On Thu, Nov 08, 2018 at 12:40:02PM -0800, Yu-cheng Yu wrote:
> In fpu_init_system_xstate(), we test and clear features that are not enabled.
> There we depend on the order of these elements. This is the tenth "unknown
> xstate feature".
Aha, those are *reserved* bits - not unused, in XCR0.
Do an s/unused/reserved/g pls.
Now let's see, you have 0 for the 10th bit which happens to be
#define X86_FEATURE_FPU ( 0*32+ 0) /* Onboard FPU */
too. And if we look at the code:
for (i = 0; i < ARRAY_SIZE(xsave_cpuid_features); i++) {
if (!boot_cpu_has(xsave_cpuid_features[i]))
xfeatures_mask_all &= ~BIT_ULL(i);
guess what happens if i == 10.
I know, the subsequent & SUPPORTED_XFEATURES_MASK saves you from the
#GP but that's still not good enough. The loop should not even call
boot_cpu_has() for reserved feature bits.
Thx.
--
Regards/Gruss,
Boris.
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