On 12/14/2023 1:01 AM, Chang S. Bae wrote:
On 12/13/2023 1:30 AM, Yang, Weijiang wrote:Let me involve Chang, the author of the code in question. Hi, Chang, In commit 70c3f1671b0c ("x86/fpu/xstate: Prepare XSAVE feature table for gaps in state component numbers"), you modified the loop as below: for (i = 0; i < ARRAY_SIZE(xsave_cpuid_features); i++) { - if (!boot_cpu_has(xsave_cpuid_features[i])) + unsigned short cid = xsave_cpuid_features[i]; + + /* Careful: X86_FEATURE_FPU is 0! */ + if ((i != XFEATURE_FP && !cid) || !boot_cpu_has(cid)) fpu_kernel_cfg.max_features &= ~BIT_ULL(i); } IMHO the change resulted functional change of the loop, i.e., before that only it only clears the bits without CPUIDs, but after the change, the side-effect of the loop will clear the bits of blank entries ( where xsave_cpuid_features[i] == 0 ) since the loop hits (i != XFEATURE_FP && !cid), is it intended or something else?The code was considered as much *simpler* than the other [1]. Yes, it clears those not listed in the table but they were either non-existed or disabled at that moment.
Thanks Chang, so I assume the "side-effect" is intended.
Thanks, Chang [1] https://lore.kernel.org/lkml/87y2eha576.fsf@xxxxxxxxxxxxxxxxxxxxxxx/
