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 *
36 * When single-step is enabled by userspace, we tweak PSTATE.SS on every
37 * guest entry. Preserve PSTATE.SS so we can restore the original value
38 * for the vcpu after the single-step is disabled.
39 */
40 static void save_guest_debug_regs(struct kvm_vcpu *vcpu)
41 {
42 u64 val = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
43
44 vcpu->arch.guest_debug_preserved.mdscr_el1 = val;
45
46 trace_kvm_arm_set_dreg32("Saved MDSCR_EL1",
47 vcpu->arch.guest_debug_preserved.mdscr_el1);
48
49 vcpu->arch.guest_debug_preserved.pstate_ss =
50 (*vcpu_cpsr(vcpu) & DBG_SPSR_SS);
51 }
52
53 static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
54 {
55 u64 val = vcpu->arch.guest_debug_preserved.mdscr_el1;
56
57 vcpu_write_sys_reg(vcpu, val, MDSCR_EL1);
58
59 trace_kvm_arm_set_dreg32("Restored MDSCR_EL1",
60 vcpu_read_sys_reg(vcpu, MDSCR_EL1));
61
62 if (vcpu->arch.guest_debug_preserved.pstate_ss)
63 *vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
64 else
65 *vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;
66 }
67
68 /**
69 * kvm_arm_init_debug - grab what we need for debug
70 *
71 * Currently the sole task of this function is to retrieve the initial
72 * value of mdcr_el2 so we can preserve MDCR_EL2.HPMN which has
73 * presumably been set-up by some knowledgeable bootcode.
74 *
75 * It is called once per-cpu during CPU hyp initialisation.
76 */
77
78 void kvm_arm_init_debug(void)
79 {
80 __this_cpu_write(mdcr_el2, kvm_call_hyp_ret(__kvm_get_mdcr_el2));
81 }
82
83 /**
84 * kvm_arm_setup_mdcr_el2 - configure vcpu mdcr_el2 value
85 *
86 * @vcpu: the vcpu pointer
87 *
88 * This ensures we will trap access to:
89 * - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR)
90 * - Debug ROM Address (MDCR_EL2_TDRA)
91 * - OS related registers (MDCR_EL2_TDOSA)
92 * - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB)
93 * - Self-hosted Trace Filter controls (MDCR_EL2_TTRF)
94 * - Self-hosted Trace (MDCR_EL2_TTRF/MDCR_EL2_E2TB)
95 */
96 static void kvm_arm_setup_mdcr_el2(struct kvm_vcpu *vcpu)
97 {
98 /*
99 * This also clears MDCR_EL2_E2PB_MASK and MDCR_EL2_E2TB_MASK
100 * to disable guest access to the profiling and trace buffers
101 */
102 vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
103 vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
104 MDCR_EL2_TPMS |
105 MDCR_EL2_TTRF |
106 MDCR_EL2_TPMCR |
107 MDCR_EL2_TDRA |
108 MDCR_EL2_TDOSA);
109
110 /* Is the VM being debugged by userspace? */
111 if (vcpu->guest_debug)
112 /* Route all software debug exceptions to EL2 */
113 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
114
115 /*
116 * Trap debug register access when one of the following is true:
117 * - Userspace is using the hardware to debug the guest
118 * (KVM_GUESTDBG_USE_HW is set).
119 * - The guest is not using debug (DEBUG_DIRTY clear).
120 * - The guest has enabled the OS Lock (debug exceptions are blocked).
121 */
122 if ((vcpu->guest_debug & KVM_GUESTDBG_USE_HW) ||
123 !vcpu_get_flag(vcpu, DEBUG_DIRTY) ||
124 kvm_vcpu_os_lock_enabled(vcpu))
125 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
126
127 trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
128 }
129
130 /**
131 * kvm_arm_vcpu_init_debug - setup vcpu debug traps
132 *
133 * @vcpu: the vcpu pointer
134 *
135 * Set vcpu initial mdcr_el2 value.
136 */
137 void kvm_arm_vcpu_init_debug(struct kvm_vcpu *vcpu)
138 {
139 preempt_disable();
140 kvm_arm_setup_mdcr_el2(vcpu);
141 preempt_enable();
142 }
143
144 /**
145 * kvm_arm_reset_debug_ptr - reset the debug ptr to point to the vcpu state
146 * @vcpu: the vcpu pointer
147 */
148
149 void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
150 {
151 vcpu->arch.debug_ptr = &vcpu->arch.vcpu_debug_state;
152 }
153
154 /**
155 * kvm_arm_setup_debug - set up debug related stuff
156 *
157 * @vcpu: the vcpu pointer
158 *
159 * This is called before each entry into the hypervisor to setup any
160 * debug related registers.
161 *
162 * Additionally, KVM only traps guest accesses to the debug registers if
163 * the guest is not actively using them (see the DEBUG_DIRTY
164 * flag on vcpu->arch.iflags). Since the guest must not interfere
165 * with the hardware state when debugging the guest, we must ensure that
166 * trapping is enabled whenever we are debugging the guest using the
167 * debug registers.
168 */
169
170 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
171 {
172 unsigned long mdscr, orig_mdcr_el2 = vcpu->arch.mdcr_el2;
173
174 trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
175
176 kvm_arm_setup_mdcr_el2(vcpu);
177
178 /* Check if we need to use the debug registers. */
179 if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {
180 /* Save guest debug state */
181 save_guest_debug_regs(vcpu);
182
183 /*
184 * Single Step (ARM ARM D2.12.3 The software step state
185 * machine)
186 *
187 * If we are doing Single Step we need to manipulate
188 * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the
189 * step has occurred the hypervisor will trap the
190 * debug exception and we return to userspace.
