linux-kernel - Re: Hang when booting guest kernels compiled with clang after SRSO mitigations

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Date:   Thu, 10 Aug 2023 09:14:14 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: Hang when booting guest kernels compiled with clang after SRSO
 mitigations

On Thu, Aug 10, 2023 at 08:48:31AM -0700, Nathan Chancellor wrote:
> On Thu, Aug 10, 2023 at 05:14:10PM +0200, Borislav Petkov wrote:
> > Also, can you bisect rc5..master to see which exact patch is causing
> > this?
> 
> Sure thing. I at least isolated it to the SRSO merge, so I will just
> bisect that to see the exact commit that causes this.

Heh, figured this would be the case:

# bad: [138bcddb86d8a4f842e4ed6f0585abc9b1a764ff] Merge tag 'x86_bugs_srso' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
# good: [14f9643dc90adea074a0ffb7a17d337eafc6a5cc] Merge tag 'wq-for-6.5-rc5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq
git bisect start '138bcddb86d8a4f842e4ed6f0585abc9b1a764ff' '14f9643dc90adea074a0ffb7a17d337eafc6a5cc'
# bad: [233d6f68b98d480a7c42ebe78c38f79d44741ca9] x86/srso: Add IBPB
git bisect bad 233d6f68b98d480a7c42ebe78c38f79d44741ca9
# bad: [fb3bd914b3ec28f5fb697ac55c4846ac2d542855] x86/srso: Add a Speculative RAS Overflow mitigation
git bisect bad fb3bd914b3ec28f5fb697ac55c4846ac2d542855
# good: [0e52740ffd10c6c316837c6c128f460f1aaba1ea] x86/bugs: Increase the x86 bugs vector size to two u32s
git bisect good 0e52740ffd10c6c316837c6c128f460f1aaba1ea
# first bad commit: [fb3bd914b3ec28f5fb697ac55c4846ac2d542855] x86/srso: Add a Speculative RAS Overflow mitigation

Not sure how helpful that will be...

Cheers,
Nathan