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cpufeatures: check OS register support #919

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merged 5 commits into from
Jun 15, 2023
Merged

cpufeatures: check OS register support #919

merged 5 commits into from
Jun 15, 2023

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newpavlov
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@newpavlov newpavlov commented Jun 15, 2023 •
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newpavlov
newpavlov commented Jun 15, 2023
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cpufeatures/src/x86.rs Outdated Show resolved Hide resolved
@tarcieri
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It looks like you're using XGETBV without first checking CPUID to determine if it's available.

I was reading about some virtualized environments that didn't implement it yesterday (although I forget specifically which ones, maybe I can dig up a link)

@newpavlov
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I check it on line 76. Bit 26 of ECX register is responsible for availability of XSAVE, XRSTOR, XSETBV, XGETBV instructions.

@newpavlov
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According to this page, there are 3 bits relevant to AVX-512:

  • 5 opmask AVX-512 enabled and XSAVE support for opmask registers k0-k7
  • 6 ZMM_Hi256 AVX-512 enabled and XSAVE support for upper halves of lower ZMM registers
  • 7 Hi16_ZMM AVX-512 enabled and XSAVE support for upper ZMM registers

Honestly, I have no idea when we should check what. For now to be safe I will check all bits. We may change it in future according to user reports.

@newpavlov newpavlov merged commit 95219ac into master Jun 15, 2023
@newpavlov newpavlov deleted the xgetbv branch June 15, 2023 19:01
@newpavlov newpavlov mentioned this pull request Jul 5, 2023
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@tarcieri tarcieri tarcieri approved these changes

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cpufeatures: add XGETBV checks
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@newpavlov @tarcieri