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Correct the description of check_cpu()

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check_cpu() turns on SSE instructions by clearing bit 15 of HWCR MSR
on legacy AMD processors. Refer to "MSRC001_0015 Hardware Configuration
(HWCR)" of BIOS and Kernel Developer Guide (BKDG) for AMD Family 14h
Models 00h-0Fh Processors [1].

[1] https://www.amd.com/system/files/TechDocs/43170_14h_Mod_00h-0Fh_BKDG.pdf
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Kagurazaka Kotori 2022-11-01 16:05:43 +08:00 committed by GitHub
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Booting/linux-bootstrap-2.md
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@ -358,7 +358,7 @@ if (cpu_level < req_level) {
}
```
The `check_cpu` function checks the CPU's flags, the presence of [long mode](http://en.wikipedia.org/wiki/Long_mode) in the case of x86_64(64-bit) CPU, checks the processor's vendor and makes preparations for certain vendors like turning off SSE+SSE2 for AMD if they are missing, etc.
The `check_cpu` function checks the CPU's flags, the presence of [long mode](http://en.wikipedia.org/wiki/Long_mode) in the case of x86_64(64-bit) CPU, checks the processor's vendor and makes preparations for certain vendors like turning on SSE+SSE2 for AMD if they are missing, etc.
at the next step, we may see a call to the `set_bios_mode` function after setup code found that a CPU is suitable. As we may see, this function is implemented only for the `x86_64` mode: