Messages in this thread | | | Subject | Re: [PATCH v2] x86/fpu: copy MXCSR & MXCSR_FLAGS with SSE/YMM state | From | Rik van Riel <> | Date | Thu, 09 Feb 2017 20:00:11 -0500 |
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On Thu, 2017-02-09 at 16:45 -0800, Yu-cheng Yu wrote: > On Thu, Feb 09, 2017 at 06:43:47PM -0500, Rik van Riel wrote: > > /* > > + * Weird legacy quirk: SSE and YMM states store information in the > > + * MXCSR and MXCSR_FLAGS fields of the FP area. That means if the > > FP > > + * area is marked as unused in the xfeatures header, we need to > > copy > > + * MXCSR and MXCSR_FLAGS if either SSE or YMM are in use. > > + */ > > +static inline bool xfeatures_need_mxcsr_copy(u64 xfeatures) > > +{ > > + if (!(xfeatures & (XFEATURE_MASK_SSE|XFEATURE_MASK_YMM))) > > + return 0; > > + > > + if (xfeatures & XFEATURE_MASK_FP) > > + return 0; > > + > > + return 1; > > +} > > Would you consider separating MXCSR & MXCSR_FLAGS from > XFEATURE_MASK_FP. Here we assume if both xstate[0] and xstate[1] > are being copied, then there is no need to copy MXCSR/MXCSR_FLAGS > again. What if only xstate[0] is copied and MXCSR/MXCSR_FLAGS > is invalid?
Surely then the CPU would ignore the contents of MXCSR/MXCSR_FLAGS because the SSE and YMM bits in the xfeatures header are clear?
What am I missing?
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