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

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On 05/09/2013 04:23 PM, Bhushan Bharat-R65777 wrote:


-----Original Message-----
From: Linuxppc-dev [mailto:linuxppc-dev-
bounces+bharat.bhushan=freescale.com@xxxxxxxxxxxxxxxx] On Behalf Of Caraman
Mihai Claudiu-B02008
Sent: Wednesday, May 08, 2013 6:44 PM
To: Wood Scott-B07421; tiejun.chen
Cc: linuxppc-dev@xxxxxxxxxxxxxxxx; agraf@xxxxxxx; kvm-ppc@xxxxxxxxxxxxxxx;
kvm@xxxxxxxxxxxxxxx
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:


Actually in the case GS=1 even if EE=0, EXT/DEC/DBELL still occur as I recall.

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?

I don't understand "the interrupt condition on device is cleared" here.

I think regardless if you clear the device interrupt status, the system still receive a pending interrupt once EE or GS = 1.

  -> local_irq_enable() - This checks that irq_happened is set, and replays

ret_from_except also check to replay.


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?

After anyone is replayed in arch_local_irq_restore(), we will set soft/hard interrupt there:

set_soft_enabled(1);
__hard_irq_enable();

Then any pending interrupt can be executed now.

Additionally, ret_from_except probably check to replay all.

Tiejun
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