Messages in this thread | | | Date | Thu, 24 Aug 2023 19:58:42 +0800 | From | Feng Tang <> | Subject | Re: [PATCH] x86/fpu: set X86_FEATURE_OSXSAVE feature after enabling OSXSAVE in CR4 |
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Hi Thomas,
On Thu, Aug 24, 2023 at 11:01:18AM +0200, Thomas Gleixner wrote: > On Wed, Aug 23 2023 at 14:57, Feng Tang wrote: > > diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c > > index 0bab497c9436..8ebea0d522d2 100644 > > --- a/arch/x86/kernel/fpu/xstate.c > > +++ b/arch/x86/kernel/fpu/xstate.c > > @@ -173,6 +173,9 @@ void fpu__init_cpu_xstate(void) > > > > cr4_set_bits(X86_CR4_OSXSAVE); > > > > + if (!boot_cpu_has(X86_FEATURE_OSXSAVE)) > > + setup_force_cpu_cap(X86_FEATURE_OSXSAVE); > > This is wrong in several aspects: > > 1) You force the feature bit _before_ XSAVE is completely > initialized. fpu__init_system_xstate() has error paths which > disable XSAVE.
Yes, I missed the error path in BSP fpu initialization code.
> 2) This conditional should have been a red flag for you simply > because fpu__init_cpu_xstate() is invoked on all CPUs not only > on the BSP.
Indeed. when I worked on the patch, I even thought about ugly thing like:
if (raw_smp_processor_id() == 0) setup_force_cpu_cap(X86_FEATURE_OSXSAVE); > I fixed it up and added a proper comment explaining it.
Thanks for fixing it up and improving the comments!
- Feng
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