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Linux/arch/arm64/kvm/debug.c

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  1 /*
  2  * Debug and Guest Debug support
  3  *
  4  * Copyright (C) 2015 - Linaro Ltd
  5  * Author: Alex Bennée <alex.bennee@linaro.org>
  6  *
  7  * This program is free software; you can redistribute it and/or modify
  8  * it under the terms of the GNU General Public License version 2 as
  9  * published by the Free Software Foundation.
 10  *
 11  * This program is distributed in the hope that it will be useful,
 12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
 13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 14  * GNU General Public License for more details.
 15  *
 16  * You should have received a copy of the GNU General Public License
 17  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 18  */
 19 
 20 #include <linux/kvm_host.h>
 21 #include <linux/hw_breakpoint.h>
 22 
 23 #include <asm/debug-monitors.h>
 24 #include <asm/kvm_asm.h>
 25 #include <asm/kvm_arm.h>
 26 #include <asm/kvm_emulate.h>
 27 
 28 #include "trace.h"
 29 
 30 /* These are the bits of MDSCR_EL1 we may manipulate */
 31 #define MDSCR_EL1_DEBUG_MASK    (DBG_MDSCR_SS | \
 32                                 DBG_MDSCR_KDE | \
 33                                 DBG_MDSCR_MDE)
 34 
 35 static DEFINE_PER_CPU(u32, mdcr_el2);
 36 
 37 /**
 38  * save/restore_guest_debug_regs
 39  *
 40  * For some debug operations we need to tweak some guest registers. As
 41  * a result we need to save the state of those registers before we
 42  * make those modifications.
 43  *
 44  * Guest access to MDSCR_EL1 is trapped by the hypervisor and handled
 45  * after we have restored the preserved value to the main context.
 46  */
 47 static void save_guest_debug_regs(struct kvm_vcpu *vcpu)
 48 {
 49         vcpu->arch.guest_debug_preserved.mdscr_el1 = vcpu_sys_reg(vcpu, MDSCR_EL1);
 50 
 51         trace_kvm_arm_set_dreg32("Saved MDSCR_EL1",
 52                                 vcpu->arch.guest_debug_preserved.mdscr_el1);
 53 }
 54 
 55 static void restore_guest_debug_regs(struct kvm_vcpu *vcpu)
 56 {
 57         vcpu_sys_reg(vcpu, MDSCR_EL1) = vcpu->arch.guest_debug_preserved.mdscr_el1;
 58 
 59         trace_kvm_arm_set_dreg32("Restored MDSCR_EL1",
 60                                 vcpu_sys_reg(vcpu, MDSCR_EL1));
 61 }
 62 
 63 /**
 64  * kvm_arm_init_debug - grab what we need for debug
 65  *
 66  * Currently the sole task of this function is to retrieve the initial
 67  * value of mdcr_el2 so we can preserve MDCR_EL2.HPMN which has
 68  * presumably been set-up by some knowledgeable bootcode.
 69  *
 70  * It is called once per-cpu during CPU hyp initialisation.
 71  */
 72 
 73 void kvm_arm_init_debug(void)
 74 {
 75         __this_cpu_write(mdcr_el2, kvm_call_hyp(__kvm_get_mdcr_el2));
 76 }
 77 
 78 /**
 79  * kvm_arm_reset_debug_ptr - reset the debug ptr to point to the vcpu state
 80  */
 81 
 82 void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu)
 83 {
 84         vcpu->arch.debug_ptr = &vcpu->arch.vcpu_debug_state;
 85 }
 86 
 87 /**
 88  * kvm_arm_setup_debug - set up debug related stuff
 89  *
 90  * @vcpu:       the vcpu pointer
 91  *
 92  * This is called before each entry into the hypervisor to setup any
 93  * debug related registers. Currently this just ensures we will trap
 94  * access to:
 95  *  - Performance monitors (MDCR_EL2_TPM/MDCR_EL2_TPMCR)
 96  *  - Debug ROM Address (MDCR_EL2_TDRA)
 97  *  - OS related registers (MDCR_EL2_TDOSA)
 98  *  - Statistical profiler (MDCR_EL2_TPMS/MDCR_EL2_E2PB)
 99  *
100  * Additionally, KVM only traps guest accesses to the debug registers if
101  * the guest is not actively using them (see the KVM_ARM64_DEBUG_DIRTY
102  * flag on vcpu->arch.debug_flags).  Since the guest must not interfere
103  * with the hardware state when debugging the guest, we must ensure that
104  * trapping is enabled whenever we are debugging the guest using the
105  * debug registers.
106  */
107 
108 void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
109 {
110         bool trap_debug = !(vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY);
111 
112         trace_kvm_arm_setup_debug(vcpu, vcpu->guest_debug);
113 
114         /*
115          * This also clears MDCR_EL2_E2PB_MASK to disable guest access
116          * to the profiling buffer.
