linux-kernel - Re: [PATCH 2/2] misc: Register a PPI for the vcpu stall detection virtual device

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Date: Fri, 24 May 2024 20:00:42 +0100
From: Conor Dooley <conor@...nel.org>
To: Sebastian Ene <sebastianene@...gle.com>
Cc: arnd@...db.de, gregkh@...uxfoundation.org, will@...nel.org,
	maz@...nel.org, Rob Herring <robh+dt@...nel.org>,
	Dragan Cvetic <dragan.cvetic@...inx.com>,
	Guenter Roeck <linux@...ck-us.net>, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH 2/2] misc: Register a PPI for the vcpu stall detection
 virtual device

On Thu, May 23, 2024 at 04:04:13PM +0000, Sebastian Ene wrote:
> Request a PPI for each vCPU during probe which will be used by the host
> to communicate a stall detected event on the vCPU. When the host raises
> this interrupt from the virtual machine monitor, the guest is expected to
> handle the interrupt and panic.
> 
> Signed-off-by: Sebastian Ene <sebastianene@...gle.com>
> ---
>  drivers/misc/vcpu_stall_detector.c | 41 ++++++++++++++++++++++++++++--
>  1 file changed, 39 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/misc/vcpu_stall_detector.c b/drivers/misc/vcpu_stall_detector.c
> index e2015c87f03f..c580cd7fd225 100644
> --- a/drivers/misc/vcpu_stall_detector.c
> +++ b/drivers/misc/vcpu_stall_detector.c
> @@ -32,6 +32,7 @@
>  struct vcpu_stall_detect_config {
>  	u32 clock_freq_hz;
>  	u32 stall_timeout_sec;
> +	int ppi_irq;
>  
>  	void __iomem *membase;
>  	struct platform_device *dev;
> @@ -77,6 +78,12 @@ vcpu_stall_detect_timer_fn(struct hrtimer *hrtimer)
>  	return HRTIMER_RESTART;
>  }
>  
> +static irqreturn_t vcpu_stall_detector_irq(int irq, void *dev)
> +{
> +	panic("vCPU stall detector");
> +	return IRQ_HANDLED;
> +}
> +
>  static int start_stall_detector_cpu(unsigned int cpu)
>  {
>  	u32 ticks, ping_timeout_ms;
> @@ -132,7 +139,7 @@ static int stop_stall_detector_cpu(unsigned int cpu)
>  
>  static int vcpu_stall_detect_probe(struct platform_device *pdev)
>  {
> -	int ret;
> +	int ret, irq, num_irqs;
>  	struct resource *r;
>  	void __iomem *membase;
>  	u32 clock_freq_hz = VCPU_STALL_DEFAULT_CLOCK_HZ;
> @@ -169,9 +176,32 @@ static int vcpu_stall_detect_probe(struct platform_device *pdev)
>  	vcpu_stall_config = (struct vcpu_stall_detect_config) {
>  		.membase		= membase,
>  		.clock_freq_hz		= clock_freq_hz,
> -		.stall_timeout_sec	= stall_timeout_sec
> +		.stall_timeout_sec	= stall_timeout_sec,
> +		.ppi_irq		= -1,
>  	};
>  
> +	num_irqs = platform_irq_count(pdev);
> +	if (num_irqs < 0) {
> +		dev_err(&pdev->dev, "Failed to get irqs\n");

platform_irq_count() either returns a number or EPROBE_DEFER, I don't
think emitting an error on deferred probe is the correct thing to do
here?

> +		ret = num_irqs;
> +		goto err;
> +	} else if (num_irqs > 1) {
> +		dev_err(&pdev->dev, "Multipple irqs detected\n");

Typo. I don't really see why you're going to this level of complexity
though, why aren't you just doing a single get_irq_optional()?

> +		ret = -EINVAL;
> +		goto err;
> +	} else if (num_irqs == 1) {
> +		irq = platform_get_irq(pdev, 0);
> +		if ((irq > 0) && irq_is_percpu_devid(irq)) {
> +			ret = request_percpu_irq(irq,
> +						 vcpu_stall_detector_irq,
> +						 "vcpu_stall_detector",
> +						 vcpu_stall_detectors);
> +			if (!ret)
> +				vcpu_stall_config.ppi_irq = irq;
> +
> +		}
> +	}
> +
>  	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
>  				"virt/vcpu_stall_detector:online",
>  				start_stall_detector_cpu,
> @@ -184,6 +214,9 @@ static int vcpu_stall_detect_probe(struct platform_device *pdev)
>  	vcpu_stall_config.hp_online = ret;
>  	return 0;
>  err:
> +	if (vcpu_stall_config.ppi_irq > 0)
> +		free_percpu_irq(vcpu_stall_config.ppi_irq,
> +				vcpu_stall_detectors);
>  	return ret;
>  }
>  
> @@ -193,6 +226,10 @@ static void vcpu_stall_detect_remove(struct platform_device *pdev)
>  
>  	cpuhp_remove_state(vcpu_stall_config.hp_online);
>  
> +	if (vcpu_stall_config.ppi_irq > 0)
> +		free_percpu_irq(vcpu_stall_config.ppi_irq,
> +				vcpu_stall_detectors);
> +
>  	for_each_possible_cpu(cpu)
>  		stop_stall_detector_cpu(cpu);
>  }
> -- 
> 2.45.1.288.g0e0cd299f1-goog
> 
> 

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