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Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines

From Ingo Molnar <mingo@kernel.org>
Newsgroups linux.kernel
Subject Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines
Date 2016-03-12 16:20 +0100
Message-ID <rbTuG-847-21@gated-at.bofh.it> (permalink)
References (5 earlier) <rbt7d-5b2-47@gated-at.bofh.it> <rbtqx-5pl-1@gated-at.bofh.it> <rbtAe-5vz-15@gated-at.bofh.it> <rbA8G-1R9-25@gated-at.bofh.it> <rbDpT-4rR-3@gated-at.bofh.it>
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* Borislav Petkov <bp@alien8.de> wrote:

> On Fri, Mar 11, 2016 at 10:32:43AM -0800, Linus Torvalds wrote:
> > Obvious Ack to the patch, along with a "how did this ever work
> > before?" comment..
> 
> I had a sarcastic sentence in the commit message which I deleted later:
> 
> "Apparently no one had tried the kernel on a 486er after the FPU
> rewrite. Backwards compatibility is overrated."
> 
> :-)
> 
> I'm still wondering, though, why didn't the Quark people scream
> earlier... And who knows, it was probably b0rked even before the
> FPU rewrite.

So I actually tested legacy FPU support during (and after) the big FPU rewrite - I 
even tried FPU emu and we made that work (it was broken for like years).

This particular breakage was made prominent recently, with switching old FPU CPUs 
over to eagerfpu context switching:

  58122bf1d856 x86/fpu: Default eagerfpu=on on all CPUs

If you check the fix, it only affects eagerfpu code paths. So to see the bug with 
Quark (or ancient CPUs) you'd have to have booted it with eagerfpu=on - and most 
people avoid twiddling boot parameters if they can avoid it.

Thanks,

	Ingo

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Thread

Got FPU related warning on Intel Quark during boot Andy Shevchenko <andy.shevchenko@gmail.com> - 2016-03-10 11:50 +0100
  Re: Got FPU related warning on Intel Quark during boot Ingo Molnar <mingo@kernel.org> - 2016-03-10 12:20 +0100
    Re: Got FPU related warning on Intel Quark during boot Andy Shevchenko <andy.shevchenko@gmail.com> - 2016-03-10 13:50 +0100
      Re: Got FPU related warning on Intel Quark during boot Borislav Petkov <bp@alien8.de> - 2016-03-10 14:00 +0100
        Re: Got FPU related warning on Intel Quark during boot Andy Shevchenko <andy.shevchenko@gmail.com> - 2016-03-10 14:40 +0100
          Re: Got FPU related warning on Intel Quark during boot Borislav Petkov <bp@alien8.de> - 2016-03-10 16:10 +0100
            Re: Got FPU related warning on Intel Quark during boot Andy Shevchenko <andy.shevchenko@gmail.com> - 2016-03-10 16:30 +0100
              Re: Got FPU related warning on Intel Quark during boot Bryan O'Donoghue <pure.logic@nexus-software.ie> - 2016-03-10 16:50 +0100
                Re: Got FPU related warning on Intel Quark during boot Borislav Petkov <bp@alien8.de> - 2016-03-10 17:50 +0100
                Re: Got FPU related warning on Intel Quark during boot Bryan O'Donoghue <pure.logic@nexus-software.ie> - 2016-03-10 18:20 +0100
                Re: Got FPU related warning on Intel Quark during boot Borislav Petkov <bp@alien8.de> - 2016-03-10 20:10 +0100
                Re: Got FPU related warning on Intel Quark during boot Andy Lutomirski <luto@amacapital.net> - 2016-03-11 02:40 +0100
                Re: Got FPU related warning on Intel Quark during boot Bryan O'Donoghue <pure.logic@nexus-software.ie> - 2016-03-11 12:00 +0100
            Re: Got FPU related warning on Intel Quark during boot Andy Lutomirski <luto@amacapital.net> - 2016-03-11 02:50 +0100
              Re: Got FPU related warning on Intel Quark during boot Ingo Molnar <mingo@kernel.org> - 2016-03-11 10:10 +0100
                Re: Got FPU related warning on Intel Quark during boot Borislav Petkov <bp@alien8.de> - 2016-03-11 10:50 +0100
                Re: Got FPU related warning on Intel Quark during boot Bryan O'Donoghue <pure.logic@nexus-software.ie> - 2016-03-11 12:10 +0100
                Re: Got FPU related warning on Intel Quark during boot Borislav Petkov <bp@alien8.de> - 2016-03-11 12:30 +0100
                [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Borislav Petkov <bp@alien8.de> - 2016-03-11 12:40 +0100
                Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Linus Torvalds <torvalds@linux-foundation.org> - 2016-03-11 19:40 +0100
                Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Dave Hansen <dave.hansen@linux.intel.com> - 2016-03-11 23:10 +0100
                Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Borislav Petkov <bp@alien8.de> - 2016-03-11 23:30 +0100
                Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Andy Lutomirski <luto@amacapital.net> - 2016-03-12 18:30 +0100
                Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Borislav Petkov <bp@alien8.de> - 2016-03-12 18:50 +0100
                Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Borislav Petkov <bp@alien8.de> - 2016-03-11 23:10 +0100
                Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Bryan O'Donoghue <pure.logic@nexus-software.ie> - 2016-03-12 13:10 +0100
                Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Borislav Petkov <bp@alien8.de> - 2016-03-12 13:30 +0100
                Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Ingo Molnar <mingo@kernel.org> - 2016-03-12 16:20 +0100
                Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Ingo Molnar <mingo@kernel.org> - 2016-03-12 16:10 +0100
                Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Ingo Molnar <mingo@kernel.org> - 2016-03-12 16:20 +0100
                [tip:x86/urgent] x86/fpu: Fix eager-FPU handling on legacy FPU  machines tip-bot for Borislav Petkov <tipbot@zytor.com> - 2016-03-12 16:20 +0100

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