_MDE;
 174
 175                         vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
 176                         vcpu->arch.debug_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         trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
 197         trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_sys_reg(vcpu, MDSCR_EL1));
 198 }
 199
 200 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
 201 {
 202         trace_kvm_arm_clear_debug(vcpu->guest_debug);
 203
 204         if (vcpu->guest_debug) {
 205                 restore_guest_debug_regs(vcpu);
 206
 207                 /*
 208                  * If we were using HW debug we need to restore the
 209                  * debug_ptr to the guest debug state.
 210                  */
 211                 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
 212                         kvm_arm_reset_debug_ptr(vcpu);
 213
 214                         trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
 215                                                 &vcpu->arch.debug_ptr->dbg_bcr[0],
 216                                                 &vcpu->arch.debug_ptr->dbg_bvr[0]);
 217
 218                         trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
 219                                                 &vcpu->arch.debug_ptr->dbg_wcr[0],
 220                                                 &vcpu->arch.debug_ptr->dbg_wvr[0]);
 221                 }
 222         }
 223 }
 224
 225
 226 /*
 227  * After successfully emulating an instruction, we might want to
 228  * return to user space with a KVM_EXIT_DEBUG. We can only do this
 229  * once the emulation is complete, though, so for userspace emulations
 230  * we have to wait until we have re-entered KVM before calling this
 231  * helper.
 232  *
 233  * Return true (and set exit_reason) to return to userspace or false
 234  * if no further action is required.
 235  */
 236 bool kvm_arm_handle_step_debug(struct kvm_vcpu *vcpu, struct kvm_run *run)
 237 {
 238         if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
 239                 run->exit_reason = KVM_EXIT_DEBUG;
 240                 run->debug.arch.hsr = ESR_ELx_EC_SOFTSTP_LOW << ESR_ELx_EC_SHIFT;
 241                 return true;
 242         }
 243         return false;
 244 }