On 1/10/2023 6:49 AM, Aaron Lewis wrote:
When I run xcr0_cpuid_test it fails because
xstate_get_guest_group_perm() reports partial support on SPR. It's
reporting 0x206e7 rather than the 0x6e7 I was hoping for. That's why
I went down the road of sanitizing xcr0. Though, if it's expected for
that to report something valid then sanitizing seems like the wrong
approach. If xcr0 is invalid it should stay invalid, and it should
cause a test to fail.
FWIW, we have this [1]:
/* Features which are dynamically enabled for a process on request */
#define XFEATURE_MASK_USER_DYNAMIC XFEATURE_MASK_XTILE_DATA
IOW, TILE_CFG is not part of the dynamic state. Because this state is
not XFD-supported, we can't enforce the state use. SDM has relevant text
here [2]:
"LDTILECFG and TILERELEASE initialize the TILEDATA state component. An
execution of either of these instructions does not generate #NM when
XCR0[18] = IA32_XFD[18] = 1; instead, it initializes TILEDATA normally.
(Note that STTILECFG does not use the TILEDATA state component. Thus, an
execution of this instruction does
not generate #NM when XCR0[18] = IA32_XFD[18] = 1.)"
Looking at how xstate_get_guest_group_perm() comes through with
invalid bits I came across this commit:
2308ee57d93d ("x86/fpu/amx: Enable the AMX feature in 64-bit mode")
- /* [XFEATURE_XTILE_DATA] = XFEATURE_MASK_XTILE, */
+ [XFEATURE_XTILE_DATA] = XFEATURE_MASK_XTILE_DATA,
Seems like it should really be:
+ [XFEATURE_XTILE_DATA] = XFEATURE_MASK_XTILE,
Thus, the change was intentional as far as I can remember.
Thank,
Chang
[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/x86/include/asm/fpu/xstate.h#n50
[2] SDM Vol 1. 13.14 Extended Feature Disable (XFD),
https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html
