[PATCH v5 03/13] KVM: nSVM: Move VMRUN instruction retirement after entering guest mode

Yosry Ahmed
2026-04-30T20:28:01Z

A successful VMRUN retires in guest mode and should be counted by the
PMU as a guest instruction. However, __kvm_skip_emulated_instruction()
is called before entering guest mode to advance L1's RIP to the
instruction following VMRUN. This is needed as the RIP is saved in
vmcb01 to be restored on VM-Exit.

Since VMRUN emulation is the only caller of
__kvm_skip_emulated_instruction(), move retiring instructions for PMU
purposes to its wrapper, leaving __kvm_skip_emulated_instruction() as a
transparent wrapper around the vendor-specific calls.

Note that this is currently a noop because KVM does not virtualize
Host-Only/Guest-Only PMC controls yet, so all instructions are counted
regardless of the vCPU's host/guest state. But this change is needed for
the incoming support for Host-Only/Guest-Only controls to count VMRUN
correctly.

Signed-off-by: Yosry Ahmed <yosry@kernel.org>
---
arch/x86/kvm/svm/nested.c | 9 ++++++++-
arch/x86/kvm/x86.c | 11 +++--------
2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 0f6ea490d707b..58c78c889a812 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -30,6 +30,7 @@
#include "lapic.h"
#include "svm.h"
#include "hyperv.h"
+#include "pmu.h"

#define CC KVM_NESTED_VMENTER_CONSISTENCY_CHECK

@@ -1135,7 +1136,7 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
return 0;

if (ret)
- return 1;
+ goto insn_retired;

/*
* Since vmcb01 is not in use, we can use it to store some of the L1
@@ -1165,6 +1166,12 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
nested_svm_vmexit(svm);
}

+insn_retired:
+ /*
+ * A successful VMRUN is counted by the PMU in guest mode, so only
+ * retire the instruction after potentially entering guest mode.
+ */
+ kvm_pmu_instruction_retired(vcpu);
return 1;
}

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 31dc48a8111e5..08be0a63b93bd 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9274,14 +9274,7 @@ static int kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu)

int __kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu)
{
- int r;
-
- r = kvm_x86_call(skip_emulated_instruction)(vcpu);
- if (unlikely(!r))
- return 0;
-
- kvm_pmu_instruction_retired(vcpu);
- return r;
+ return kvm_x86_call(skip_emulated_instruction)(vcpu);
}
EXPORT_SYMBOL_FOR_KVM_INTERNAL(__kvm_skip_emulated_instruction);

@@ -9294,6 +9287,8 @@ int kvm_skip_emulated_instruction(struct kvm_vcpu *vcpu)
if (unlikely(!r))
return 0;

+ kvm_pmu_instruction_retired(vcpu);
+
/*
* rflags is the old, "raw" value of the flags. The new value has
* not been saved yet.
--
2.54.0.545.g6539524ca2-goog