Messages in this thread | | | From | "Bae, Chang Seok" <> | Subject | Re: [PATCH v5 14/28] x86/fpu/xstate: Prevent unauthorised use of dynamic user state | Date | Wed, 16 Jun 2021 19:23:45 +0000 |
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On Jun 16, 2021, at 12:01, Hansen, Dave <dave.hansen@intel.com> wrote: > On 6/16/21 11:47 AM, Bae, Chang Seok wrote: >> Reading XINUSE via XGETBV is cheap but not free. I don't know spending a >> hundred cycles for this WARN is big deal but this is one of the most >> performance-critical paths. > Is XGETBV(1) really a hundred cycles? That seems absurdly high for a > non-serializing register read.
This was checked to convince the benefit intended by PATCH25 -- https://lore.kernel.org/lkml/20210523193259.26200-26-chang.seok.bae@intel.com/
> If you're really worried, let's put it under X86_FEATURE_DEBUG_FPU or > something.
Yes. I will also make sure to include comments for this.
Thanks, Chang
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