Re: [Xen-devel] [PATCH for-4.5] xen/arm: Fix virtual timer on ARMv8 Model

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Ian,

On 27/11/14 10:40, Ian Campbell wrote:
> On Tue, 2014-11-25 at 17:44 +0000, Julien Grall wrote:
>> ARMv8 model may not disable correctly the timer interrupt when Xen
> 
> "correct disable"
> 
>> context switch to an idle vCPU. Therefore Xen may receive a spurious
> 
> "context switches" and s/spurious/unexpected/ (since spurious has a
> specific meaning in the h/w which does not match what is happening here)
> 
>> timer interrupt. As the idle domain doesn't have vGIC, Xen will crash
>> when trying to inject the interrupt with the following stack trace.
>>
>> (XEN)    [<0000000000228388>] _spin_lock_irqsave+0x28/0x94 (PC)
>> (XEN)    [<0000000000228380>] _spin_lock_irqsave+0x20/0x94 (LR)
>> (XEN)    [<0000000000250510>] vgic_vcpu_inject_irq+0x40/0x1b0
>> (XEN)    [<000000000024bcd0>] vtimer_interrupt+0x4c/0x54
>> (XEN)    [<0000000000247010>] do_IRQ+0x1a4/0x220
>> (XEN)    [<0000000000244864>] gic_interrupt+0x50/0xec
>> (XEN)    [<000000000024fbac>] do_trap_irq+0x20/0x2c
>> (XEN)    [<0000000000255240>] hyp_irq+0x5c/0x60
>> (XEN)    [<0000000000241084>] context_switch+0xb8/0xc4
>> (XEN)    [<000000000022482c>] schedule+0x684/0x6d0
>> (XEN)    [<000000000022785c>] __do_softirq+0xcc/0xe8
>> (XEN)    [<00000000002278d4>] do_softirq+0x14/0x1c
>> (XEN)    [<0000000000240fac>] idle_loop+0x134/0x154
>> (XEN)    [<000000000024c160>] start_secondary+0x14c/0x15c
>> (XEN)    [<0000000000000001>] 0000000000000001
>>
>> While we receive spurious virtual timer interrupt, this could be safely
>> ignore for the time being. A proper fix need to be found for Xen 4.6.
>>
>> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> 
> Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> 
> Although I wonder if we should log, perhaps rate limited or only once.

I don't think the printk is necessary, receiving this unexpected
interrupt is harmless from the perspective that the guest will still
work when the vCPU will run again.

> Also, I've some grammar nits (above and below) which I can fix on commit
> if there is no resend...

Thanks.

Regards,

-- 
Julien Grall

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