Re: [PATCH v4 14/22] x86/fpu/xstate: Expand the xstate buffer on the first use of dynamic user state

[Liu, Jing2]

> > > For AMX, we must still reserve the space, but we are not going to write zeros
> > > for clean state.  We so this in software by checking XINUSE=0, and clearing
> > > the xstate_bf for the XSAVE.  As a result, for XINUSE=0, we can skip
> > > writing the zeros, even though we can't compress the space.
> > So my understanding is that clearing xstate_bv will not help prevent saving
> > zeros, but only not masking EDX:EAX, since the following logic. Not sure if
> > this is just what you mean. :)
> FWIW, PATCH21 [1] uses the instruction mask to skip writing zeros on sigframe.
> Then, XSAVE will clear the xstate_bv for the xtile data state bit.
>
> [1] https://lore.kernel.org/lkml/20210221185637.19281-22-chang.seok.bae@xxxxxxxxx/
Yes, no mask in EDX:EAX works in such case. Thanks for pointing out the 
patch.

BRs,
Jing
> Thanks,
> Chang