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

[Ian Campbell <Ian.Campbell@citrix.com>]

On Thu, 2014-11-27 at 18:02 +0000, Julien Grall wrote:
> I propose to reword the commit message into:

You'll want to change the code comment too I think.

> 
> xen/arm: Handle platforms with edge-triggered virtual timer
> 
> Some platforms (such as the ARMv8 model) uses edge-triggered interrupt
> for the virtual timer. Even if the timer output signal is masked in the
> context switch, the GIC will keep track that of any raised interrupt
> while the IRQs has been disabled. As soon as the IRQs are re-enabled,
> the virtual interrupt timer will be injected to Xen.
> 
> The interrupt handler doesn't except to the receive the IRQ and will
> crash if an idle vCPU is running:
> 
> (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
> 
> The proper solution would be context/switching the virtual interrupt
> state at the GIC level. This would also avoid masking the output signal
> and requires specific handling in the guest OS.
> 
> Sadly, this solution require some refactoring which would miss the Xen
> 4.5 release.
> 
> For now implement a temporary solution which ignore the interrupt when
> the idle VCPU is running.
> 
> Regards,
>