linux-kernel - [PATCH v2 6/9] KVM: x86: Move kvm_set_rflags() up before kvm_vcpu_do

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Message-Id: <30964c504cb4683f53093f5f37c2081825db35dc.1766066076.git.houwenlong.hwl@antgroup.com>
Date: Thu, 18 Dec 2025 22:00:41 +0800
From: Hou Wenlong <houwenlong.hwl@...group.com>
To: kvm@...r.kernel.org
Cc: Lai Jiangshan <jiangshan.ljs@...group.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 6/9] KVM: x86: Move kvm_set_rflags() up before kvm_vcpu_do_singlestep()

The single-step trap #DB should be injected after the instruction
completes, as 'ctxt->tf' already records the old value of
'X86_EFLAGS_TF'.  Therefore, it's okay to move kvm_set_rflags() up
before kvm_vcpu_do_single_step() to align it more closely with hardware
behavior.

No functional change intended.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
---
 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 44c2886589d7..7352c2114bab 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9593,10 +9593,10 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 			if (ctxt->is_branch)
 				kvm_pmu_branch_retired(vcpu);
 			kvm_rip_write(vcpu, ctxt->eip);
+			__kvm_set_rflags(vcpu, ctxt->eflags);
 			if (r && (ctxt->tf || (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)))
 				r = kvm_vcpu_do_singlestep(vcpu);
 			kvm_x86_call(update_emulated_instruction)(vcpu);
-			__kvm_set_rflags(vcpu, ctxt->eflags);
 		}
 
 		/*
-- 
2.31.1