linux-kernel - Re: [PATCH] x86/bugs/mmio: Rename mmio_stale_data_clear to cpu_buf_vm

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Message-ID: <20250411001702.p5g2gjtundwjtbwy@desk>
Date: Thu, 10 Apr 2025 17:17:02 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org,
	Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH] x86/bugs/mmio: Rename mmio_stale_data_clear to
 cpu_buf_vm_clear

On Thu, Apr 10, 2025 at 04:35:58PM -0700, Sean Christopherson wrote:
> > > I like the idea of tying the static key back to X86_FEATURE_CLEAR_CPU_BUF, but
> > > when looking at just the usage in KVM, "cpu_buf_vm_clear" doesn't provide any
> > > hints as to when/why KVM needs to clear buffers.
> > 
> > Thats fair, can we cover that with a comment like below:
> > 
> > ---
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index c79720aad3df..cddad4a6eb46 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -7358,6 +7358,10 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
> >  	 * mitigation for MDS is done late in VMentry and is still
> >  	 * executed in spite of L1D Flush. This is because an extra VERW
> >  	 * should not matter much after the big hammer L1D Flush.
> > +	 *
> > +	 * cpu_buf_vm_clear is used when system is not vulnerable to MDS/TAA,
> > +	 * but is affected by MMIO Stale Data that only needs mitigation
> > +	 * against a rogue guest.
> 
> Would this be accurate?

I believe this is accurate as things stand today. But, when Attack Vector
Control series leverages cpu_buf_vm_clear, the comment also needs to be
updated.