Messages in this thread | | | From | Andy Lutomirski <> | Subject | Re: [PATCH v2 1/4] x86/fpu: Add kernel_fpu_begin_mask() to selectively initialize state | Date | Wed, 20 Jan 2021 04:19:24 -0800 |
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> On Jan 20, 2021, at 3:53 AM, Borislav Petkov <bp@alien8.de> wrote: > > On Tue, Jan 19, 2021 at 09:38:59AM -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 or need MXCSR initialized. >> _mmx_memcpy(), for example, can run before CR4.OSFXSR gets set, and >> initializing MXCSR will fail. >> >> - 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 >> what they want. > > Same nitpicks: > > https://lkml.kernel.org/r/20210119110834.GH27433@zn.tnic
I would have sworn I fixed those. Sorry!
> > -- > Regards/Gruss, > Boris. > > https://people.kernel.org/tglx/notes-about-netiquette
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