linux-kernel - Re: [PATCH] KVM: x86: avoid warning with -Wbitwise-instead-of-logical

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Date:   Fri, 15 Oct 2021 10:46:25 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, seanjc@...gle.com, torvic9@...lbox.org,
        Jim Mattson <jmattson@...gle.com>, llvm@...ts.linux.dev
Subject: Re: [PATCH] KVM: x86: avoid warning with -Wbitwise-instead-of-logical

On Fri, Oct 15, 2021 at 9:37 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> On Fri, Oct 15, 2021 at 04:51:48AM -0400, Paolo Bonzini wrote:
> > This is a new warning in clang top-of-tree (will be clang 14):
> >
> > In file included from arch/x86/kvm/mmu/mmu.c:27:
> > arch/x86/kvm/mmu/spte.h:318:9: error: use of bitwise '|' with boolean operands [-Werror,-Wbitwise-instead-of-logical]
> >         return __is_bad_mt_xwr(rsvd_check, spte) |
> >                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> >                                                  ||
> > arch/x86/kvm/mmu/spte.h:318:9: note: cast one or both operands to int to silence this warning
> >
> > Reported-by: torvic9@...lbox.org
> > Suggested-by: Jim Mattson <jmattson@...gle.com>
> > Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
>
> Reviewed-by: Nathan Chancellor <nathan@...nel.org>

Link: https://github.com/ClangBuiltLinux/linux/issues/1474
Acked-by: Nick Desaulniers <ndesaulniers@...gle.com>

>
> > ---
> >  arch/x86/kvm/mmu/spte.h | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
> > index eb7b227fc6cf..32bc7268c9ea 100644
> > --- a/arch/x86/kvm/mmu/spte.h
> > +++ b/arch/x86/kvm/mmu/spte.h
> > @@ -314,9 +314,12 @@ static __always_inline bool is_rsvd_spte(struct rsvd_bits_validate *rsvd_check,
> >        * Use a bitwise-OR instead of a logical-OR to aggregate the reserved
> >        * bits and EPT's invalid memtype/XWR checks to avoid an extra Jcc
> >        * (this is extremely unlikely to be short-circuited as true).
> > +      *
> > +      * (int) avoids clang's "use of bitwise '|' with boolean operands"
> > +      * warning.
> >        */
> > -     return __is_bad_mt_xwr(rsvd_check, spte) |
> > -            __is_rsvd_bits_set(rsvd_check, spte, level);
> > +     return (int)__is_bad_mt_xwr(rsvd_check, spte) |
> > +            (int)__is_rsvd_bits_set(rsvd_check, spte, level);
> >  }
> >
> >  static inline bool spte_can_locklessly_be_made_writable(u64 spte)
> > --
> > 2.27.0
> >
> >
>


-- 
Thanks,
~Nick Desaulniers