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 */
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
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
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_reset_debug_ptr - reset the debug ptr to point to the vcpu state
73 */
74
75 void 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 *
93 * Additionally, KVM only traps guest accesses to the debug registers if
94 * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
95 * flag on vcpu->arch.flags). Since the guest must not interfere
96 * with the hardware state when debugging the guest, we must ensure that
97 * trapping is enabled whenever we are debugging the guest using the
98 * debug registers.
99 */
100
101 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
102 {
103 bool trap_debug = !(vcpu->arch.flags & KVM_ARM64_DEBUG_DIRTY);
104 unsigned long mdscr, orig_mdcr_el2 = vcpu->arch.mdcr_el2;
105
106 trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
107
108 /*
109 * This also clears MDCR_EL2_E2PB_MASK to disable guest access
110 * to the profiling buffer.
111 */
112 vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
113 vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
114 MDCR_EL2_TPMS |
115 MDCR_EL2_TPMCR |
116 MDCR_EL2_TDRA |
117 MDCR_EL2_TDOSA);
118
119 /* Is Guest debugging in effect? */
120 if (vcpu->guest_debug) {
121 /* Route all software debug exceptions to EL2 */
122 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
123
124 /* Save guest debug state */
125 save_guest_debug_regs(vcpu);
126
127 /*
128 * Single Step (ARM ARM D2.12.3 The software step state
129 * machine)
130 *
131 * If we are doing Single Step we need to manipulate
132 * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the
133 * step has occurred the hypervisor will trap the
134 * debug exception and we return to userspace.
135 *
136 * If the guest attempts to single step its userspace
137 * we would have to deal with a trapped exception
138 * while in the guest kernel. Because this would be
139 * hard to unwind we suppress the guest's ability to
140 * do so by masking MDSCR_EL.SS.
141 *
142 * This confuses guest debuggers which use
143 * single-step behind the scenes but everything
144 * returns to normal once the host is no longer
145 * debugging the system.
146 */
147 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
148 *vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
149 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
150 mdscr |= DBG_MDSCR_SS;
151 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
152 } else {
153 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
154 mdscr &= ~DBG_MDSCR_SS;
155 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
156 }
157
158 trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu));
159
160 /*
161 * HW Breakpoints and watchpoints
162 *
163 * We simply switch the debug_ptr to point to our new
164 * external_debug_state which has been populated by the
165 * debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY
166 * mechanism ensures the registers are updated on the
167 * world switch.
168 */
169 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
170 /* Enable breakpoints/watchpoints */
171 mdscr = vcpu_read_sys_reg(vcpu, MDSCR_EL1);
172 mdscr |= DBG_MDSCR_MDE;
173 vcpu_write_sys_reg(vcpu, mdscr, MDSCR_EL1);
174
175 vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
176 vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
177 trap_debug = true;
178
179 trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
180 &vcpu->arch.debug_ptr->dbg_bcr[0],
181 &vcpu->arch.debug_ptr->dbg_bvr[0]);
182
183 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
184 &vcpu->arch.debug_ptr->dbg_wcr[0],
185 &vcpu->arch.debug_ptr->dbg_wvr[0]);
186 }
187 }
188
189 BUG_ON(!vcpu->guest_debug &&
190 vcpu->arch.debug_ptr != &vcpu->arch.vcpu_debug_state);
191
192 /* Trap debug register access */
193 if (trap_debug)
194 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA;
195
196 /* If KDE or MDE are set, perform a full save/restore cycle. */
197 if (vcpu_read_sys_reg(vcpu, MDSCR_EL1) & (DBG_MDSCR_KDE | DBG_MDSCR_MDE))
198 vcpu->arch.flags |= KVM_ARM64_DEBUG_DIRTY;
199
200 /* Write mdcr_el2 changes since vcpu_load on VHE systems */
201 if (has_vhe() && orig_mdcr_el2 != vcpu->arch.mdcr_el2)
202 write_sysreg(vcpu->arch.mdcr_el2, mdcr_el2);
203
204 trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
205 trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_read_sys_reg(vcpu, MDSCR_EL1));
206 }
207
208 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
209 {
210 trace_kvm_arm_clear_debug(vcpu->guest_debug);
211
212 if (vcpu->guest_debug) {
213 restore_guest_debug_regs(vcpu);
214
215 /*
216 * If we were using HW debug we need to restore the
217 * debug_ptr to the guest debug state.
218 */
219 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
220 kvm_arm_reset_debug_ptr(vcpu);
221
222 trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
223 &vcpu->arch.debug_ptr->dbg_bcr[0],
224 &vcpu->arch.debug_ptr->dbg_bvr[0]);
225
226 trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
227 &vcpu->arch.debug_ptr->dbg_wcr[0],
228 &vcpu->arch.debug_ptr->dbg_wvr[0]);
229 }
230 }
231 }