On 04/06/15 11:46, Alex Bennée wrote: > > Marc Zyngier <marc.zyngier@xxxxxxx> writes: > >> On 04/06/15 11:20, Alex Bennée wrote: >>> >>> 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. >> >> Gahhh. You're right. I'm spending too much time on the VHE code these >> days. Guess I'll stick to the weasel words then. Can you respin it with >> Christoffer's comment addressed? > > Sure. Do you want it separated from the guest debug series or will you > be happy to take it with it when ready? I'll take it now, no need to wait on the whole debug series to fix this. 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
