Linux kernel mirror (for testing)
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linux
1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Debug and Guest Debug support
4 *
5 * Copyright (C) 2015 - Linaro Ltd
6 * Author: Alex Bennée <alex.bennee@linaro.org>
7 */
8
9#include <linux/kvm_host.h>
10#include <linux/hw_breakpoint.h>
11
12#include <asm/debug-monitors.h>
13#include <asm/kvm_asm.h>
14#include <asm/kvm_arm.h>
15#include <asm/kvm_emulate.h>
16
17#include "trace.h"
18
19/* These are the bits of MDSCR_EL1 we may manipulate */
20#define MDSCR_EL1_DEBUG_MASK (DBG_MDSCR_SS | \
21 DBG_MDSCR_KDE | \
22 DBG_MDSCR_MDE)
23
24static DEFINE_PER_CPU(u32, mdcr_el2);
25
26/**
27 * save/restore_guest_debug_regs
28 *
29 * For some debug operations we need to tweak some guest registers. As
30 * a result we need to save the state of those registers before we
31 * make those modifications.
32 *
33 * Guest access to MDSCR_EL1 is trapped by the hypervisor and handled
34 * after we have restored the preserved value to the main context.
35 */
36static void save_guest_debug_regs(struct kvm_vcpu *vcpu)
37{
38 u64 val = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
39
40 vcpu->arch.guest_debug_preserved.mdscr_el1 = val;
41
42 trace_kvm_arm_set_dreg32("Saved MDSCR_EL1",
43 vcpu->arch.guest_debug_preserved.mdscr_el1);
44}
45
46static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
47{
48 u64 val = vcpu->arch.guest_debug_preserved.mdscr_el1;
49
50 vcpu_write_sys_reg(vcpu, val, MDSCR_EL1);
51
52 trace_kvm_arm_set_dreg32("Restored MDSCR_EL1",
53 vcpu_read_sys_reg(vcpu, MDSCR_EL1));
54}
55
56/**
57 * kvm_arm_init_debug - grab what we need for debug
58 *
59 * Currently the sole task of this function is to retrieve the initial
60 * value of mdcr_el2 so we can preserve MDCR_EL2.HPMN which has
61 * presumably been set-up by some knowledgeable bootcode.
62 *
63 * It is called once per-cpu during CPU hyp initialisation.
64 */
65
66void kvm_arm_init_debug(void)
67{
68 __this_cpu_write(mdcr_el2, kvm_call_hyp_ret(__kvm_get_mdcr_el2));
69}
70
71/**
72 * kvm_arm_reset_debug_ptr - reset the debug ptr to point to the vcpu state
73 */
74
75void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
76{
77 vcpu->arch.debug_ptr = &vcpu->arch.vcpu_debug_state;
78}
79
80/**
81 * kvm_arm_setup_debug - set up debug related stuff
82 *
83 * @vcpu: the vcpu pointer
84 *
85 * This is called before each entry into the hypervisor to setup any
86 * debug related registers. Currently this just ensures we will trap
87 * access to:
88 * - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR)
89 * - Debug ROM Address (MDCR_EL2_TDRA)
90 * - OS related registers (MDCR_EL2_TDOSA)
91 * - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB)
92 * - Self-hosted Trace Filter controls (MDCR_EL2_TTRF)
93 *
94 * Additionally, KVM only traps guest accesses to the debug registers if
95 * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
96 * flag on vcpu->arch.flags). Since the guest must not interfere
97 * with the hardware state when debugging the guest, we must ensure that
98 * trapping is enabled whenever we are debugging the guest using the
99 * debug registers.
100 */
101
102void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
103{
104 bool trap_debug = !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY);
105 unsigned long mdscr, orig_mdcr_el2 = vcpu->arch.mdcr_el2;
106
107 trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
108
109 /*
110 * This also clears MDCR_EL2_E2PB_MASK to disable guest access
111 * to the profiling buffer.
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_TPMS |
116 MDCR_EL2_TTRF |
117 MDCR_EL2_TPMCR |
118 MDCR_EL2_TDRA |
119 MDCR_EL2_TDOSA);
120
121 /* Is Guest debugging in effect? */
122 if (vcpu->guest_debug) {
123 /* Route all software debug exceptions to EL2 */
124 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
125
126 /* Save guest debug state */
127 save_guest_debug_regs(vcpu);
128
129 /*
130 * Single Step (ARM ARM D2.12.3 The software step state
131 * machine)
132 *
133 * If we are doing Single Step we need to manipulate
134 * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the
135 * step has occurred the hypervisor will trap the
136 * debug exception and we return to userspace.
137 *
138 * If the guest attempts to single step its userspace
139 * we would have to deal with a trapped exception
140 * while in the guest kernel. Because this would be
141 * hard to unwind we suppress the guest's ability to
142 * do so by masking MDSCR_EL.SS.
143 *
144 * This confuses guest debuggers which use
145 * single-step behind the scenes but everything
146 * returns to normal once the host is no longer
147 * debugging the system.
148 */
149 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
150 *vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
151 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
152 mdscr |= DBG_MDSCR_SS;
153 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
154 } else {
155 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
156 mdscr &= ~DBG_MDSCR_SS;
157 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
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 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
174 mdscr |= DBG_MDSCR_MDE;
175 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
176
177 vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
178 vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
179 trap_debug = true;
180
181 trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
182 &vcpu->arch.debug_ptr->dbg_bcr[0],
183 &vcpu->arch.debug_ptr->dbg_bvr[0]);
184
185 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
186 &vcpu->arch.debug_ptr->dbg_wcr[0],
187 &vcpu->arch.debug_ptr->dbg_wvr[0]);
188 }
189 }
190
191 BUG_ON(!vcpu->guest_debug &&
192 vcpu->arch.debug_ptr != &vcpu->arch.vcpu_debug_state);
193
194 /* Trap debug register access */
195 if (trap_debug)
196 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
197
198 /* If KDE or MDE are set, perform a full save/restore cycle. */
199 if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
200 vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
201
202 /* Write mdcr_el2 changes since vcpu_load on VHE systems */
203 if (has_vhe() && orig_mdcr_el2 != vcpu->arch.mdcr_el2)
204 write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
205
206 trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
207 trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));
208}
209
210void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
211{
212 trace_kvm_arm_clear_debug(vcpu->guest_debug);
213
214 if (vcpu->guest_debug) {
215 restore_guest_debug_regs(vcpu);
216
217 /*
218 * If we were using HW debug we need to restore the
219 * debug_ptr to the guest debug state.
220 */
221 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
222 kvm_arm_reset_debug_ptr(vcpu);
223
224 trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
225 &vcpu->arch.debug_ptr->dbg_bcr[0],
226 &vcpu->arch.debug_ptr->dbg_bvr[0]);
227
228 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
229 &vcpu->arch.debug_ptr->dbg_wcr[0],
230 &vcpu->arch.debug_ptr->dbg_wvr[0]);
231 }
232 }
233}