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? > > 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
