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

From: "tiejun.chen" <[email-masked]>
Date: Tue, 7 May 2013 09:56:25 +0800

On 05/07/2013 07:50 AM, Scott Wood wrote:
> On 05/05/2013 10:13:17 PM, tiejun.chen wrote:
>> On 05/06/2013 11:10 AM, Tiejun Chen wrote:
>>> For the external interrupt, the decrementer exception and the doorbell
>>> excpetion, we also need to soft-disable interrupts while doing as host
>>> interrupt handlers since the DO_KVM hook is always performed to skip
>>> EXCEPTION_COMMON then miss this original chance with the 'ints' (INTS_DISABLE).
>
> http://patchwork.ozlabs.org/patch/241344/
> http://patchwork.ozlabs.org/patch/241412/
>
> :-)

I'm observing the same behaviour as well:

	WARN_ON_ONCE(!irqs_disabled());

>
>>> Signed-off-by: Tiejun Chen <[email-masked]>
>>> ---
>>>   arch/powerpc/kvm/bookehv_interrupts.S |    9 +++++++++
>>>   1 file changed, 9 insertions(+)
>>>
>>> diff --git a/arch/powerpc/kvm/bookehv_interrupts.S
>>> b/arch/powerpc/kvm/bookehv_interrupts.S
>>> index e8ed7d6..2fd62bf 100644
>>> --- a/arch/powerpc/kvm/bookehv_interrupts.S
>>> +++ b/arch/powerpc/kvm/bookehv_interrupts.S
>>> @@ -33,6 +33,8 @@
>>>
>>>   #ifdef CONFIG_64BIT
>>>   #include <asm/exception-64e.h>
>>> +#include <asm/hw_irq.h>
>>> +#include <asm/irqflags.h>
>>>   #else
>>>   #include "../kernel/head_booke.h" /* for THREAD_NORMSAVE() */
>>>   #endif
>>> @@ -469,6 +471,13 @@ _GLOBAL(kvmppc_resume_host)
>>>       PPC_LL    r3, HOST_RUN(r1)
>>>       mr    r5, r14 /* intno */
>>>       mr    r14, r4 /* Save vcpu pointer. */
>>> +#ifdef CONFIG_64BIT
>>> +    /* Should we soft-disable interrupts? */
>>> +    andi.    r6, r5, BOOKE_INTERRUPT_EXTERNAL | BOOKE_INTERRUPT_DECREMENTER
>>> | BOOKE_INTERRUPT_DOORBELL
>>> +    beq    skip_soft_dis
>>> +    SOFT_DISABLE_INTS(r7,r8)
>>> +skip_soft_dis:
>>> +#endif
>
> Why wouldn't we always disable them?  kvmppc_handle_exit() will enable
> interrupts when it's ready.

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

b. bl      kvmppc_handle_exit

c. kvmppc_handle_exit()
{
         int r = RESUME_HOST;
         int s;

         /* update before a new last_exit_type is rewritten */
         kvmppc_update_timing_stats(vcpu);

         /* restart interrupts if they were meant for the host */
         kvmppc_restart_interrupt(vcpu, exit_nr);

         local_irq_enable();	==> Enable again.
....

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*)             \
	...

So I think this should be reasonable :)

Tiejun