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
24 static 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 */
save_guest_debug_regs(struct kvm_vcpu * vcpu)36 static 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
restore_guest_debug_regs(struct kvm_vcpu * vcpu)46 static 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
kvm_arm_init_debug(void)66 void 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_setup_mdcr_el2 - configure vcpu mdcr_el2 value
73 *
74 * @vcpu: the vcpu pointer
75 *
76 * This ensures we will trap access to:
77 * - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR)
78 * - Debug ROM Address (MDCR_EL2_TDRA)
79 * - OS related registers (MDCR_EL2_TDOSA)
80 * - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB)
81 * - Self-hosted Trace Filter controls (MDCR_EL2_TTRF)
82 */
kvm_arm_setup_mdcr_el2(struct kvm_vcpu * vcpu)83 static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu)
84 {
85 /*
86 * This also clears MDCR_EL2_E2PB_MASK to disable guest access
87 * to the profiling buffer.
88 */
89 vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
90 vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
91 MDCR_EL2_TPMS |
92 MDCR_EL2_TTRF |
93 MDCR_EL2_TPMCR |
94 MDCR_EL2_TDRA |
95 MDCR_EL2_TDOSA);
96
97 /* Is the VM being debugged by userspace? */
98 if (vcpu->guest_debug)
99 /* Route all software debug exceptions to EL2 */
100 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
101
102 /*
103 * Trap debug register access when one of the following is true:
104 * - Userspace is using the hardware to debug the guest
105 * (KVM_GUESTDBG_USE_HW is set).
106 * - The guest is not using debug (KVM_ARM64_DEBUG_DIRTY is clear).
107 */
108 if ((vcpu->guest_debug & KVM_GUESTDBG_USE_HW) ||
109 !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY))
110 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
111
112 trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
113 }
114
115 /**
116 * kvm_arm_vcpu_init_debug - setup vcpu debug traps
117 *
118 * @vcpu: the vcpu pointer
119 *
120 * Set vcpu initial mdcr_el2 value.
121 */
kvm_arm_vcpu_init_debug(struct kvm_vcpu * vcpu)122 void kvm_arm_vcpu_init_debug(struct kvm_vcpu *vcpu)
123 {
124 preempt_disable();
125 kvm_arm_setup_mdcr_el2(vcpu);
126 preempt_enable();
127 }
128
129 /**
130 * kvm_arm_reset_debug_ptr - reset the debug ptr to point to the vcpu state
131 */
132
kvm_arm_reset_debug_ptr(struct kvm_vcpu * vcpu)133 void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
134 {
135 vcpu->arch.debug_ptr = &vcpu->arch.vcpu_debug_state;
136 }
137
138 /**
139 * kvm_arm_setup_debug - set up debug related stuff
140 *
141 * @vcpu: the vcpu pointer
142 *
143 * This is called before each entry into the hypervisor to setup any
144 * debug related registers.
145 *
146 * Additionally, KVM only traps guest accesses to the debug registers if
147 * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
148 * flag on vcpu->arch.flags). Since the guest must not interfere
149 * with the hardware state when debugging the guest, we must ensure that
150 * trapping is enabled whenever we are debugging the guest using the
151 * debug registers.
152 */
153
kvm_arm_setup_debug(struct kvm_vcpu * vcpu)154 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
155 {
156 unsigned long mdscr, orig_mdcr_el2 = vcpu->arch.mdcr_el2;
157
158 trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
159
160 kvm_arm_setup_mdcr_el2(vcpu);
161
162 /* Is Guest debugging in effect? */
163 if (vcpu->guest_debug) {
164 /* Save guest debug state */
165 save_guest_debug_regs(vcpu);
166
167 /*
168 * Single Step (ARM ARM D2.12.3 The software step state
169 * machine)
170 *
171 * If we are doing Single Step we need to manipulate
172 * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the
173 * step has occurred the hypervisor will trap the
174 * debug exception and we return to userspace.
175 *
176 * If the guest attempts to single step its userspace
177 * we would have to deal with a trapped exception
178 * while in the guest kernel. Because this would be
179 * hard to unwind we suppress the guest's ability to
180 * do so by masking MDSCR_EL.SS.
181 *
182 * This confuses guest debuggers which use
183 * single-step behind the scenes but everything
184 * returns to normal once the host is no longer
185 * debugging the system.
186 */
187 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
188 *vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
189 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
190 mdscr |= DBG_MDSCR_SS;
191 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
192 } else {
193 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
194 mdscr &= ~DBG_MDSCR_SS;
195 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
196 }
197
198 trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu));
199
200 /*
201 * HW Breakpoints and watchpoints
202 *
203 * We simply switch the debug_ptr to point to our new
204 * external_debug_state which has been populated by the
205 * debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY
206 * mechanism ensures the registers are updated on the
207 * world switch.
208 */
209 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
210 /* Enable breakpoints/watchpoints */
211 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
212 mdscr |= DBG_MDSCR_MDE;
213 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
214
215 vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
216 vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
217
218 trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
219 &vcpu->arch.debug_ptr->dbg_bcr[0],
220 &vcpu->arch.debug_ptr->dbg_bvr[0]);
221
222 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
223 &vcpu->arch.debug_ptr->dbg_wcr[0],
224 &vcpu->arch.debug_ptr->dbg_wvr[0]);
225 }
226 }
227
228 BUG_ON(!vcpu->guest_debug &&
229 vcpu->arch.debug_ptr != &vcpu->arch.vcpu_debug_state);
230
231 /* If KDE or MDE are set, perform a full save/restore cycle. */
232 if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
233 vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
234
235 /* Write mdcr_el2 changes since vcpu_load on VHE systems */
236 if (has_vhe() && orig_mdcr_el2 != vcpu->arch.mdcr_el2)
237 write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
238
239 trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));
240 }
241
kvm_arm_clear_debug(struct kvm_vcpu * vcpu)242 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
243 {
244 trace_kvm_arm_clear_debug(vcpu->guest_debug);
245
246 if (vcpu->guest_debug) {
247 restore_guest_debug_regs(vcpu);
248
249 /*
250 * If we were using HW debug we need to restore the
251 * debug_ptr to the guest debug state.
252 */
253 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
254 kvm_arm_reset_debug_ptr(vcpu);
255
256 trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
257 &vcpu->arch.debug_ptr->dbg_bcr[0],
258 &vcpu->arch.debug_ptr->dbg_bvr[0]);
259
260 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
261 &vcpu->arch.debug_ptr->dbg_wcr[0],
262 &vcpu->arch.debug_ptr->dbg_wvr[0]);
263 }
264 }
265 }
266