Re: [PATCH RFC v1 02/11] x86/fpu/xstate: Introduce xstate order table and accessor macro

[Ingo Molnar]

* Chang S. Bae <chang.seok.bae@xxxxxxxxx> wrote:

> > > I propose a new addition, an extension of functionality: if a new 
> > > CPUID bit indicates it, and a new MSR is written, XFEATURES bit 3 
> > > becomes active again - and the MPX area is now used by AVX. 
> > > Obviously only AVX-aware host and guest kernels would enable AVX.
> > 
> > Erm, s/AVX/APX ...
> 
> Just thought of another aspect of this:
> 
> I'm curious about how core dumps should handle this. Initially, an 
> xfeature mask was added to the software-reserved area [1] to indicate 
> which xfeatures were present in the layout. More recently, a new note 
> [2] was introduced to expose CPUID-reported size and offset 
> information, helping tools like GDB. From an offline interpretation 
> standpoint, I think these bits will become ambiguous without further 
> extensions.
> 
> [1] commit 5b3efd500854 ("x86, ptrace: regset extensions to support xstate")
> [2] commit ba386777a30b ("x86/elf: Add a new FPU buffer layout info to x86
> core files")

Okay, I guess I agree and you guys are right, the MPX/APX ambiguity is 
probably not worth it.

Still not happy about xfeature_noncompact_order[], but I guess that is 
the price if we want to reuse the MPX area. :-/

Thanks,

	Ingo