selftests/x86/amx: Add test cases for AMX state management
AMX TILEDATA is a very large XSAVE feature. It could have caused
nasty XSAVE buffer space waste in two places:
* Signal stacks
* Kernel task_struct->fpu buffers
To avoid this waste, neither of these buffers have AMX state by
default. The non-default features are called "dynamic" features.
There is an arch_prctl(ARCH_REQ_XCOMP_PERM) which allows a task
to declare that it wants to use AMX or other "dynamic" XSAVE
features. This arch_prctl() ensures that sufficient sigaltstack
space is available before it will succeed. It also expands the
task_struct buffer.
Functions of this test:
* Test arch_prctl(ARCH_REQ_XCOMP_PERM). Ensure that it checks for
proper sigaltstack sizing and that the sizing is enforced for
future sigaltstack calls.
* Ensure that ARCH_REQ_XCOMP_PERM is inherited across fork()
* Ensure that TILEDATA use before the prctl() is fatal
* Ensure that TILEDATA is cleared across fork()
Note: Generally, compiler support is needed to do something with
AMX. Instead, directly load AMX state from userspace with a
plain XSAVE. Do not depend on the compiler.
[ dhansen: bunches of cleanups ]
Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20211026122524.7BEDAA95@davehans-spike.ostc.intel.com