Marc Zyngier <marc.zyngier@xxxxxxx> writes: > On 04/06/15 10:34, Christoffer Dall wrote: >> On Thu, May 28, 2015 at 10:43:06AM +0100, Alex Bennée wrote: >>> The elr_el2 and spsr_el2 registers in fact contain the processor state >>> before entry into the hypervisor code. >> >> be careful with your use of the hypervisor, in the KVM design the >> hypervisor is split across EL1 and EL2. "before entry into EL2." >> >>> In the case of guest state it >>> could be in either el0 or el1. >> >> true >> >>> >>> Signed-off-by: Alex Bennée <alex.bennee@xxxxxxxxxx> >>> --- >>> arch/arm64/kvm/hyp.S | 8 ++++---- >>> 1 file changed, 4 insertions(+), 4 deletions(-) >>> >>> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S >>> index d755922..1940a4c 100644 >>> --- a/arch/arm64/kvm/hyp.S >>> +++ b/arch/arm64/kvm/hyp.S >>> @@ -50,8 +50,8 @@ >>> stp x29, lr, [x3, #80] >>> >>> mrs x19, sp_el0 >>> - mrs x20, elr_el2 // EL1 PC >>> - mrs x21, spsr_el2 // EL1 pstate >>> + mrs x20, elr_el2 // PC before hyp entry >>> + mrs x21, spsr_el2 // pstate before hyp entry >>> >>> stp x19, x20, [x3, #96] >>> str x21, [x3, #112] >>> @@ -82,8 +82,8 @@ >>> ldr x21, [x3, #16] >>> >>> msr sp_el0, x19 >>> - msr elr_el2, x20 // EL1 PC >>> - msr spsr_el2, x21 // EL1 pstate >>> + msr elr_el2, x20 // PC to restore >>> + msr spsr_el2, x21 // pstate to restore >> >> I don't feel like 'to restore' is much more meaningful here. >> >> I would actually vote for removin the comments all together, since one >> should really understand the code as opposed to the comments when >> reading this kind of stuff. >> >> Meh, I'm not sure. Your patch is definitely better than doing nothing. >> >> Marc? > > While I definitely agree that people should pay more attention to the > code rather than blindly trusting comments, I still think there is some > value in disambiguating the exception entry/return, because this bit of > code assumes some intimate knowledge of the ARMv8 exception model. > > As for the comments themselves, I'd rather have some wording that > clearly indicate that we're dealing with guest information, i.e: > > mrs x20, elr_el2 // Guest PC > mrs x21, spsr_el2 // Guest pstate > > (and the same for the exception return). The "before hyp entry" and "to > restore" are not really useful (all the registers we are > saving/restoring fall into these categories). What I wanted to convey > here was that despite using an EL2 register, we are dealing with guest > registers. Which would be great it we were. However the code is used to save/restore the host context as well as the guest context hence my weasely words. > > Would this address your concerns? > > Thanks, > > M. -- Alex Bennée -- 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
