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