Re: [PATCH 03/18] KVM: ARM64: Add offset defines for PMU registers

[Shannon Zhao <shannon.zhao@linaro.org>]

On 2015/7/17 18:17, Christoffer Dall wrote:
> On Fri, Jul 17, 2015 at 04:25:06PM +0800, Shannon Zhao wrote:
>>
>>
>> On 2015/7/17 2:45, Christoffer Dall wrote:
>>> On Mon, Jul 06, 2015 at 10:17:33AM +0800, shannon.zhao@linaro.org wrote:
>>>> From: Shannon Zhao <shannon.zhao@linaro.org>
>>>>
>>>> We are about to trap and emulate acccesses to each PMU register
>>>> individually. This adds the context offsets for the AArch64 PMU
>>>> registers and their AArch32 counterparts.
>>>>
>>>> Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
>>>> ---
>>>>   arch/arm64/include/asm/kvm_asm.h | 59 +++++++++++++++++++++++++++++++++++-----
>>>>   1 file changed, 52 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
>>>> index 3c5fe68..21b5d3b 100644
>>>> --- a/arch/arm64/include/asm/kvm_asm.h
>>>> +++ b/arch/arm64/include/asm/kvm_asm.h
>>>> @@ -56,14 +56,36 @@
>>>>   #define DBGWVR15_EL1	86
>>>>   #define MDCCINT_EL1	87	/* Monitor Debug Comms Channel Interrupt Enable Reg */
>>>>
>>>> +/* Performance Monitors Registers */
>>>> +#define PMCR_EL0	88	/* Control Register */
>>>> +#define PMOVSSET_EL0	89	/* Overflow Flag Status Set Register */
>>>> +#define PMOVSCLR_EL0	90	/* Overflow Flag Status Clear Register */
>>>> +#define PMCCNTR_EL0	91	/* Cycle Counter Register */
>>>> +#define PMSELR_EL0	92	/* Event Counter Selection Register */
>>>> +#define PMCEID0_EL0	93	/* Common Event Identification Register 0 */
>>>> +#define PMCEID1_EL0	94	/* Common Event Identification Register 1 */
>>>> +#define PMEVCNTR0_EL0	95	/* Event Counter Register (0-30) */
>>>
>>> why do we need these when we trap-and-emulate and we have the kvm_pmc
>>> structs?
>> This just makes the guest work when accessing these registers.
>>
>>> Is that because the kvm_pmc structs are only used when we
>>> actually have an active counter running and registered with perf?
>>>
>>
>> Right, the kvm_pmc structs are used to store the status of perf evnets,
>> like the event type, count number of this perf event.
>>
>> On the other hand, the kernel perf codes will not directly access to the
>> PMEVCNTRx_EL0 and PMEVTYPERx_EL0 registers. It will firstly write the
>> index of select counter to PMSELR_EL0 and access to PMXEVCNTR_EL0 or
>> PMXEVTYPER_EL0. Then this is architecturally mapped to PMEVCNTRx_EL0 and
>> PMEVTYPERx_EL0.
>>
>
> I'm just wondering if it makes sense to keep virtual state around for
> all these registers, since we don't emulate the counter values, so why
> do we need to preserve any virtual cpu state for all of them?
>

Good point. Will remove this :)

Thanks,
-- 
Shannon