linux-kernel - Re: [PATCH] KVM: x86: fix cocci warnings

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Date:   Tue, 16 Nov 2021 10:50:32 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Vihas Mak <makvihas@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     seanjc@...gle.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org,
        hpa@...or.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: fix cocci warnings

On 11/15/21 10:59, Vitaly Kuznetsov wrote:
> One minor remark: 'kvm_set_pte_rmapp()' handler is passed to
> 'kvm_handle_gfn_range()' which does
> 
>          bool ret = false;
> 
>          for_each_slot_rmap_range(...)
>                  ret |= handler(...);
> 
> and I find '|=' to not be very natural with booleans. I'm not sure it's
> worth changing though.

Changing that would be "harder" than it seems because "ret = ret || 
handler(...)" is wrong, and "|" is even more unnatural than "|=" (so 
much that clang warns about it).

In fact I wonder if "|=" with a bool might end up warning with clang, 
which we should check before applying this patch.  It doesn't seem to be 
in the original commit[1], but better safe than sorry: Nick, does clang 
intend to warn also about "ret |= fn()" and "ret &= fn()"?  Technically, 
it is a bitwise operation with side-effects in the RHS.

Paolo

[1] https://github.com/llvm/llvm-project/commit/f59cc9542bfb461