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

[Bhushan Bharat-R65777]

> -----Original Message-----
> From: tiejun.chen [mailto:tiejun.chen at windriver.com]
> Sent: Thursday, May 09, 2013 1:48 PM
> To: Bhushan Bharat-R65777
> Cc: Kevin Hao; Caraman Mihai Claudiu-B02008; kvm at vger.kernel.org; Wood Scott-
> B07421; agraf at suse.de; kvm-ppc at vger.kernel.org; linuxppc-dev at lists.ozlabs.org
> Subject: Re: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable interrupts
> 
> On 05/09/2013 04:12 PM, Bhushan Bharat-R65777 wrote:
> >
> >
> >> -----Original Message-----
> >> From: Kevin Hao [mailto:haokexin at gmail.com]
> >> Sent: Thursday, May 09, 2013 1:38 PM
> >> To: Bhushan Bharat-R65777
> >> Cc: tiejun.chen; Caraman Mihai Claudiu-B02008; kvm at vger.kernel.org;
> >> Wood Scott- B07421; agraf at suse.de; kvm-ppc at vger.kernel.org;
> >> linuxppc-dev at lists.ozlabs.org
> >> Subject: Re: [RFC][KVM][PATCH 1/1] kvm:ppc:booke-64: soft-disable
> >> interrupts
> >>
> >> On Thu, May 09, 2013 at 07:51:09AM +0000, Bhushan Bharat-R65777 wrote:
> >>>
> >>>
> >>>> -----Original Message-----
> >>>> From: tiejun.chen [mailto:tiejun.chen at windriver.com]
> >>>> Sent: Thursday, May 09, 2013 1:18 PM
> >>>> To: Bhushan Bharat-R65777
> >>>> Cc: Caraman Mihai Claudiu-B02008; Wood Scott-B07421; linuxppc-
> >>>> dev at lists.ozlabs.org; agraf at suse.de; kvm-ppc at vger.kernel.org;
> >>>> kvm at vger.kernel.org
> >>>> 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=freescale.com at lists.ozlabs.org] On Behalf
> >>>>>> bounces+Of Caraman
> >>>>>> Mihai Claudiu-B02008
> >>>>>> Sent: Wednesday, May 08, 2013 6:44 PM
> >>>>>> To: Wood Scott-B07421; tiejun.chen
> >>>>>> Cc: linuxppc-dev at lists.ozlabs.org; agraf at suse.de;
> >>>>>> kvm-ppc at vger.kernel.org; kvm at vger.kernel.org
> >>>>>> 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 ?
> >>
> >> Actually we don't want replay the perfmon interrupt later. We would
> >> run it even soft irq is disabled and just treat it as NMI. Please see
> >> the following function quoted from arch/powerpc/perf/core-fsl-emb.c:
> >>    /*
> >>     * If interrupts were soft-disabled when a PMU interrupt occurs, treat
> >>     * it as an NMI.
> >>     */
> >>    static inline int perf_intr_is_nmi(struct pt_regs *regs)
> >>    {
> >>    #ifdef __powerpc64__
> >>            return !regs->softe;
> >>    #else
> >>            return 0;
> >>    #endif
> >>    }
> >
> > Is it because that we cannot afford to lose perfmon interrupt for more
> accurate capturing of data ?
> 
>      powerpc/perf: e500 support
> 
>      This implements perf_event support for the Freescale embedded performance
>      monitor, based on the existing perf_event.c that supports server/classic
>      chips.
> 
>      Some limitations:
>      - Performance monitor interrupts are regular EE interrupts, and thus you
>        can't profile places with interrupts disabled.  We may want to implement
>        soft IRQ-disabling, with perfmon interrupts exempted and treated as NMIs.

Ahh, that gives the answer and same as I expected :)

-Bharat

> 
> Tiejun
> 
> >
> > -Bharat
> >
> >>
> >> Thanks,
> >> Kevin
> >>
> >>>
> >>>>
> >>>> 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
> >>>>
> >>>
> >>> _______________________________________________
> >>> Linuxppc-dev mailing list
> >>> Linuxppc-dev at lists.ozlabs.org
> >>> https://lists.ozlabs.org/listinfo/linuxppc-dev
> >
> >
> >
>