linux-kernel - Re: [PATCH v5 2/5] KVM: x86: Drop kvm_x86_ops.set_dr6() in favor of a new KVM

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Message-ID: <aC9h_9CyZ4DMAAi_@google.com>
Date: Thu, 22 May 2025 10:42:23 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Maxim Levitsky <mlevitsk@...hat.com>
Cc: kvm@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>, 
	Thomas Gleixner <tglx@...utronix.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org, 
	x86@...nel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v5 2/5] KVM: x86: Drop kvm_x86_ops.set_dr6() in favor of a
 new KVM_RUN flag

On Wed, May 21, 2025, Maxim Levitsky wrote:
> From: Sean Christopherson <seanjc@...gle.com>
> 
> Instruct vendor code to load the guest's DR6 into hardware via a new
> KVM_RUN flag, and remove kvm_x86_ops.set_dr6(), whose sole purpose was to
> load vcpu->arch.dr6 into hardware when DR6 can be read/written directly
> by the guest.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/include/asm/kvm-x86-ops.h |  1 -
>  arch/x86/include/asm/kvm_host.h    |  2 +-
>  arch/x86/kvm/svm/svm.c             | 10 ++++++----
>  arch/x86/kvm/vmx/main.c            |  9 ---------
>  arch/x86/kvm/vmx/vmx.c             |  9 +++------
>  arch/x86/kvm/x86.c                 |  2 +-
>  6 files changed, 11 insertions(+), 22 deletions(-)

As alluded to in the previous patch, TDX should WARN, because guest DR6 is owned
by the TDX module (the KVM_DEBUGREG_AUTO_SWITCH guard prevents KVM_RUN_LOAD_GUEST_DR6
from being set).