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

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Message-ID: <2d44c75f-00df-3cae-31a8-982a0b95f0b0@redhat.com>
Date:   Wed, 6 May 2020 18:09:23 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Peter Xu <peterx@...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 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.

Paolo

> Reviewed-by: Peter Xu <peterx@...hat.com>