Messages in this thread | | | Date | Sat, 27 Feb 2016 14:13:37 +0100 | From | Borislav Petkov <> | Subject | Re: [lkp] [x86/fpu] 58122bf1d8: WARNING: CPU: 0 PID: 1 at arch/x86/include/asm/fpu/internal.h:529 fpu__restore+0x28f/0x9ab() |
| |
On Sat, Feb 27, 2016 at 01:02:11PM +0100, Ingo Molnar wrote: > So I'm wondering, why did this commit: > > 58122bf1d856 x86/fpu: Default eagerfpu=on on all CPUs >
Hmm, so looking at switch_fpu_prepare():
/* * If the task has used the math, pre-load the FPU on xsave processors * or if the past 5 consecutive context-switches used math. */ fpu.preload = static_cpu_has(X86_FEATURE_FPU) && new_fpu->fpstate_active && (use_eager_fpu() || new_fpu->counter > 5); ^^^^^^^^^^^^^^
and later:
if (old_fpu->fpregs_active) {
...
/* Don't change CR0.TS if we just switch! */ if (fpu.preload) { ... __fpregs_activate(new_fpu);
so I can see a possible link between 58122bf1d856 and what we're seeing.
But as I've told you offlist, I couldn't confirm that this commit was the culprit due to my simulated reproducer. So I'm thinking the 0day guys have a more reliable one.
> trigger the warning, while it never triggered on CPUs that were already > eagerfpu=on for years?
That I can't explain... yet.
FWIW, the one time splat I saw, happened on an IVB machine on 32-bit which has always been eagerfpu=on.
> There must be something we are still missing I think.
Yeah.
-- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply.
| |