[PATCH v2 2/3] powerpc/64: enhance memcmp() with VMX instruction for long bytes comparision

[David Laight]

From: Simon Guo
> Sent: 27 September 2017 19:34
...
> > On X86 all the AVX registers are caller saved, the system call
> > entry could issue the instruction that invalidates them all.
> > Kernel code running in the context of a user process could then
> > use the registers without saving them.
> > It would only need to set a mark to ensure they are invalidated
> > again on return to user (might be cheap enough to do anyway).
> > Dunno about PPC though.
> 
> I am not aware of any ppc instruction which can set a "mark" or provide
> any high granularity flag against single or subgroup of vec regs' validity.
> But ppc experts may want to correct me.

I was just thinking of a software flag.

	David