Re: [PATCH v4 07/10] x86/xsaves: Fix PTRACE frames for XSAVES

[Yu-cheng Yu <yu-cheng.yu@intel.com>]

On Fri, Apr 29, 2016 at 03:36:12PM -0700, Dave Hansen wrote:
> On 04/29/2016 03:30 PM, Yu-cheng Yu wrote:
> > On Fri, Apr 29, 2016 at 01:25:34PM -0700, Dave Hansen wrote:
> >> On 03/04/2016 10:12 AM, Yu-cheng Yu wrote:
> >>> +	for (i = 0; i < XFEATURE_MAX; i++) {
> >>> +		/*
> >>> +		 * Copy only in-use xstates.
> >>> +		 */
> >>> +		if (((header.xfeatures >> i) & 1) && xfeature_enabled(i)) {
> >>> +			void *src = get_xsave_addr_no_check(xsave, i);
> >>
> >> How could a bit in header.xfeatures get set if it is not set in
> >> xfeature_enabled() aka xfeatures_mask aka XCR0?
> > 
> > Do you mean, we should test xfeature_enabled(i) first, like,
> > 
> > 	if (xfeature_enabled(i) && ((header.xfeatures >> i) & 1)) ?
> > 
> > The result will be the same, like you said, if XCR0[i] is not set,
> > hader.xfeatures[i] cannot be set.  But if XCR0[i] is set,
> > header.xfeatures[i] can be cleared. 
> 
> I think the xfeature_enabled(i) is probably redundant.  Does it serve
> any actual purpose?

Got it.