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    SubjectRe: [PATCH v5 14/28] x86/fpu/xstate: Prevent unauthorised use of dynamic user state
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    On Jun 16, 2021, at 12:01, Dave Hansen <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.

    My apologies -- I neglect not to check the log immediately. XGETBV(1) took
    about 26 cycles on my test.

    Thanks,
    Chang

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