Subject: Re: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable interrupts

From: "tiejun.chen" <[email-masked]>
Date: Thu, 9 May 2013 16:04:48 +0800

On 05/09/2013 03:51 PM, Bhushan Bharat-R65777 wrote:
>
>
>> -----Original Message-----
>> From: tiejun.chen [mailto:[email-masked]]
>> Sent: Thursday, May 09, 2013 1:18 PM
>> To: Bhushan Bharat-R65777
>> Cc: Caraman Mihai Claudiu-B02008; Wood Scott-B07421; linuxppc-
>> [email-masked]; [email-masked]; [email-masked];
>> [email-masked]
>> Subject: Re: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable interrupts
>>
>> On 05/09/2013 03:33 PM, Bhushan Bharat-R65777 wrote:
>>>
>>>
>>>> -----Original Message-----
>>>> From: Linuxppc-dev [mailto:linuxppc-dev-
>>>> bounces+bharat.bhushan=[email-masked]] On Behalf Of
>>>> bounces+Caraman
>>>> Mihai Claudiu-B02008
>>>> Sent: Wednesday, May 08, 2013 6:44 PM
>>>> To: Wood Scott-B07421; tiejun.chen
>>>> Cc: [email-masked]; [email-masked];
>>>> [email-masked]; [email-masked]
>>>> Subject: RE: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable
>>>> interrupts
>>>>
>>>>>> This only disable soft interrupt for kvmppc_restart_interrupt()
>>>>>> that restarts interrupts if they were meant for the host:
>>>>>>
>>>>>> a. SOFT_DISABLE_INTS() only for BOOKE_INTERRUPT_EXTERNAL |
>>>>>> BOOKE_INTERRUPT_DECREMENTER | BOOKE_INTERRUPT_DOORBELL
>>>>>
>>>>> Those aren't the only exceptions that can end up going to the host.
>>>>> We could get a TLB miss that results in a heavyweight MMIO exit, etc.
>>>>>
>>>>>> And shouldn't we handle kvmppc_restart_interrupt() like the
>>>>>> original HOST flow?
>>>>>>
>>>>>> #define MASKABLE_EXCEPTION(trapnum, intnum, label, hdlr,
>>>>>> ack)           \
>>>>>>
>>>>>> START_EXCEPTION(label);                                         \
>>>>>>           NORMAL_EXCEPTION_PROLOG(trapnum, intnum,
>>>>>> PROLOG_ADDITION_MASKABLE)\
>>>>>>           EXCEPTION_COMMON(trapnum, PACA_EXGEN,
>>>>>> *INTS_DISABLE*)             \
>>>>>> 	...
>>>>>
>>>>> Could you elaborate on what you mean?
>>>>
>>>> I think Tiejun was saying that host has flags and replays only
>>>> EE/DEC/DBELL interrupts. There is special macro
>>>> masked_interrupt_book3e in those exception handlers that sets paca-
>>> irq_happened.
>>>>
>>>> The list of replied interrupts is limited to asynchronous noncritical
>>>> interrupts which can be masked by MSR[EE] (therefore no TLB miss).
>>>
>>> Embedded Perfmon interrupt is also asynchronous, Why that is not in the list
>> of masked interruts.
>>
>> Are you saying perfmon? If so, its also in that list:
>>
>>           START_EXCEPTION(perfmon);
>>           NORMAL_EXCEPTION_PROLOG(0x260, BOOKE_INTERRUPT_PERFORMANCE_MONITOR,
>>                                   PROLOG_ADDITION_NONE)
>>           EXCEPTION_COMMON(0x260, PACA_EXGEN, INTS_DISABLE)
>
> Where it is recorded in paca->irq_happned to be replayed later ?

In stead of PROLOG_ADDITION_MASKABLE, actually we have nothing to do with 
PROLOG_ADDITION_NONE for perfmon, so perfmon can be executed without lazy state.

Tiejun

>
>>
>> Tiejun
>>
>>>
>>> -Bharat
>>>
>>>> Now on KVM book3e we
>>>> don't want to put them in the irq_happened lazy state but rather to
>>>> execute them directly, so there is no reason for exception handling
>>>> symmetry between host and guest.
>>>>
>>>> -Mike
>>
>