Re: Candidate Linux ABI for Intel AMX and hypothetical new related features

From: Thomas Gleixner
Date: Fri May 21 2021 - 17:43:45 EST

On Fri, May 21 2021 at 13:07, Andy Lutomirski wrote:
> On Fri, May 21, 2021, at 12:10 PM, Thomas Gleixner wrote:
>> Why? The bit can be enabled and #NM catches the violation of the ABI
>> contract if the application did not request usage. No XCR0 fiddling on
>> context switch required.
> XFD does nothing about signals.

It's a matter of what's implemented in #NM. XFD just arms #NM

> It also doesn’t help give applications a non-Linux-specific way to ask
> if AMX is available. The SDM says that one can read XCR0. Sure, we
> can use it, but cross platform libraries seem likely to get it wrong.

Well, that's the inevitable consequence of Intel declaring that
everything needs to be exposed unconditionally for the very wrong