linux-kernel - [PATCH v2 3/6] x86/hyperv: Fix usage of cpu_online

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Message-Id: <1751582677-30930-4-git-send-email-nunodasneves@linux.microsoft.com>
Date: Thu,  3 Jul 2025 15:44:34 -0700
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: linux-hyperv@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org,
	mhklinux@...look.com,
	tglx@...utronix.de,
	bhelgaas@...gle.com,
	romank@...ux.microsoft.com
Cc: kys@...rosoft.com,
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	Nuno Das Neves <nunodasneves@...ux.microsoft.com>
Subject: [PATCH v2 3/6] x86/hyperv: Fix usage of cpu_online_mask to get valid cpu

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@...look.com>
Closes: https://lore.kernel.org/linux-hyperv/SN6PR02MB4157639630F8AD2D8FD8F52FD475A@SN6PR02MB4157.namprd02.prod.outlook.com/
Suggested-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Nuno Das Neves <nunodasneves@...ux.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