On 02/02/16 15:46, Christoffer Dall wrote:

On Tue, Feb 02, 2016 at 09:46:05AM +0000, Marc Zyngier wrote:

quoted

On 01/02/16 13:54, Christoffer Dall wrote:

quoted

On Mon, Jan 25, 2016 at 03:53:44PM +0000, Marc Zyngier wrote:

quoted

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.

Nothing goes away, but these registers do not get renamed either. For
example, TPIDR_EL1 doesn't magically access TPIDR_EL2 when running at
EL2+VHE, and there is no TPIDR_EL12 accessor either.

So TPIDR_EL1 is effectively "shared" between host and guest, and must be
save/restored (note that the host kernel still uses TIPDR_EL1 even when
running with VHE, and that KVM still uses TPIDR_EL2 to cache the current
vcpu).

quoted

quoted

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...

Does this make it clearer?

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...