Re: [PATCH] KVM: x86/mmu: Fix a benign Bitwise vs. Logical OR mixup

[Jim Mattson]

On Wed, Jan 8, 2020 at 2:13 AM Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> wrote:
>
> Sean Christopherson <sean.j.christopherson@xxxxxxxxx> writes:
>
> > Use a Logical OR in __is_rsvd_bits_set() to combine the two reserved bit
> > checks, which are obviously intended to be logical statements.  Switching
> > to a Logical OR is functionally a nop, but allows the compiler to better
> > optimize the checks.
> >
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> > ---
> >  arch/x86/kvm/mmu/mmu.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 7269130ea5e2..72e845709027 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -3970,7 +3970,7 @@ __is_rsvd_bits_set(struct rsvd_bits_validate *rsvd_check, u64 pte, int level)
> >  {
> >       int bit7 = (pte >> 7) & 1, low6 = pte & 0x3f;
> >
> > -     return (pte & rsvd_check->rsvd_bits_mask[bit7][level-1]) |
> > +     return (pte & rsvd_check->rsvd_bits_mask[bit7][level-1]) ||
> >               ((rsvd_check->bad_mt_xwr & (1ull << low6)) != 0);
>
> Redundant parentheses detected!

I think you mean superfluous rather than redundant.

> >  }
>
> Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>

Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>