blob: 52ccd696f9af8cb7f393fd245edb300069126356 [file] [log] [blame]
From 6b8714ea471e946910f1a7436a348a587d5b1718 Mon Sep 17 00:00:00 2001
From: Felipe Franciosi <>
Date: Tue, 19 May 2020 08:11:22 +0000
Subject: [PATCH] KVM: x86: respect singlestep when emulating instruction
commit 384dea1c9183880be183cfaae161d99aafd16df6 upstream.
When userspace configures KVM_GUESTDBG_SINGLESTEP, KVM will manage the
presence of X86_EFLAGS_TF via kvm_set/get_rflags on vcpus. The actual
rflag bit is therefore hidden from callers.
That includes init_emulate_ctxt() which uses the value returned from
kvm_get_flags() to set ctxt->tf. As a result, x86_emulate_instruction()
will skip a single step, leaving singlestep_rip stale and not returning
to userspace.
This resolves the issue by observing the vcpu guest_debug configuration
alongside ctxt->tf in x86_emulate_instruction(), performing the single
step if set.
Signed-off-by: Felipe Franciosi <>
Message-Id: <>
Signed-off-by: Paolo Bonzini <>
Signed-off-by: Paul Gortmaker <>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index db1809c4677f..c4ab1fb89480 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -6683,7 +6683,7 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
if (!ctxt->have_exception ||
exception_type(ctxt->exception.vector) == EXCPT_TRAP) {
kvm_rip_write(vcpu, ctxt->eip);
- if (r == EMULATE_DONE && ctxt->tf)
+ if (r == EMULATE_DONE && (ctxt->tf || (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)))
kvm_vcpu_do_singlestep(vcpu, &r);
__kvm_set_rflags(vcpu, ctxt->eflags);