Messages in this thread | | | From | Len Brown <> | Date | Tue, 31 Aug 2021 18:07:23 -0400 | Subject | Re: [PATCH v9 12/26] x86/fpu/xstate: Use feature disable (XFD) to protect dynamic user state |
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On Mon, Aug 30, 2021 at 1:52 PM Borislav Petkov <bp@alien8.de> wrote:
> Well, if you preallocate everything...
Nothing prevents, say, a pthread_create() or anything else where the kernel consumes memory on behalf of a process from failing at run-time... AMX does not add a unique OOM risk here.
> > The advantage of the #NM over the syscall is that the programmer > > doesn't actually have to do anything. Also, transparently allocated > > buffers offer a theoretical benefit that a program may have many > > threads, but only a few may actually touch AMX, and so there is > > savings to be had by allocating buffers only for the threads that > > actually use the buffers. > > The program already asked the kernel whether it can use AMX - it can > allocate the buffers for the threads too.
The result is that if one thread in a 1,000 task process requests and touches AMX, the kernel would allocate 8MB, instead of 8KB of context switch buffers for that process, no?
Len Brown, Intel Open Source Technology Center
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