Messages in this thread | | | Subject | Re: [PATCH v5 14/28] x86/fpu/xstate: Prevent unauthorised use of dynamic user state | From | Dave Hansen <> | Date | Wed, 16 Jun 2021 12:28:54 -0700 |
| |
On 6/16/21 12:23 PM, Bae, Chang Seok wrote: > 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/
That's odd. How is it possible that the performance of XGETBV(1) informed the design of that patch without there being any mention of XGETBV in the comments or changelog?
| |