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 * 99 * Additionally, KVM only traps guest accesses to the debug registers if 100 * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY 101 * flag on vcpu->arch.debug_flags). Since the guest must not interfere 102 * with the hardware state when debugging the guest, we must ensure that 103 * trapping is enabled whenever we are debugging the guest using the 104 * debug registers. 105 */ 106 107 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) 108 { 109 bool trap_debug = !(vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY); 110 111 trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug); 112 113 vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK; 114 vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM | 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 vcpu_sys_reg(vcpu, MDSCR_EL1) |= DBG_MDSCR_SS; 150 } else { 151 vcpu_sys_reg(vcpu, MDSCR_EL1) &= ~DBG_MDSCR_SS; 152 } 153 154 trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu)); 155 156 /* 157 * HW Breakpoints and watchpoints 158 * 159 * We simply switch the debug_ptr to point to our new 160 * external_debug_state which has been populated by the 161 * debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY 162 * mechanism ensures the registers are updated on the 163 * world switch. 164 */ 165 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) { 166 /* Enable breakpoints/watchpoints */ 167 vcpu_sys_reg(vcpu, MDSCR_EL1) |= DBG_MDSCR_MDE; 168 169 vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state; 170 vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_DIRTY; 171 trap_debug = true; 172 173 trace_kvm_arm_set_regset("BKPTS", get_num_brps(), 174 &vcpu->arch.debug_ptr->dbg_bcr[0], 175 &vcpu->arch.debug_ptr->dbg_bvr[0]); 176 177 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(), 178 &vcpu->arch.debug_ptr->dbg_wcr[0], 179 &vcpu->arch.debug_ptr->dbg_wvr[0]); 180 } 181 } 182 183 BUG_ON(!vcpu->guest_debug && 184 vcpu->arch.debug_ptr != &vcpu->arch.vcpu_debug_state); 185 186 /* Trap debug register access */ 187 if (trap_debug) 188 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA; 189 190 trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2); 191 trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_sys_reg(vcpu, MDSCR_EL1)); 192 } 193 194 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu) 195 { 196 trace_kvm_arm_clear_debug(vcpu->guest_debug); 197 198 if (vcpu->guest_debug) { 199 restore_guest_debug_regs(vcpu); 200 201 /* 202 * If we were using HW debug we need to restore the 203 * debug_ptr to the guest debug state. 204 */ 205 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) { 206 kvm_arm_reset_debug_ptr(vcpu); 207 208 trace_kvm_arm_set_regset("BKPTS", get_num_brps(), 209 &vcpu->arch.debug_ptr->dbg_bcr[0], 210 &vcpu->arch.debug_ptr->dbg_bvr[0]); 211 212 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(), 213 &vcpu->arch.debug_ptr->dbg_wcr[0], 214 &vcpu->arch.debug_ptr->dbg_wvr[0]); 215 } 216 } 217 } 218