Re: [Xen-devel] [PATCH V7 1/3] x86/xsaves: fix overwriting between non-lazy/lazy xsaves

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 31.03.16 at 10:57, <shuai.ruan@xxxxxxxxxxxxxxx> wrote:
> +#define XRSTOR(pfx) \
> +        if ( v->arch.xcr0_accum & XSTATE_XSAVES_ONLY ) \
> +        { \
> +            if ( unlikely(!(ptr->xsave_hdr.xcomp_bv & \
> +                            XSTATE_COMPACTION_ENABLED)) ) \
> +                ptr->xsave_hdr.xcomp_bv |= ptr->xsave_hdr.xstate_bv | \
> +                                           XSTATE_COMPACTION_ENABLED; \

From v5 to v6 this changed from just = to |=, without any
explanation, and without me really noticing - why? Weren't
the other changes done specifically to guarantee xcomp_bv
to be zero up to this point? In which case I'd prefer to make
this obvious/explicit, by using = and perhaps an ASSERT()
here. (I have a patch ready, but I'd like to understand if
there was a reason for this change that I don't see.)

Jan


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