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(u64, 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 * - Self-hosted Trace (MDCR_EL2_TTRF/MDCR_EL2_E2TB)
83 */
kvm_arm_setup_mdcr_el2(struct kvm_vcpu * vcpu)84 static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu)
85 {
86 /*
87 * This also clears MDCR_EL2_E2PB_MASK and MDCR_EL2_E2TB_MASK
88 * to disable guest access to the profiling and trace buffers
89 */
90 vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
91 vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
92 MDCR_EL2_TPMS |
93 MDCR_EL2_TTRF |
94 MDCR_EL2_TPMCR |
95 MDCR_EL2_TDRA |
96 MDCR_EL2_TDOSA);
97
98 /* Is the VM being debugged by userspace? */
99 if (vcpu->guest_debug)
100 /* Route all software debug exceptions to EL2 */
101 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
102
103 /*
104 * Trap debug register access when one of the following is true:
105 * - Userspace is using the hardware to debug the guest
106 * (KVM_GUESTDBG_USE_HW is set).
107 * - The guest is not using debug (KVM_ARM64_DEBUG_DIRTY is clear).
108 * - The guest has enabled the OS Lock (debug exceptions are blocked).
109 */
110 if ((vcpu->guest_debug & KVM_GUESTDBG_USE_HW) ||
111 !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY) ||
112 kvm_vcpu_os_lock_enabled(vcpu))
113 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
114
115 trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
116 }
117
118 /**
119 * kvm_arm_vcpu_init_debug - setup vcpu debug traps
120 *
121 * @vcpu: the vcpu pointer
122 *
123 * Set vcpu initial mdcr_el2 value.
124 */
kvm_arm_vcpu_init_debug(struct kvm_vcpu * vcpu)125 void kvm_arm_vcpu_init_debug(struct kvm_vcpu *vcpu)
126 {
127 preempt_disable();
128 kvm_arm_setup_mdcr_el2(vcpu);
129 preempt_enable();
130 }
131
132 /**
133 * kvm_arm_reset_debug_ptr - reset the debug ptr to point to the vcpu state
134 */
135
kvm_arm_reset_debug_ptr(struct kvm_vcpu * vcpu)136 void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
137 {
138 vcpu->arch.debug_ptr = &vcpu->arch.vcpu_debug_state;
139 }
140
141 /**
142 * kvm_arm_setup_debug - set up debug related stuff
143 *
144 * @vcpu: the vcpu pointer
145 *
146 * This is called before each entry into the hypervisor to setup any
147 * debug related registers.
148 *
149 * Additionally, KVM only traps guest accesses to the debug registers if
150 * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
151 * flag on vcpu->arch.flags). Since the guest must not interfere
152 * with the hardware state when debugging the guest, we must ensure that
153 * trapping is enabled whenever we are debugging the guest using the
154 * debug registers.
155 */
156
kvm_arm_setup_debug(struct kvm_vcpu * vcpu)157 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
158 {
159 unsigned long mdscr, orig_mdcr_el2 = vcpu->arch.mdcr_el2;
160
161 trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
162
163 kvm_arm_setup_mdcr_el2(vcpu);
164
165 /* Check if we need to use the debug registers. */
166 if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {
167 /* Save guest debug state */
168 save_guest_debug_regs(vcpu);
169
170 /*
171 * Single Step (ARM ARM D2.12.3 The software step state
172 * machine)
173 *
174 * If we are doing Single Step we need to manipulate
175 * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the
176 * step has occurred the hypervisor will trap the
177 * debug exception and we return to userspace.
178 *
179 * If the guest attempts to single step its userspace
180 * we would have to deal with a trapped exception
181 * while in the guest kernel. Because this would be
182 * hard to unwind we suppress the guest's ability to
183 * do so by masking MDSCR_EL.SS.
184 *
185 * This confuses guest debuggers which use
186 * single-step behind the scenes but everything
187 * returns to normal once the host is no longer
188 * debugging the system.
