Re: [PATCH v4 0/10] x86/xsaves: Fix XSAVES known issues

[Yu-cheng Yu]

On Fri, Apr 29, 2016 at 11:09:23AM -0700, Dave Hansen wrote:

> Once we *HAVE* XSAVES support, it also opens up the possibilities for
> doing things like dynamic XSAVE buffer allocation.  For instance, let
> threads that are not _using_ AVX-512 not waste the 2k of space for it.

If we can somehow modify exec* system call to scan the executable binary (in user space) and pass along a bitmask containing xfeatures used in the binary, and XSAVES is enabled in the kernel, we can easily save a lot of memory.  The kernel only needs to allocate space for tasks that actually use xstates; most of them do not.