Messages in this thread | | | Date | Tue, 19 Jan 2021 12:08:34 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH 1/4] x86/fpu: Add kernel_fpu_begin_mask() to selectively initialize state |
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Just nitpicks:
On Sun, Jan 17, 2021 at 10:20:38PM -0800, Andy Lutomirski wrote: > Currently, requesting kernel FPU access doesn't distinguish which parts of > the extended ("FPU") state are needed. This is nice for simplicity, but > there are a few cases in which it's suboptimal: > > - The vast majority of in-kernel FPU users want XMM/YMM/ZMM state but do > not use legacy 387 state. These users want MXCSR initialized but don't > care about the FPU control word. Skipping FNINIT would save time. > (Empirically, FNINIT is several times slower than LDMXCSR.) > > - Code that wants MMX doesn't want need MXCSR or FCW initialized.
"want/need" ?
> _mmx_memcpy(), for example, can run before CR4.OSFXSR gets set, and > initializing MXCSR will fail.
"... because LDMXCSR generates an #UD when the aforementioned CR4 bit is not set."
> - Any future in-kernel users of XFD (eXtended Feature Disable)-capable > dynamic states will need special handling. > > This patch adds a more specific API that allows callers specify exactly
s/This patch adds/Add/
> what they want.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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