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

[Bhushan Bharat-R65777]

> -----Original Message-----
> From: Linuxppc-dev [mailto:linuxppc-dev-
> bounces+bharat.bhushan=freescale.com at lists.ozlabs.org] On Behalf 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). 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.


Another Question: 

The case is: 

Case 1)
 -> Local_irq_disable()  will set soft_enabled = 0
 -> Now Externel interrupt happens, there we set PACA_IRQ_EE in irq_happened, Also clears EE in SRR1 and rfi. So interrupts are hard disabled. No more other interrupt gated by MSR.EE can happen. Looks like the idea here is to not let a device keep on inserting interrupt till the interrupt condition on device is cleared, right?
 -> local_irq_enable() - This checks that irq_happened is set, and replays

Now the case 2)
Case 2)
-> Local_irq_disable()  will set soft_enabled = 0
 -> Now DEC interrupt happens. We set PACA_IRQ_DEC in irq_happened, But do not clear EE in SRR1 and rfi. So interrupts are not hard disabled. 
 -> Now say EE interrupt happens, there we set PACA_IRQ_EE in irq_happened, Also clears EE in SRR1 and rfi. So interrupts are hard disabled. 
 -> local_irq_enable() - This checks that irq_happened is set.
IIUC, it replays only one interrupt? is not it?

-Bharat