linux-kernel - Re: [PATCH 7/9] KVM: x86: simplify dr6 accessors in kvm_x86

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Date:   Wed, 6 May 2020 13:52:06 -0400
From:   Peter Xu <peterx@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH 7/9] KVM: x86: simplify dr6 accessors in kvm_x86_ops

On Wed, May 06, 2020 at 06:09:23PM +0200, Paolo Bonzini wrote:
> On 06/05/20 18:06, Peter Xu wrote:
> > On Wed, May 06, 2020 at 07:10:32AM -0400, Paolo Bonzini wrote:
> >> kvm_x86_ops.set_dr6 is only ever called with vcpu->arch.dr6 as the
> >> second argument, and for both SVM and VMX the VMCB value is kept
> >> synchronized with vcpu->arch.dr6 on #DB; we can therefore remove the
> >> read accessor.
> >>
> >> For the write accessor we can avoid the retpoline penalty on Intel
> >> by accepting a NULL value and just skipping the call in that case.
> >>
> >> Suggested-by: Sean Christopherson <sean.j.christopherson@...el.com>
> >> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> > (I think this patch and the previous one seem to be the same as the previous
> >  version.  Anyway...)
> 
> Yes, I placed them here because they are needed to solve the SVM bugs in
> patch 8.  Sorry for not adding your Reviewed-by.

That's not a problem to me. :) Instead I'm more afraid of not noticing some
trivial difference in the patch comparing to the last one.

Thanks,

-- 
Peter Xu