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

[Bae, Chang Seok]

On Mar 24, 2021, at 22:12, Liu, Jing2 <jing2.liu@xxxxxxxxxxxxxxx> wrote:
> On 3/25/2021 5:09 AM, Len Brown wrote:
>> 
>> 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/

Thanks,
Chang