linux-kernel - Re: [PATCH v2] KVM:x86: Clean up ModR/M "reg" initialization in reg op decoding

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Date:   Fri, 9 Sep 2022 21:47:53 +0800
From:   Liam Ni <zhiguangni01@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org, x86@...nel.org,
        pbonzini@...hat.com, tglx@...utronix.de,
        dave.hansen@...ux.intel.com
Subject: Re: [PATCH v2] KVM:x86: Clean up ModR/M "reg" initialization in reg
 op decoding

On Thu, 8 Sept 2022 at 23:50, Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Thu, Sep 08, 2022, Liam Ni wrote:
> > From: Liam Ni <zhiguangni01@...il.com>
> >
> > Refactor decode_register_operand() to get the ModR/M register if and
> > only if the instruction uses a ModR/M encoding to make it more obvious
> > how the register operand is retrieved.
> >
> > Signed-off-by: Liam Ni <zhiguangni01@...il.com>
> > ---
>
> Pushed to branch `for_paolo/6.1` at:
>
>     https://github.com/sean-jc/linux.git
>
> with the below nit sqaushed.  Unless you hear otherwise, it will make its way to
> kvm/queue "soon".
>
> Note, the commit IDs are not guaranteed to be stable.
>
> >  arch/x86/kvm/emulate.c | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> > index f092c54d1a2f..879b52af763a 100644
> > --- a/arch/x86/kvm/emulate.c
> > +++ b/arch/x86/kvm/emulate.c
> > @@ -1137,9 +1137,11 @@ static int em_fnstsw(struct x86_emulate_ctxt *ctxt)
> >  static void decode_register_operand(struct x86_emulate_ctxt *ctxt,
> >                                   struct operand *op)
> >  {
> > -     unsigned reg = ctxt->modrm_reg;
> > +     unsigned int reg;
> >
> > -     if (!(ctxt->d & ModRM))
> > +     if ((ctxt->d & ModRM))
>
> Only need one set of parentheses.

Sorry，  Should I prepare a new patch?

>
> > +             reg = ctxt->modrm_reg;
> > +     else
> >               reg = (ctxt->b & 7) | ((ctxt->rex_prefix & 1) << 3);
> >
> >       if (ctxt->d & Sse) {
> > --
> > 2.34.1
> >