Messages in this thread | | | Date | Tue, 25 May 2021 19:27:05 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH v5 15/28] x86/arch_prctl: Create ARCH_GET_XSTATE/ARCH_PUT_XSTATE |
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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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