Re: [REGRESSION] 4.2-rc2: early boot memory corruption from FPU rework

From	Linus Torvalds <torvalds@linux-foundation.org>
Newsgroups	linux.kernel
Subject	Re: [REGRESSION] 4.2-rc2: early boot memory corruption from FPU rework
Date	2015-07-16 04:40 +0200
Message-ID	<pMHfA-1FU-5@gated-at.bofh.it> (permalink)
References	<pmPiq-1Qw-7@gated-at.bofh.it> <pmPit-1Qw-61@gated-at.bofh.it> <pMeng-1AT-19@gated-at.bofh.it> <pMsJz-5F0-5@gated-at.bofh.it> <pMFns-7jk-17@gated-at.bofh.it>
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On Wed, Jul 15, 2015 at 5:34 PM, Dave Hansen
<dave.hansen@linux.intel.com> wrote:
>
> The old code sized the buffer in a fully architectural way and it
> worked.  The CPU *tells* you how much memory the 'xsave' instruction is
> going to scribble on.  The new code just merrily calls it and let it
> scribble away.  This is as clear-cut a regression as I've ever seen.

Yes, I think we'll need to revert it, or do something else drastic
like make that initial fp state allocation *much* bigger and then have
a "disable xsaves if if it's still not big enough".

setup_xstate_features() should be able to easily just say "this was
the maximum offset+size we saw", and we can take that to either do a
proper allocation, or verify that the static allocation is indeed big
enough.

Apparently a straight revert doesn't work, if only because things in
that area have been renamed very aggressively (both files and
functions and variables). Ingo?

            Linus
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Thread

4.2-rc2: early boot memory corruption from FPU rework Dave Hansen <dave.hansen@linux.intel.com> - 2015-07-14 21:50 +0200
  Re: 4.2-rc2: early boot memory corruption from FPU rework "H. Peter Anvin" <hpa@zytor.com> - 2015-07-15 03:30 +0200
  Re: 4.2-rc2: early boot memory corruption from FPU rework Ingo Molnar <mingo@kernel.org> - 2015-07-15 13:10 +0200
    [REGRESSION] 4.2-rc2: early boot memory corruption from FPU rework Dave Hansen <dave.hansen@linux.intel.com> - 2015-07-16 02:40 +0200
      Re: [REGRESSION] 4.2-rc2: early boot memory corruption from FPU rework Linus Torvalds <torvalds@linux-foundation.org> - 2015-07-16 04:40 +0200
      Re: [REGRESSION] 4.2-rc2: early boot memory corruption from FPU rework Linus Torvalds <torvalds@linux-foundation.org> - 2015-07-16 05:00 +0200
      Re: [REGRESSION] 4.2-rc2: early boot memory corruption from FPU  rework Ingo Molnar <mingo@kernel.org> - 2015-07-17 09:50 +0200
        Re: [REGRESSION] 4.2-rc2: early boot memory corruption from FPU  rework Ingo Molnar <mingo@kernel.org> - 2015-07-17 11:00 +0200

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