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

From: "tiejun.chen" <[email-masked]>
Date: Thu, 9 May 2013 15:47:50 +0800

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 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)

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