linux-kernel - Re: [PATCH 1/1] drivers/perf: arm_pmu_acpi: avoid perf IRQ init when guest PMU is off

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Message-ID: <20170525152814.GR2859@arm.com>
Date:   Thu, 25 May 2017 16:28:14 +0100
From:   Will Deacon <will.deacon@....com>
To:     Wei Huang <wei@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        mark.rutland@....com
Subject: Re: [PATCH 1/1] drivers/perf: arm_pmu_acpi: avoid perf IRQ init when
 guest PMU is off

Hi Wei,

On Wed, May 24, 2017 at 09:36:41AM -0500, Wei Huang wrote:
> We saw perf IRQ init failures when running Linux kernel in an ACPI
> guest without PMU (i.e. pmu=off). This is because perf IRQ is not
> present when pmu=off, but arm_pmu_acpi still tries to register
> or unregister GSI. This patch addresses the problem by checking
> gicc->performance_interrupt. If it is 0, which is the value set
> by qemu when pmu=off, we skip the IRQ register/unregister process.
> 
> [    4.069470] bc00: 0000000000040b00 ffff0000089db190
> [    4.070267] [<ffff000008134f80>] enable_percpu_irq+0xdc/0xe4
> [    4.071192] [<ffff000008667cc4>] arm_perf_starting_cpu+0x108/0x10c
> [    4.072200] [<ffff0000080cbdd4>] cpuhp_invoke_callback+0x14c/0x4ac
> [    4.073210] [<ffff0000080ccd3c>] cpuhp_thread_fun+0xd4/0x11c
> [    4.074132] [<ffff0000080f1394>] smpboot_thread_fn+0x1b4/0x1c4
> [    4.075081] [<ffff0000080ec90c>] kthread+0x10c/0x138
> [    4.075921] [<ffff0000080833c0>] ret_from_fork+0x10/0x50
> [    4.076947] genirq: Setting trigger mode 4 for irq 43 failed
> (gic_set_type+0x0/0x74)
> 
> Signed-off-by: Wei Huang <wei@...hat.com>
> ---
>  drivers/perf/arm_pmu_acpi.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/perf/arm_pmu_acpi.c b/drivers/perf/arm_pmu_acpi.c
> index 34c862f..d6bb75d 100644
> --- a/drivers/perf/arm_pmu_acpi.c
> +++ b/drivers/perf/arm_pmu_acpi.c
> @@ -29,6 +29,9 @@ static int arm_pmu_acpi_register_irq(int cpu)
>  		return -EINVAL;
>  
>  	gsi = gicc->performance_interrupt;
> +	if (!gsi)
> +		return 0;

So a GSI of zero means we return an IRQ of zero, which correctly gets
treated as "No ACPI PMU"...

>  	if (gicc->flags & ACPI_MADT_PERFORMANCE_IRQ_MODE)
>  		trigger = ACPI_EDGE_SENSITIVE;
>  	else
> @@ -58,7 +61,8 @@ static void arm_pmu_acpi_unregister_irq(int cpu)
>  		return;
>  
>  	gsi = gicc->performance_interrupt;
> -	acpi_unregister_gsi(gsi);
> +	if (gsi)
> +		acpi_unregister_gsi(gsi);

... but then I don't see how we can get here, so I'll drop this hunk.

Will