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

From: Linus Torvalds
Date: Fri Mar 11 2016 - 13:32:51 EST

On Fri, Mar 11, 2016 at 3:32 AM, Borislav Petkov <bp@xxxxxxxxx> wrote:
> 486 cores like Intel Quark support only the very old, legacy x87 FPU
> (FSAVE/FRSTOR, CPUID bit FXSR is not set). And our FPU code wasn't
> handling the saving and restoring there properly. First, Andy Shevchenko
> reported a splat:
> WARNING: CPU: 0 PID: 823 at arch/x86/include/asm/fpu/internal.h:163 fpu__clear+0x8c/0x160
> which was us trying to execute FXRSTOR on those machines even though
> they don't support it.
> After taking care of that, Bryan O'Donoghue reported that a simple FPU
> test still failed because we weren't initializing the FPU state properly
> on those machines.

Obvious Ack to the patch, along with a "how did this ever work
before?" comment..