Re: [Xen-devel] [PATCH V6 1/2] x86/xsaves: calculate the comp_offsets base on xcomp_bv

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 24.03.16 at 09:29, <shuai.ruan@xxxxxxxxxxxxxxx> wrote:
>  static void *get_xsave_addr(struct xsave_struct *xsave,
> -        unsigned int xfeature_idx)
> +                            const uint16_t *comp_offsets,
> +                            unsigned int xfeature_idx)
>  {
>      if ( !((1ul << xfeature_idx) & xsave->xsave_hdr.xstate_bv) )
>          return NULL;

While not a problem in this patch, I think this being at least
questionable now becomes more obvious: With XSAVEC and
XSAVES this field may have clear bits just because the
component was in init state. Yet I don't think this should be
fixed here - instead the consumer(s) should better deal with
NULL coming back here (i.e. expand_xsave_states() should
probably memset() the area in an "else" to the if() leading to
memcpy(), whereas compress_xsave_states() is fine as is).

That's a 3rd patch, though.

> +    return (void *)xsave + (xsave_area_compressed(xsave) ?
> +                            comp_offsets[xfeature_idx] :
> +                            xstate_offsets[xfeature_idx]);

This function doesn't ever get called when
!xsave_area_compressed(xsave), so I don't really see why this
conditional expression ever got added. Yet another follow-up
patch I would say.

The patch here looks okay to me now.

Jan


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