linux-kernel - Re: [PATCH] KVM: x86: Load DR6 with guest value only before entering .vcpu

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Message-ID: <173958027023.1189487.12347713108460200107.b4-ty@google.com>
Date: Fri, 14 Feb 2025 16:50:09 -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, 
	John Stultz <jstultz@...gle.com>, Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH] KVM: x86: Load DR6 with guest value only before entering
 .vcpu_run() loop

On Fri, 24 Jan 2025 17:18:33 -0800, Sean Christopherson wrote:
> Move the conditional loading of hardware DR6 with the guest's DR6 value
> out of the core .vcpu_run() loop to fix a bug where KVM can load hardware
> with a stale vcpu->arch.dr6.
> 
> When the guest accesses a DR and host userspace isn't debugging the guest,
> KVM disables DR interception and loads the guest's values into hardware on
> VM-Enter and saves them on VM-Exit.  This allows the guest to access DRs
> at will, e.g. so that a sequence of DR accesses to configure a breakpoint
> only generates one VM-Exit.
> 
> [...]

Applied to kvm-x86 fixes, thanks!

[1/1] KVM: x86: Load DR6 with guest value only before entering .vcpu_run() loop
      https://github.com/kvm-x86/linux/commit/c2fee09fc167

--
https://github.com/kvm-x86/linux/tree/next