linux-kernel - Re: [PATCH 5.15 00/78] 5.15.55-rc1 review

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Message-ID: <7b3ccb3e-174b-6f31-d875-452082262906@redhat.com>
Date:   Fri, 15 Jul 2022 13:35:16 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Boris Petkov <bp@...en8.de>, Guenter Roeck <linux@...ck-us.net>,
        Thadeu Lima de Souza Cascardo <cascardo@...onical.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        kvm list <kvm@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        stable <stable@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Pavel Machek <pavel@...x.de>,
        Jon Hunter <jonathanh@...dia.com>,
        Sudip Mukherjee <sudipm.mukherjee@...il.com>,
        Slade Watkins <slade@...dewatkins.com>, patches@...nelci.org,
        Sean Christopherson <seanjc@...gle.com>,
        Shuah Khan <shuah@...nel.org>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
        lkft-triage@...ts.linaro.org,
        Alex Bennée <alex.bennee@...aro.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Anders Roxell <anders.roxell@...aro.org>
Subject: Re: [PATCH 5.15 00/78] 5.15.55-rc1 review

On 7/14/22 20:16, Linus Torvalds wrote:
> Oh, btw, how bad would it be to just do
> 
>      #define FASTOP_SIZE 16
>      static_assert(FASTOP_SIZE >= FASTOP_LENGTH)

Yeah, for 32 I might have some (probably irrational) qualms, but 16 is 
not worth the trouble.

Given 3 bytes for ENDBR, 5 for the return thunk and 1 for the straight 
line speculation INT3, there are 7 bytes left and only 4 are currently 
used (for instructions encoded as "66 0f xx xx").  So FASTOP_SIZE at 
SETCC_ALIGN can indeed be 16 unconditionally.

Paolo