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Kernel: Manually reset the XCR0 register

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According to the Intel manual: "After reset, all bits (except bit 0) in
XCR0 are cleared to zero; XCR0[0] is set to 1."
Sadly we can't trust this, for example VirtualBox starts with
bits 0-4 set, so let's do it ourselves.

Fixes #5653
This commit is contained in:
Luke 2021-03-07 17:13:19 +00:00 committed by Andreas Kling
parent 5265a2d23e
commit 368f78d03c
Notes: sideshowbarker 2024-07-18 21:38:03 +09:00 
Author: https://github.com/Lubrsi
Commit: https://github.com/SerenityOS/serenity/commit/368f78d03c3
Pull-request: https://github.com/SerenityOS/serenity/pull/5684
Issue: https://github.com/SerenityOS/serenity/issues/5653
1 changed files with 10 additions and 3 deletions
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13
Kernel/Arch/i386/CPU.cpp
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@ -1033,11 +1033,18 @@ UNMAP_AFTER_INIT void Processor::cpu_setup()
write_cr4(read_cr4() | 0x4);
}
if (has_feature(CPUFeature::XSAVE) && has_feature(CPUFeature::AVX)) {
if (has_feature(CPUFeature::XSAVE)) {
// Turn on CR4.OSXSAVE
write_cr4(read_cr4() | 0x40000);
// Turn on AVX flags
write_xcr0(read_xcr0() | 0x7);
// According to the Intel manual: "After reset, all bits (except bit 0) in XCR0 are cleared to zero; XCR0[0] is set to 1."
// Sadly we can't trust this, for example VirtualBox starts with bits 0-4 set, so let's do it ourselves.
write_xcr0(0x1);
if (has_feature(CPUFeature::AVX)) {
// Turn on SSE, AVX and x87 flags
write_xcr0(read_xcr0() | 0x7);
}
}
}