Re: [PATCH v2 10/21] arm64: KVM: VHE: Split save/restore of sysregs shared between EL1 and EL2

[Christoffer Dall]

On Tue, Feb 02, 2016 at 09:46:05AM +0000, Marc Zyngier wrote:
> On 01/02/16 13:54, Christoffer Dall wrote:
> > On Mon, Jan 25, 2016 at 03:53:44PM +0000, Marc Zyngier wrote:
> >> A handful of system registers are still shared between EL1 and EL2,
> >> even while using VHE. These are tpidr*_el[01], actlr_el1, sp0, elr,
> >> and spsr.
> > 
> > So by shared registers you mean registers that do both have an EL0/1
> > version as well as an EL2 version, but where accesses aren't rewritten
> > transparently?
> 
> No, I mean that these registers do *not* have a separate banked version.
> There is only a single set of registers, which have to be save/restored
> the old way.

huh, ARMv8 clearly specifies the existence of TPIDR_EL0, TPIDR_EL1, and
TPIDR_EL2, for example.

I cannot seem to find anywhere in the VHE spec that says that the
TPIDR_EL2 goes away.  I'm confused now.

> 
> > 
> > also, by sp0 do you mean sp_el0, and by elr you mean elr_el1, and by
> > spsr you mean spsr_el1 ?
> 
> sp0 -> sp_el0 indeed. elr and spsr really are the guest PC and PSTATE,
> so I should really reword this commit message, it is utterly confusing.
> 
I guess I don't understand the definition of a 'shared' register given
your comments here...

Thanks,
-Christoffer