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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 14 Jul 2022 10:02:57 -0700
Message-ID: <CAHk-=wj4vtoWZPMXJU-B9qW1zLHsoA1Qb2P0NW=UFhZmrCrf9Q@mail.gmail.com>
Subject: Re: [PATCH 5.15 00/78] 5.15.55-rc1 review
To:     Boris Petkov <bp@alien8.de>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Guenter Roeck <linux@roeck-us.net>,
        Peter Zijlstra <peterz@infradead.org>,
        Thadeu Lima de Souza Cascardo <cascardo@canonical.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Naresh Kamboju <naresh.kamboju@linaro.org>,
        Florian Fainelli <f.fainelli@gmail.com>,
        kvm list <kvm@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        stable <stable@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Pavel Machek <pavel@denx.de>,
        Jon Hunter <jonathanh@nvidia.com>,
        Sudip Mukherjee <sudipm.mukherjee@gmail.com>,
        Slade Watkins <slade@sladewatkins.com>, patches@kernelci.org,
        Sean Christopherson <seanjc@google.com>,
        Shuah Khan <shuah@kernel.org>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, X86 ML <x86@kernel.org>,
        lkft-triage@lists.linaro.org,
        =?UTF-8?B?QWxleCBCZW5uw6ll?= <alex.bennee@linaro.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Anders Roxell <anders.roxell@linaro.org>
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On Thu, Jul 14, 2022 at 7:46 AM Boris Petkov <bp@alien8.de> wrote:
>
> On July 14, 2022 1:46:53 PM UTC, Paolo Bonzini <pbonzini@redhat.com> wrote:
> >Please leave that one out as Peter suggested a better fix and I have that queued for Linus.
>
> Already zapped.

I like Peter's more obvious use of FASTYOP_LENGTH, but this is just disgusting:

    #define FASTOP_SIZE (8 << ((FASTOP_LENGTH > 8) & 1) <<
((FASTOP_LENGTH > 16) & 1))

I mean, I understand what it's doing, but just two lines above it the
code has a "ilog2()" use that already depends on the fact that you can
use ilog2() as a constant compile-time expression.

And guess what? The code could just use roundup_pow_of_two(), which is
designed exactly like ilog2() to be used for compile-time constant
values.

So the code should just use

    #define FASTOP_SIZE roundup_pow_of_two(FASTOP_LENGTH)

and be a lot more legible, wouldn't it?

Because I don't think there is anything magical about the length
"8/16/32". It's purely "aligned and big enough to contain
FASTOP_LENGTH".

And then the point of that

    static_assert(FASTOP_LENGTH <= FASTOP_SIZE);

just goes away, because there are no subtle math issues there any more.

In fact, the remaining question is just "where did the 7 come from" in

    #define FASTOP_LENGTH (7 + ENDBR_INSN_SIZE + RET_LENGTH)

because other than that it all looks fairly straightforward.

              Linus