linux-kernel - [PATCH v2 5/5] KVM: x86: Do not clear RFLAGS.TF when a singlestep trap occurs.

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Message-Id: <20161129204041.8839-6-khuey@kylehuey.com>
Date:   Tue, 29 Nov 2016 12:40:41 -0800
From:   Kyle Huey <me@...ehuey.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Joerg Roedel <joro@...tes.org>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v2 5/5] KVM: x86: Do not clear RFLAGS.TF when a singlestep trap occurs.

The trap flag stays set until software clears it.

Signed-off-by: Kyle Huey <khuey@...ehuey.com>
---
 arch/x86/kvm/x86.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7b38c5e..dd6b41e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5414,17 +5414,16 @@ static void kvm_vcpu_check_singlestep(struct kvm_vcpu *vcpu, unsigned long rflag
 		if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP) {
 			kvm_run->debug.arch.dr6 = DR6_BS | DR6_FIXED_1 |
 						  DR6_RTM;
 			kvm_run->debug.arch.pc = vcpu->arch.singlestep_rip;
 			kvm_run->debug.arch.exception = DB_VECTOR;
 			kvm_run->exit_reason = KVM_EXIT_DEBUG;
 			*r = EMULATE_USER_EXIT;
 		} else {
-			vcpu->arch.emulate_ctxt.eflags &= ~X86_EFLAGS_TF;
 			/*
 			 * "Certain debug exceptions may clear bit 0-3.  The
 			 * remaining contents of the DR6 register are never
 			 * cleared by the processor".
 			 */
 			vcpu->arch.dr6 &= ~15;
 			vcpu->arch.dr6 |= DR6_BS | DR6_RTM;
 			kvm_queue_exception(vcpu, DB_VECTOR);
-- 
2.10.2