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    SubjectRe: [PATCH v5 15/28] x86/arch_prctl: Create ARCH_GET_XSTATE/ARCH_PUT_XSTATE
    On Mon, May 24, 2021 at 07:10:57PM -0400, Len Brown wrote:
    > 1. CPUID has AMX
    > 2. XCR0 has AMX
    > 3. Linux permission has been requested and granted to this process

    Actually, you want *only* 3 as 1 is a bad idea - we're in this mess
    because userspace does feature detection on its own even when kernel
    support is needed.

    When Linux grants the permission, 1 and 2 should be implicitly given.

    > The dis-advantage of on-demand is that there is no buffer release mechanism --
    > the buffer lives as long as the task lives. Though, per previous conversation,
    > a future kernel could easily implement a buffer re-claim mechanism
    > behind the scenes
    > since the kernel is empowered to re-arm XFD for whatever reason it wants...

    Why is buffer release even needed? 1) sounds like a simple and clean thing to
    do.

    > 2. Synchronous allocation. Any task in the process that has AMX permission can
    > make a 2nd system call to request that the kernel synchronously allocate the
    > 8KB buffer for that task. *

    That doesn't sound as clean. More like unneeded work on the side of
    userspace programmer which she/he can save her-/himself from.

    Thx.

    --
    Regards/Gruss,
    Boris.

    https://people.kernel.org/tglx/notes-about-netiquette

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