linux-kernel - Re: [PATCH v2] kvm: x86: mmu: Add cast to negated bitmasks in update_permission

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Date:   Mon, 25 Jun 2018 19:01:42 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Matthias Kaehlcke <mka@...omium.org>, rkrcmar@...hat.com,
        Thomas Gleixner <tglx@...utronix.de>, hpa@...or.com,
        x86@...nel.org, kvm@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>, joe@...ches.com
Subject: Re: [PATCH v2] kvm: x86: mmu: Add cast to negated bitmasks in
 update_permission_bitmask()

On 25/06/2018 18:47, Nick Desaulniers wrote:
> Here's an actual bug this warning caught applied to drivers/input/:
> 
> dae1a432ab1f ("Input: mousedev - fix implicit conversion warning"):
> https://patchwork.kernel.org/patch/9753771/
> 

How does the warning catch a bug there?  While I do prefer the code
after the patch, wouldn't everything work just fine with "signed char
ps2[6]".

So it seems to me in that case (unlike KVM) the warning caught some ugly
code, but not a bug.  (In fact if there was a bug, it should have been
mentioned in the commit message, but it wasn't).

Paolo