2 * Debug and Guest Debug support
4 * Copyright (C) 2015 - Linaro Ltd
5 * Author: Alex Bennée <alex.bennee@linaro.org>
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.
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.
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/>.
20 #include <linux/kvm_host.h>
22 #include <asm/debug-monitors.h>
23 #include <asm/kvm_asm.h>
24 #include <asm/kvm_arm.h>
25 #include <asm/kvm_emulate.h>
27 /* These are the bits of MDSCR_EL1 we may manipulate */
28 #define MDSCR_EL1_DEBUG_MASK (DBG_MDSCR_SS | \
32 static DEFINE_PER_CPU(u32, mdcr_el2);
35 * save/restore_guest_debug_regs
37 * For some debug operations we need to tweak some guest registers. As
38 * a result we need to save the state of those registers before we
39 * make those modifications.
41 * Guest access to MDSCR_EL1 is trapped by the hypervisor and handled
42 * after we have restored the preserved value to the main context.
44 static void save_guest_debug_regs(struct kvm_vcpu *vcpu)
46 vcpu->arch.guest_debug_preserved.mdscr_el1 = vcpu_sys_reg(vcpu, MDSCR_EL1);
49 static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
51 vcpu_sys_reg(vcpu, MDSCR_EL1) = vcpu->arch.guest_debug_preserved.mdscr_el1;
55 * kvm_arm_init_debug - grab what we need for debug
57 * Currently the sole task of this function is to retrieve the initial
58 * value of mdcr_el2 so we can preserve MDCR_EL2.HPMN which has
59 * presumably been set-up by some knowledgeable bootcode.
61 * It is called once per-cpu during CPU hyp initialisation.
64 void kvm_arm_init_debug(void)
66 __this_cpu_write(mdcr_el2, kvm_call_hyp(__kvm_get_mdcr_el2));
70 * kvm_arm_reset_debug_ptr - reset the debug ptr to point to the vcpu state
73 void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
75 vcpu->arch.debug_ptr = &vcpu->arch.vcpu_debug_state;
79 * kvm_arm_setup_debug - set up debug related stuff
81 * @vcpu: the vcpu pointer
83 * This is called before each entry into the hypervisor to setup any
84 * debug related registers. Currently this just ensures we will trap
86 * - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR)
87 * - Debug ROM Address (MDCR_EL2_TDRA)
88 * - OS related registers (MDCR_EL2_TDOSA)
90 * Additionally, KVM only traps guest accesses to the debug registers if
91 * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
92 * flag on vcpu->arch.debug_flags). Since the guest must not interfere
93 * with the hardware state when debugging the guest, we must ensure that
94 * trapping is enabled whenever we are debugging the guest using the
98 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
100 bool trap_debug = !(vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY);
102 vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
103 vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
108 /* Is Guest debugging in effect? */
109 if (vcpu->guest_debug) {
110 /* Route all software debug exceptions to EL2 */
111 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
113 /* Save guest debug state */
114 save_guest_debug_regs(vcpu);
117 * Single Step (ARM ARM D2.12.3 The software step state
120 * If we are doing Single Step we need to manipulate
121 * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the
122 * step has occurred the hypervisor will trap the
123 * debug exception and we return to userspace.
125 * If the guest attempts to single step its userspace
126 * we would have to deal with a trapped exception
127 * while in the guest kernel. Because this would be
128 * hard to unwind we suppress the guest's ability to
129 * do so by masking MDSCR_EL.SS.
131 * This confuses guest debuggers which use
132 * single-step behind the scenes but everything
133 * returns to normal once the host is no longer
134 * debugging the system.
136 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
137 *vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
138 vcpu_sys_reg(vcpu, MDSCR_EL1) |= DBG_MDSCR_SS;
140 vcpu_sys_reg(vcpu, MDSCR_EL1) &= ~DBG_MDSCR_SS;
144 * HW Breakpoints and watchpoints
146 * We simply switch the debug_ptr to point to our new
147 * external_debug_state which has been populated by the
148 * debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY
149 * mechanism ensures the registers are updated on the
152 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
153 /* Enable breakpoints/watchpoints */
154 vcpu_sys_reg(vcpu, MDSCR_EL1) |= DBG_MDSCR_MDE;
156 vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
157 vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_DIRTY;
162 BUG_ON(!vcpu->guest_debug &&
163 vcpu->arch.debug_ptr != &vcpu->arch.vcpu_debug_state);
165 /* Trap debug register access */
167 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
170 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
172 if (vcpu->guest_debug) {
173 restore_guest_debug_regs(vcpu);
176 * If we were using HW debug we need to restore the
177 * debug_ptr to the guest debug state.
179 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW)
180 kvm_arm_reset_debug_ptr(vcpu);