On 02/02/16 15:46, Christoffer Dall wrote: > 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. 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). >> >>> >>> 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... -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
