[PATCH REPOST 3/3] arm64: kvm: Fix single step for guest skipped instructions
Julien Thierry
julien.thierry at arm.com
Tue Oct 3 10:05:52 PDT 2017
Software Step exception is missing after trapping instruction from the guest.
We need to set the PSR.SS to 0 for the guest vcpu before resuming guest
execution.
Signed-off-by: Julien Thierry <julien.thierry at arm.com>
Cc: Christoffer Dall <christoffer.dall at linaro.org>
Cc: Marc Zyngier <marc.zyngier at arm.com>
Cc: Alex Bennée <alex.bennee at linaro.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will.deacon at arm.com>
---
arch/arm64/include/asm/kvm_asm.h | 2 ++
arch/arm64/include/asm/kvm_emulate.h | 2 ++
arch/arm64/kvm/debug.c | 17 ++++++++++++++++-
arch/arm64/kvm/hyp/switch.c | 10 ++++++++++
4 files changed, 30 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 26a64d0..398bbaa 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -32,6 +32,8 @@
#define KVM_ARM64_DEBUG_DIRTY_SHIFT 0
#define KVM_ARM64_DEBUG_DIRTY (1 << KVM_ARM64_DEBUG_DIRTY_SHIFT)
+#define KVM_ARM64_DEBUG_INST_SKIP_SHIFT 1
+#define KVM_ARM64_DEBUG_INST_SKIP (1 << KVM_ARM64_DEBUG_INST_SKIP_SHIFT)
#define kvm_ksym_ref(sym) \
({ \
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index e5df3fc..ee02dd2ee 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -95,6 +95,8 @@ static inline void kvm_skip_instr(struct kvm_vcpu *vcpu, bool is_wide_instr)
kvm_skip_instr32(vcpu, is_wide_instr);
else
*vcpu_pc(vcpu) += 4;
+ /* Let debug engine know we skipped an instruction */
+ vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_INST_SKIP;
}
static inline void vcpu_set_thumb(struct kvm_vcpu *vcpu)
diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index dbadfaf..b5fcb96 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -151,12 +151,27 @@ void kvm_arm_setup_debug(struct kvm_vcpu *vcpu)
* debugging the system.
*/
if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
- *vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
+ /*
+ * Taking a Software step exception, context being
+ * stepped has PSTATE.SS == 0. In order to step the next
+ * instruction, we need to reset this bit.
+ * If we skipped an instruction while single stepping,
+ * we want to get a software step exception for the
+ * skipped instruction (i.e. as soon as we return to the
+ * guest). This is obtained by returning to the guest
+ * with PSTATE.SS cleared.
+ */
+ if (!(vcpu->arch.debug_flags & KVM_ARM64_DEBUG_INST_SKIP))
+ *vcpu_cpsr(vcpu) |= DBG_SPSR_SS;
+ else
+ *vcpu_cpsr(vcpu) &= ~DBG_SPSR_SS;
vcpu_sys_reg(vcpu, MDSCR_EL1) |= DBG_MDSCR_SS;
} else {
vcpu_sys_reg(vcpu, MDSCR_EL1) &= ~DBG_MDSCR_SS;
}
+ vcpu->arch.debug_flags &= ~KVM_ARM64_DEBUG_INST_SKIP;
+
trace_kvm_arm_set_dreg32("SPSR_EL2", *vcpu_cpsr(vcpu));
/*
diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index 945e79c..34fe215 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -22,6 +22,7 @@
#include <asm/kvm_emulate.h>
#include <asm/kvm_hyp.h>
#include <asm/fpsimd.h>
+#include <asm/debug-monitors.h>
static bool __hyp_text __fpsimd_enabled_nvhe(void)
{
@@ -276,6 +277,8 @@ static void __hyp_text __skip_instr(struct kvm_vcpu *vcpu)
}
write_sysreg_el2(*vcpu_pc(vcpu), elr);
+
+ write_sysreg_el2(read_sysreg_el2(spsr) & ~DBG_SPSR_SS, spsr);
}
int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
@@ -343,6 +346,13 @@ int __hyp_text __kvm_vcpu_run(struct kvm_vcpu *vcpu)
if (ret == -1) {
/* Promote an illegal access to an SError */
__skip_instr(vcpu);
+
+ /*
+ * We're not jumping back, let debug setup know
+ * we skipped an instruction.
+ */
+ vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_INST_SKIP;
+
exit_code = ARM_EXCEPTION_EL1_SERROR;
}
--
1.9.1
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