117          */
118         vcpu->arch.mdcr_el2 = __this_cpu_read(mdcr_el2) & MDCR_EL2_HPMN_MASK;
119         vcpu->arch.mdcr_el2 |= (MDCR_EL2_TPM |
120                                 MDCR_EL2_TPMS |
121                                 MDCR_EL2_TPMCR |
122                                 MDCR_EL2_TDRA |
123                                 MDCR_EL2_TDOSA);
124 
125         /* Is Guest debugging in effect? */
126         if (vcpu->guest_debug) {
127                 /* Route all software debug exceptions to EL2 */
128                 vcpu->arch.mdcr_el2 |= MDCR_EL2_TDE;
129 
130                 /* Save guest debug state */
131                 save_guest_debug_regs(vcpu);
132 
133                 /*
134                  * Single Step (ARM ARM D2.12.3 The software step state
135                  * machine)
136                  *
137                  * If we are doing Single Step we need to manipulate
138                  * the guest's MDSCR_EL1.SS and PSTATE.SS. Once the
139                  * step has occurred the hypervisor will trap the
140                  * debug exception and we return to userspace.
141                  *
142                  * If the guest attempts to single step its userspace
143                  * we would have to deal with a trapped exception
144                  * while in the guest kernel. Because this would be
145                  * hard to unwind we suppress the guest's ability to
146                  * do so by masking MDSCR_EL.SS.
147                  *
148                  * This confuses guest debuggers which use
149                  * single-step behind the scenes but everything
150                  * returns to normal once the host is no longer
151                  * debugging the system.
152                  */
153                 if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
154                         *vcpu_cpsr(vcpu) |=  DBG_SPSR_SS;
155                         vcpu_sys_reg(vcpu, MDSCR_EL1) |= DBG_MDSCR_SS;
156                 } else {
157                         vcpu_sys_reg(vcpu, MDSCR_EL1) &= ~DBG_MDSCR_SS;
158                 }
159 
160                 trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu));
161 
162                 /*
163                  * HW Breakpoints and watchpoints
164                  *
165                  * We simply switch the debug_ptr to point to our new
166                  * external_debug_state which has been populated by the
167                  * debug ioctl. The existing KVM_ARM64_DEBUG_DIRTY
168                  * mechanism ensures the registers are updated on the
169                  * world switch.
170                  */
171                 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
172                         /* Enable breakpoints/watchpoints */
173                         vcpu_sys_reg(vcpu, MDSCR_EL1) |= DBG_MDSCR_MDE;
174 
175                         vcpu->arch.debug_ptr = &vcpu->arch.external_debug_state;
176                         vcpu->arch.debug_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         trace_kvm_arm_set_dreg32("MDCR_EL2", vcpu->arch.mdcr_el2);
197         trace_kvm_arm_set_dreg32("MDSCR_EL1", vcpu_sys_reg(vcpu, MDSCR_EL1));
198 }
199 
200 void kvm_arm_clear_debug(struct kvm_vcpu *vcpu)
201 {
202         trace_kvm_arm_clear_debug(vcpu->guest_debug);
203 
204         if (vcpu->guest_debug) {
205                 restore_guest_debug_regs(vcpu);
206 
207                 /*
208                  * If we were using HW debug we need to restore the
209                  * debug_ptr to the guest debug state.
210                  */
211                 if (vcpu->guest_debug & KVM_GUESTDBG_USE_HW) {
212                         kvm_arm_reset_debug_ptr(vcpu);
213 
214                         trace_kvm_arm_set_regset("BKPTS", get_num_brps(),
215                                                 &vcpu->arch.debug_ptr->dbg_bcr[0],
216                                                 &vcpu->arch.debug_ptr->dbg_bvr[0]);
217 
218                         trace_kvm_arm_set_regset("WAPTS", get_num_wrps(),
219                                                 &vcpu->arch.debug_ptr->dbg_wcr[0],
220                                                 &vcpu->arch.debug_ptr->dbg_wvr[0]);
221                 }
222         }
223 }
224 
225 
226 /*
227  * After successfully emulating an instruction, we might want to
228  * return to user space with a KVM_EXIT_DEBUG. We can only do this
229  * once the emulation is complete, though, so for userspace emulations
230  * we have to wait until we have re-entered KVM before calling this
231  * helper.
232  *
233  * Return true (and set exit_reason) to return to userspace or false
234  * if no further action is required.
235  */
236 bool kvm_arm_handle_step_debug(struct kvm_vcpu *vcpu, struct kvm_run *run)
237 {
238         if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
239                 run->exit_reason = KVM_EXIT_DEBUG;
240                 run->debug.arch.hsr = ESR_ELx_EC_SOFTSTP_LOW << ESR_ELx_EC_SHIFT;
241                 return true;
242         }
243         return false;
244 }
245 

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