Re: [Xen-devel] [PATCH] xen/arm: Fix smp_send_call_function_mask() for current CPU

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Hi Anup,
thanks for the patch.


On Thu, 14 Aug 2014, Anup Patel wrote:
> The smp_send_call_function_mask() does not work on Foundation v8
> model with one CPU. The reason being gicv2_send_SGI() is called
> with irqmode==SGI_TARGET_LIST and *cpu_mask=0x1 on CPU0 which
> does not work on Foundation v8 model.

I read the GIC spec again, and this has to be a bug in the Foundation v8
model. Please make sure to raise this issue with ARM so that they can
fix it.


> Further, it is really strange that smp_send_call_function_mask()
> depends on GIC SGIs for calling function on current CPU.
> 
> This patch fixes smp_send_call_function_mask() for current CPU
> by directly calling smp_call_function_interrupt() on current CPU.
> This is very similar to what Xen x86 does.

It could be a reasonable improvement regardless of the Foundation v8
bug. I would recommend to:

- Avoid mentioning the bug in the Foundation model in the commit
message, because a bug in an emulator is not a good reason to make
changes in Xen. If that was the only reason, then we would need to
introduce the change as a per-platform quirk, like
PLATFORM_QUIRK_GIC_64K_STRIDE.

- Clear the smp_processor_id() bit from mask, otherwise we end up
calling the function twice on the processor we are running on at the
moment.



> Signed-off-by: Anup Patel <anup.patel@xxxxxxxxxx>
> Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@xxxxxxxxxx>
> ---
>  xen/arch/arm/smp.c |    7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/xen/arch/arm/smp.c b/xen/arch/arm/smp.c
> index 30203b8..4fde3f9 100644
> --- a/xen/arch/arm/smp.c
> +++ b/xen/arch/arm/smp.c
> @@ -20,6 +20,13 @@ void smp_send_event_check_mask(const cpumask_t *mask)
>  void smp_send_call_function_mask(const cpumask_t *mask)
>  {
>      send_SGI_mask(mask, GIC_SGI_CALL_FUNCTION);
> +
> +    if ( cpumask_test_cpu(smp_processor_id(), mask) )
> +    {
> +        local_irq_disable();
> +        smp_call_function_interrupt();
> +        local_irq_enable();
> +    }
>  }
>  
>  /*
> -- 
> 1.7.9.5
> 

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