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 u64 val = vcpu_read_sys_reg(vcpu, MDSCR_EL1); 50 51 vcpu->arch.guest_debug_preserved.mdscr_el1 = val; 52 53 trace_kvm_arm_set_dreg32("Saved MDSCR_EL1", 54 vcpu->arch.guest_debug_preserved.mdscr_el1); 55 } 56 57 static void restore_guest_debug_regs(struct kvm_vcpu *vcpu) 58 { 59 u64 val = vcpu->arch.guest_debug_preserved.mdscr_el1; 60 61 vcpu_write_sys_reg(vcpu, val, MDSCR_EL1); 62 63 trace_kvm_arm_set_dreg32("Restored MDSCR_EL1", 64 vcpu_read_sys_reg(vcpu, MDSCR_EL1)); 65 } 66 67 /** 68 * kvm_arm_init_debug - grab what we need for debug 69 * 70 * Currently the sole task of this function is to retrieve the initial 71 * value of mdcr_el2 so we can preserve MDCR_EL2.HPMN which has 72 * presumably been set-up by some knowledgeable bootcode. 73 * 74 * It is called once per-cpu during CPU hyp initialisation. 75 */ 76 77 void kvm_arm_init_debug(void) 78 { 79 __this_cpu_write(mdcr_el2, kvm_call_hyp(__kvm_get_mdcr_el2)); 80 } 81 82 /** 83 * kvm_arm_reset_debug_ptr - reset the debug ptr to point to the vcpu state 84 */ 85 86 void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu) 87 { 88 vcpu->arch.debug_ptr = &vcpu->arch.vcpu_debug_state; 89 } 90 91 /** 92 * kvm_arm_setup_debug - set up debug related stuff 93 * 94 * @vcpu: the vcpu pointer 95 * 96 * This is called before each entry into the hypervisor to setup any 97 * debug related registers. Currently this just ensures we will trap 98 * access to: 99 * - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR) 100 * - Debug ROM Address (MDCR_EL2_TDRA) 101 * - OS related registers (MDCR_EL2_TDOSA) 102 * - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB) 103 * 104 * Additionally, KVM only traps guest accesses to the debug registers if 105 * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY 106 * flag on vcpu->arch.flags). Since the guest must not interfere 107 * with the hardware state when debugging the guest, we must ensure that 108 * trapping is enabled whenever we are debugging the guest using the 109 * debug registers. 110 */ 111 112 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) 113 { 114 bool trap_debug = !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY); 115 unsigned long mdscr; 116 117 trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug); 118 119 /* 120 * This also clears MDCR_EL2_E2PB_MASK to disable guest access 121 * to the profiling buffer. 122 */ 123 vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK; 124 vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM | 125 MDCR_EL2_TPMS | 126 MDCR_EL2_TPMCR | 127 MDCR_EL2_TDRA | 128 MDCR_EL2_TDOSA); 129 130 /* Is Guest debugging in effect? */ 131 if (vcpu->guest_debug) { 132 /* Route all software debug exceptions to EL2 */ 133 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE; 134 135 /* Save guest debug state */ 136 save_guest_debug_regs(vcpu); 137 138 /* 139 * Single Step (ARM ARM D2.12.3 The software step state 140 * machine) 141 * 142 * If we are doing Single Step we need to manipulate 143 * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the 144 * step has occurred the hypervisor will trap the 145 * debug exception and we return to userspace. 146 * 147 * If the guest attempts to single step its userspace 148 * we would have to deal with a trapped exception 149 * while in the guest kernel. Because this would be 150 * hard to unwind we suppress the guest's ability to 151 * do so by masking MDSCR_EL.SS. 152 * 153 * This confuses guest debuggers which use 154 * single-step behind the scenes but everything 155 * returns to normal once the host is no longer 156 * debugging the system. 157 */ 158 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) { 159 *vcpu_cpsr(vcpu) |= DBG_SPSR_SS; 160 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1); 161 mdscr |= DBG_MDSCR_SS; 162 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1); 163 } else { 164 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1); 165 mdscr &= ~DBG_MDSCR_SS; 166 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1); 167 } 168 169 trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu)); 170 171 /* 172 * HW Breakpoints and watchpoints 173 * 174 * We simply switch the debug_ptr to point to our new 175 * external_debug_state which has been populated by the 176 * debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY 177 * mechanism ensures the registers are updated on the 178 * world switch. 179 */ 180 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) { 181 /* Enable breakpoints/watchpoints */ 182 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1); 183 mdscr |= DBG_MDSCR_MDE; 184 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1); 185 186 vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state; 187 vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY; 188 trap_debug = true; 189 190 trace_kvm_arm_set_regset("BKPTS", get_num_brps(), 191 &vcpu->arch.debug_ptr->dbg_bcr[0], 192 &vcpu->arch.debug_ptr->dbg_bvr[0]); 193 194 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(), 195 &vcpu->arch.debug_ptr->dbg_wcr[0], 196 &vcpu->arch.debug_ptr->dbg_wvr[0]); 197 } 198 } 199 200 BUG_ON(!vcpu->guest_debug && 201 vcpu->arch.debug_ptr != &vcpu->arch.vcpu_debug_state); 202 203 /* Trap debug register access */ 204 if (trap_debug) 205 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA; 206 207 /* If KDE or MDE are set, perform a full save/restore cycle. */ 208 if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE)) 209 vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY; 210 211 trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2); 212 trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1)); 213 } 214 215 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu) 216 { 217 trace_kvm_arm_clear_debug(vcpu->guest_debug); 218 219 if (vcpu->guest_debug) { 220 restore_guest_debug_regs(vcpu); 221 222 /* 223 * If we were using HW debug we need to restore the 224 * debug_ptr to the guest debug state. 225 */ 226 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) { 227 kvm_arm_reset_debug_ptr(vcpu); 228 229 trace_kvm_arm_set_regset("BKPTS", get_num_brps(), 230 &vcpu->arch.debug_ptr->dbg_bcr[0], 231 &vcpu->arch.debug_ptr->dbg_bvr[0]); 232 233 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(), 234 &vcpu->arch.debug_ptr->dbg_wcr[0], 235 &vcpu->arch.debug_ptr->dbg_wvr[0]); 236 } 237 } 238 } 239 240 241 /* 242 * After successfully emulating an instruction, we might want to 243 * return to user space with a KVM_EXIT_DEBUG. We can only do this 244 * once the emulation is complete, though, so for userspace emulations 245 * we have to wait until we have re-entered KVM before calling this 246 * helper. 247 * 248 * Return true (and set exit_reason) to return to userspace or false 249 * if no further action is required. 250 */ 251 bool kvm_arm_handle_step_debug(struct kvm_vcpu *vcpu, struct kvm_run *run) 252 { 253 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) { 254 run->exit_reason = KVM_EXIT_DEBUG; 255 run->debug.arch.hsr = ESR_ELx_EC_SOFTSTP_LOW << ESR_ELx_EC_SHIFT; 256 return true; 257 } 258 return false; 259 } 260