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....@intel.com/
Yes, no mask in EDX:EAX works in such case. Thanks for pointing out the
patch.
BRs,
Jing
Thanks,
Chang
