Messages in this thread | | | Date | Fri, 10 Feb 2017 09:18:21 -0800 | From | Yu-cheng Yu <> | Subject | Re: [PATCH v2] x86/fpu: copy MXCSR & MXCSR_FLAGS with SSE/YMM state |
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On Thu, Feb 09, 2017 at 08:00:11PM -0500, Rik van Riel wrote: > 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?
For example in copy_user_to_xstate(), is it possible that only xstate[0] is copied in, but in fact the task already has a valid xstate[1] and MXCSR is overwritten? We can think about this as a separate patch.
Thanks, Yu-cheng
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