191 *
192 * If the guest attempts to single step its userspace
193 * we would have to deal with a trapped exception
194 * while in the guest kernel. Because this would be
195 * hard to unwind we suppress the guest's ability to
196 * do so by masking MDSCR_EL.SS.
197 *
198 * This confuses guest debuggers which use
199 * single-step behind the scenes but everything
200 * returns to normal once the host is no longer
201 * debugging the system.
202 */
203 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
204 /*
205 * If the software step state at the last guest exit
206 * was Active-pending, we don't set DBG_SPSR_SS so
207 * that the state is maintained (to not run another
208 * single-step until the pending Software Step
209 * exception is taken).
210 */
211 if (!vcpu_get_flag(vcpu, DBG_SS_ACTIVE_PENDING))
212 *vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
213 else
214 *vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;
215
216 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
217 mdscr |= DBG_MDSCR_SS;
218 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
219 } else {
220 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
221 mdscr &= ~DBG_MDSCR_SS;
222 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
223 }
224
225 trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu));
226
227 /*
228 * HW Breakpoints and watchpoints
229 *
230 * We simply switch the debug_ptr to point to our new
231 * external_debug_state which has been populated by the
232 * debug ioctl. The existing DEBUG_DIRTY mechanism ensures
233 * the registers are updated on the world switch.
234 */
235 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
236 /* Enable breakpoints/watchpoints */
237 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
238 mdscr |= DBG_MDSCR_MDE;
239 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
240
241 vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
242 vcpu_set_flag(vcpu, DEBUG_DIRTY);
243
244 trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
245 &vcpu->arch.debug_ptr->dbg_bcr[0],
246 &vcpu->arch.debug_ptr->dbg_bvr[0]);
247
248 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
249 &vcpu->arch.debug_ptr->dbg_wcr[0],
250 &vcpu->arch.debug_ptr->dbg_wvr[0]);
251
252 /*
253 * The OS Lock blocks debug exceptions in all ELs when it is
254 * enabled. If the guest has enabled the OS Lock, constrain its
255 * effects to the guest. Emulate the behavior by clearing
256 * MDSCR_EL1.MDE. In so doing, we ensure that host debug
257 * exceptions are unaffected by guest configuration of the OS
258 * Lock.
259 */
260 } else if (kvm_vcpu_os_lock_enabled(vcpu)) {
261 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
262 mdscr &= ~DBG_MDSCR_MDE;
263 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
264 }
265 }
266
267 BUG_ON(!vcpu->guest_debug &&
268 vcpu->arch.debug_ptr != &vcpu->arch.vcpu_debug_state);
269
270 /* If KDE or MDE are set, perform a full save/restore cycle. */
271 if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
272 vcpu_set_flag(vcpu, DEBUG_DIRTY);
273
274 /* Write mdcr_el2 changes since vcpu_load on VHE systems */
275 if (has_vhe() && orig_mdcr_el2 != vcpu->arch.mdcr_el2)
276 write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
277
278 trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));
279 }
280
281 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
282 {
283 trace_kvm_arm_clear_debug(vcpu->guest_debug);
284
285 /*
286 * Restore the guest's debug registers if we were using them.
287 */
288 if (vcpu->guest_debug || kvm_vcpu_os_lock_enabled(vcpu)) {
289 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
290 if (!(*vcpu_cpsr(vcpu) & DBG_SPSR_SS))
291 /*
292 * Mark the vcpu as ACTIVE_PENDING
293 * until Software Step exception is taken.
294 */
295 vcpu_set_flag(vcpu, DBG_SS_ACTIVE_PENDING);
296 }
297
298 restore_guest_debug_regs(vcpu);
299
300 /*
301 * If we were using HW debug we need to restore the
302 * debug_ptr to the guest debug state.
303 */
304 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
305 kvm_arm_reset_debug_ptr(vcpu);
306
307 trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
308 &vcpu->arch.debug_ptr->dbg_bcr[0],
309 &vcpu->arch.debug_ptr->dbg_bvr[0]);
310
311 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
312 &vcpu->arch.debug_ptr->dbg_wcr[0],
313 &vcpu->arch.debug_ptr->dbg_wvr[0]);
314 }
315 }
316 }
317
318 void kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu *vcpu)
319 {
320 u64 dfr0;
321
322 /* For VHE, there is nothing to do */
323 if (has_vhe())
324 return;
325
326 dfr0 = read_sysreg(id_aa64dfr0_el1);
327 /*
328 * If SPE is present on this CPU and is available at current EL,
329 * we may need to check if the host state needs to be saved.
330 */
331 if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_PMSVer_SHIFT) &&
332 !(read_sysreg_s(SYS_PMBIDR_EL1) & BIT(PMBIDR_EL1_P_SHIFT)))
333 vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_SPE);
334
335 /* Check if we have TRBE implemented and available at the host */
336 if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_TraceBuffer_SHIFT) &&
337 !(read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_EL1_P))
338 vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_TRBE);
339 }
340
341 void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu)
342 {
343 vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_SPE);
344 vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_TRBE);
345 }
346
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.