linux-kernel - [PATCH 2/2] KVM: VMX: Allow toggling bits in MSR_IA32_RTIT

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Message-ID: <20241101185031.1799556-3-seanjc@google.com>
Date: Fri,  1 Nov 2024 11:50:31 -0700
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, 
	Adrian Hunter <adrian.hunter@...el.com>
Subject: [PATCH 2/2] KVM: VMX: Allow toggling bits in MSR_IA32_RTIT_CTL when
 enable bit is cleared

From: Adrian Hunter <adrian.hunter@...el.com>

Allow toggling other bits in MSR_IA32_RTIT_CTL if the enable bit is being
cleared, the existing logic simply ignores the enable bit.  E.g. KVM will
incorrectly reject a write of '0' to stop tracing.

Fixes: bf8c55d8dc09 ("KVM: x86: Implement Intel PT MSRs read/write emulation")
Signed-off-by: Adrian Hunter <adrian.hunter@...el.com>
[sean: rework changelog, drop stable@]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/vmx.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 087504fb1589..9b9d115c4824 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -1636,7 +1636,8 @@ static int vmx_rtit_ctl_check(struct kvm_vcpu *vcpu, u64 data)
 	 * result in a #GP unless the same write also clears TraceEn.
 	 */
 	if ((vmx->pt_desc.guest.ctl & RTIT_CTL_TRACEEN) &&
-		((vmx->pt_desc.guest.ctl ^ data) & ~RTIT_CTL_TRACEEN))
+	    (data & RTIT_CTL_TRACEEN) &&
+	    data != vmx->pt_desc.guest.ctl)
 		return 1;
 
 	/*
-- 
2.47.0.163.g1226f6d8fa-goog