linux-kernel - [PATCH v4 4/6] KVM: x86: Bump hypercall stat prior to fully completing hypercall

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Message-ID: <20241128004344.4072099-5-seanjc@google.com>
Date: Wed, 27 Nov 2024 16:43:42 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Tom Lendacky <thomas.lendacky@....com>, Binbin Wu <binbin.wu@...ux.intel.com>, 
	Isaku Yamahata <isaku.yamahata@...el.com>, Kai Huang <kai.huang@...el.com>, 
	Xiaoyao Li <xiaoyao.li@...el.com>
Subject: [PATCH v4 4/6] KVM: x86: Bump hypercall stat prior to fully
 completing hypercall

Increment the "hypercalls" stat for KVM hypercalls as soon as KVM knows
it will skip the guest instruction, i.e. once KVM is committed to emulating
the hypercall.  Waiting until completion adds no known value, and creates a
discrepancy where the stat will be bumped if KVM exits to userspace as a
result of trying to skip the instruction, but not if the hypercall itself
exits.

Handling the stat in common code will also avoid the need for another
helper to dedup code when TDX comes along (TDX needs a separate completion
path due to GPR usage differences).

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/x86.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 13fe5d6eb8f3..11434752b467 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9979,7 +9979,6 @@ static int complete_hypercall_exit(struct kvm_vcpu *vcpu)
 	if (!is_64_bit_hypercall(vcpu))
 		ret = (u32)ret;
 	kvm_rax_write(vcpu, ret);
-	++vcpu->stat.hypercalls;
 	return kvm_skip_emulated_instruction(vcpu);
 }
 
@@ -9990,6 +9989,8 @@ unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr,
 {
 	unsigned long ret;
 
+	++vcpu->stat.hypercalls;
+
 	trace_kvm_hypercall(nr, a0, a1, a2, a3);
 
 	if (!op_64_bit) {
@@ -10070,7 +10071,6 @@ unsigned long __kvm_emulate_hypercall(struct kvm_vcpu *vcpu, unsigned long nr,
 	}
 
 out:
-	++vcpu->stat.hypercalls;
 	return ret;
 }
 EXPORT_SYMBOL_GPL(__kvm_emulate_hypercall);
-- 
2.47.0.338.g60cca15819-goog