>> The fix I am proposing is... >> >> state->xsave.header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT | >> xfeatures_mask; > > Actually I thought about this change before I made this patch, but I don't > this > is the right fix. It is always error prone to init the xcomp_bv to all the > supported feature. In case like copyin_to_xsaves(), it is possible that the > features which should be set in xcomp_bv do not equal to all the supported > features. Please see the following codes in copyin_to_xsaves(): > /* > * The state that came in from userspace was user-state only. > * Mask all the user states out of 'xfeatures': > */ > xsave->header.xfeatures &= XFEATURE_MASK_SUPERVISOR; > > /* > * Add back in the features that came in from userspace: > */ > xsave->header.xfeatures |= xfeatures;
Hi Kevin, I think you may be confusing 'xfeatures' with 'xcomp_bv'. xfeatures tells you what features are present in the buffer while xcomp_bv tells you what *format* the buffer is in. Userspace never dictates the *format* of the kernel buffer, only the contents of each state. So, it makes sense that the copyin code would not (and should not) modify xcomp_bv. We ensure that xcomp_bv has all supported states set all the time, or we're *supposed* to.
