[PATCH v2 3/6] x86/hyperv: Fix usage of cpu_online_mask to get valid cpu

[Michael Kelley]

From: Nuno Das Neves <nunodasneves at linux.microsoft.com> Sent: Thursday, July 3, 2025 3:45 PM
> 
> Accessing cpu_online_mask here is problematic because the cpus read lock
> is not held in this context.
> 
> However, cpu_online_mask isn't needed here since the effective affinity
> mask is guaranteed to be valid in this callback. So, just use
> cpumask_first() to get the cpu instead of ANDing it with cpus_online_mask
> unnecessarily.
> 
> Fixes: e39397d1fd68 ("x86/hyperv: implement an MSI domain for root partition")
> Reported-by: Michael Kelley <mhklinux at outlook.com>
> Closes: https://lore.kernel.org/linux-hyperv/SN6PR02MB4157639630F8AD2D8FD8F52FD475A@SN6PR02MB4157.namprd02.prod.outlook.com/
> Suggested-by: Thomas Gleixner <tglx at linutronix.de>
> Signed-off-by: Nuno Das Neves <nunodasneves at linux.microsoft.com>
> ---
>  arch/x86/hyperv/irqdomain.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/arch/x86/hyperv/irqdomain.c b/arch/x86/hyperv/irqdomain.c
> index 31f0d29cbc5e..e28c317ac9e8 100644
> --- a/arch/x86/hyperv/irqdomain.c
> +++ b/arch/x86/hyperv/irqdomain.c
> @@ -192,7 +192,6 @@ static void hv_irq_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
>  	struct pci_dev *dev;
>  	struct hv_interrupt_entry out_entry, *stored_entry;
>  	struct irq_cfg *cfg = irqd_cfg(data);
> -	const cpumask_t *affinity;
>  	int cpu;
>  	u64 status;
> 
> @@ -204,8 +203,7 @@ static void hv_irq_compose_msi_msg(struct irq_data *data, struct msi_msg *msg)
>  		return;
>  	}
> 
> -	affinity = irq_data_get_effective_affinity_mask(data);
> -	cpu = cpumask_first_and(affinity, cpu_online_mask);
> +	cpu = cpumask_first(irq_data_get_effective_affinity_mask(data));
> 
>  	if (data->chip_data) {
>  		/*
> --
> 2.34.1

Reviewed-by: Michael Kelley <mhklinux at outlook.com>