189 */
190 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
191 *vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
192 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
193 mdscr |= DBG_MDSCR_SS;
194 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
195 } else {
196 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
197 mdscr &= ~DBG_MDSCR_SS;
198 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
199 }
200
201 trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu));
202
203 /*
204 * HW Breakpoints and watchpoints
205 *
206 * We simply switch the debug_ptr to point to our new
207 * external_debug_state which has been populated by the
208 * debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY
209 * mechanism ensures the registers are updated on the
210 * world switch.
211 */
212 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
213 /* Enable breakpoints/watchpoints */
214 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
215 mdscr |= DBG_MDSCR_MDE;
216 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
217
218 vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
219 vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
220
221 trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
222 &vcpu->arch.debug_ptr->dbg_bcr[0],
223 &vcpu->arch.debug_ptr->dbg_bvr[0]);
224
225 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
226 &vcpu->arch.debug_ptr->dbg_wcr[0],
227 &vcpu->arch.debug_ptr->dbg_wvr[0]);
228
229 /*
230 * The OS Lock blocks debug exceptions in all ELs when it is
231 * enabled. If the guest has enabled the OS Lock, constrain its
232 * effects to the guest. Emulate the behavior by clearing
233 * MDSCR_EL1.MDE. In so doing, we ensure that host debug
234 * exceptions are unaffected by guest configuration of the OS
235 * Lock.
236 */
237 } else if (kvm_vcpu_os_lock_enabled(vcpu)) {
238 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
239 mdscr &= ~DBG_MDSCR_MDE;
240 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
241 }
242 }
243
244 BUG_ON(!vcpu->guest_debug &&
245 vcpu->arch.debug_ptr != &vcpu->arch.vcpu_debug_state);
246
247 /* If KDE or MDE are set, perform a full save/restore cycle. */
248 if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
249 vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
250
251 /* Write mdcr_el2 changes since vcpu_load on VHE systems */
252 if (has_vhe() && orig_mdcr_el2 != vcpu->arch.mdcr_el2)
253 write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
254
255 trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));
256 }
257
kvm_arm_clear_debug(struct kvm_vcpu * vcpu)258 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
259 {
260 trace_kvm_arm_clear_debug(vcpu->guest_debug);
261
262 /*
263 * Restore the guest's debug registers if we were using them.
264 */
265 if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {
266 restore_guest_debug_regs(vcpu);
267
268 /*
269 * If we were using HW debug we need to restore the
270 * debug_ptr to the guest debug state.
271 */
272 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
273 kvm_arm_reset_debug_ptr(vcpu);
274
275 trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
276 &vcpu->arch.debug_ptr->dbg_bcr[0],
277 &vcpu->arch.debug_ptr->dbg_bvr[0]);
278
279 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
280 &vcpu->arch.debug_ptr->dbg_wcr[0],
281 &vcpu->arch.debug_ptr->dbg_wvr[0]);
282 }
283 }
284 }
285
kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu * vcpu)286 void kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu *vcpu)
287 {
288 u64 dfr0;
289
290 /* For VHE, there is nothing to do */
291 if (has_vhe())
292 return;
293
294 dfr0 = read_sysreg(id_aa64dfr0_el1);
295 /*
296 * If SPE is present on this CPU and is available at current EL,
297 * we may need to check if the host state needs to be saved.
298 */
299 if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_PMSVER_SHIFT) &&
300 !(read_sysreg_s(SYS_PMBIDR_EL1) & BIT(SYS_PMBIDR_EL1_P_SHIFT)))
301 vcpu->arch.flags |= KVM_ARM64_DEBUG_STATE_SAVE_SPE;
302
303 /* Check if we have TRBE implemented and available at the host */
304 if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_TRBE_SHIFT) &&
305 !(read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_PROG))
306 vcpu->arch.flags |= KVM_ARM64_DEBUG_STATE_SAVE_TRBE;
307 }
308
kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu * vcpu)309 void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu)
310 {
311 vcpu->arch.flags &= ~(KVM_ARM64_DEBUG_STATE_SAVE_SPE |
312 KVM_ARM64_DEBUG_STATE_SAVE_TRBE);
313 }
314