linux-kernel - Re: [PATCH v2] x86/speculation: Use DECLARE_PER_CPU for x86_spec_ctrl

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Date:   Thu, 14 Jul 2022 15:14:53 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...e.de>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <llvm@...ts.linux.dev>,
        stable <stable@...r.kernel.org>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v2] x86/speculation: Use DECLARE_PER_CPU for x86_spec_ctrl_current

On Thu, Jul 14, 2022 at 2:56 PM Jakub Kicinski <kuba@...nel.org> wrote:
>
> I have clang 13, let me double check this fix is enough for the build
> to complete without disabling WERROR.

I have clang 14 locally, and it builds fine with that (and doesn't
build without it).

I actually normally build the kernel with both gcc and clang. My
"upstream" kernel I build with gcc, and then I have my "private random
collection of patches" kernel that I build with clang and that are
just rebased on top of the kernel-of-the-day.

This is all entirely for historical reasons - part of my "private
random collection of patches" used to be the "asm goto with outputs",
which had clang support first.

But then the reason I never even noticed the build breakage with the
retbleed patches until much too late was that those I just had as a
third fork off my upstream kernel, so despite me usually building with
clang too, that only got attention from gcc.

So it's really just a microcosm version of the exact same bigger issue
we always have with those embargoed hw security patches: they end up
missing out on all the usual test environments.

Anyway, I cherry-picked Nathan's patch from my clang tree and pushed
it out as commit db886979683a ("x86/speculation: Use DECLARE_PER_CPU
for x86_spec_ctrl_current").

                 Linus