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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. Currently this just ensures we will trap
145  * access to:
146  *  - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR)
147  *  - Debug ROM Address (MDCR_EL2_TDRA)
148  *  - OS related registers (MDCR_EL2_TDOSA)
149  *  - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB)
150  *  - Self-hosted Trace (MDCR_EL2_TTRF/MDCR_EL2_E2TB)
151  *
152  * Additionally, KVM only traps guest accesses to the debug registers if
153  * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
154  * flag on vcpu->arch.flags).  Since the guest must not interfere
155  * with the hardware state when debugging the guest, we must ensure that
156  * trapping is enabled whenever we are debugging the guest using the
157  * debug registers.
158  */
159 
kvm_arm_setup_debug(struct kvm_vcpu * vcpu)160 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
161 {
162 	unsigned long mdscr, orig_mdcr_el2 = vcpu->arch.mdcr_el2;
163 
164 	trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
165 
166 	kvm_arm_setup_mdcr_el2(vcpu);
167 
168 	/* Is Guest debugging in effect? */
169 	if (vcpu->guest_debug) {
170 		/* Save guest debug state */
171 		save_guest_debug_regs(vcpu);
172 
173 		/*
174 		 * Single Step (ARM ARM D2.12.3 The software step state
175 		 * machine)
176 		 *
177 		 * If we are doing Single Step we need to manipulate
178 		 * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the
179 		 * step has occurred the hypervisor will trap the
180 		 * debug exception and we return to userspace.
181 		 *
182 		 * If the guest attempts to single step its userspace
183 		 * we would have to deal with a trapped exception
184 		 * while in the guest kernel. Because this would be
185 		 * hard to unwind we suppress the guest's ability to
186 		 * do so by masking MDSCR_EL.SS.
187 		 *
188 		 * This confuses guest debuggers which use
189 		 * single-step behind the scenes but everything
190 		 * returns to normal once the host is no longer
191 		 * debugging the system.
192 		 */
193 		if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
194 			*vcpu_cpsr(vcpu) |=  DBG_SPSR_SS;
195 			mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
196 			mdscr |= DBG_MDSCR_SS;
197 			vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
198 		} else {
199 			mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
200 			mdscr &= ~DBG_MDSCR_SS;
201 			vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
202 		}
203 
204 		trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu));
205 
206 		/*
207 		 * HW Breakpoints and watchpoints
208 		 *
209 		 * We simply switch the debug_ptr to point to our new
210 		 * external_debug_state which has been populated by the
211 		 * debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY
212 		 * mechanism ensures the registers are updated on the
213 		 * world switch.
214 		 */
215 		if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
216 			/* Enable breakpoints/watchpoints */
217 			mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
218 			mdscr |= DBG_MDSCR_MDE;
219 			vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
220 
221 			vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
222 			vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
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 
234 	BUG_ON(!vcpu->guest_debug &&
235 		vcpu->arch.debug_ptr != &vcpu->arch.vcpu_debug_state);
236 
237 	/* If KDE or MDE are set, perform a full save/restore cycle. */
238 	if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
239 		vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
240 
241 	/* Write mdcr_el2 changes since vcpu_load on VHE systems */
242 	if (has_vhe() && orig_mdcr_el2 != vcpu->arch.mdcr_el2)
243 		write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
244 
245 	trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));
246 }
247 
kvm_arm_clear_debug(struct kvm_vcpu * vcpu)248 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
249 {
250 	trace_kvm_arm_clear_debug(vcpu->guest_debug);
251 
252 	if (vcpu->guest_debug) {
253 		restore_guest_debug_regs(vcpu);
254 
255 		/*
256 		 * If we were using HW debug we need to restore the
257 		 * debug_ptr to the guest debug state.
258 		 */
259 		if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
260 			kvm_arm_reset_debug_ptr(vcpu);
261 
262 			trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
263 						&vcpu->arch.debug_ptr->dbg_bcr[0],
264 						&vcpu->arch.debug_ptr->dbg_bvr[0]);
265 
266 			trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
267 						&vcpu->arch.debug_ptr->dbg_wcr[0],
268 						&vcpu->arch.debug_ptr->dbg_wvr[0]);
269 		}
270 	}
271 }
272 
kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu * vcpu)273 void kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu *vcpu)
274 {
275 	u64 dfr0;
276 
277 	/* For VHE, there is nothing to do */
278 	if (has_vhe())
279 		return;
280 
281 	dfr0 = read_sysreg(id_aa64dfr0_el1);
282 	/*
283 	 * If SPE is present on this CPU and is available at current EL,
284 	 * we may need to check if the host state needs to be saved.
285 	 */
286 	if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_PMSVER_SHIFT) &&
287 	    !(read_sysreg_s(SYS_PMBIDR_EL1) & BIT(SYS_PMBIDR_EL1_P_SHIFT)))
288 		vcpu->arch.flags |= KVM_ARM64_DEBUG_STATE_SAVE_SPE;
289 
290 	/* Check if we have TRBE implemented and available at the host */
291 	if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_TRBE_SHIFT) &&
292 	    !(read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_PROG))
293 		vcpu->arch.flags |= KVM_ARM64_DEBUG_STATE_SAVE_TRBE;
294 }
295 
kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu * vcpu)296 void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu)
297 {
298 	vcpu->arch.flags &= ~(KVM_ARM64_DEBUG_STATE_SAVE_SPE |
299 			      KVM_ARM64_DEBUG_STATE_SAVE_TRBE);
300 }
301