linux-kernel - [PATCH v2] irqchip/sifive-plic: avoid interrupt ID 0 handling during suspend/resume

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Message-ID: <20250923144319.955868-1-lzampier@redhat.com>
Date: Tue, 23 Sep 2025 15:43:19 +0100
From: Lucas Zampieri <lzampier@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Lucas Zampieri <lzampier@...hat.com>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Samuel Holland <samuel.holland@...ive.com>,
	stable@...r.kernel.org,
	linux-riscv@...ts.infradead.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Jia Wang <wangjia@...rarisc.com>,
	Charles Mirabile <cmirabil@...hat.com>
Subject: [PATCH v2] irqchip/sifive-plic: avoid interrupt ID 0 handling during suspend/resume

According to the PLIC specification[1], global interrupt sources are
assigned small unsigned integer identifiers beginning at the value 1.
An interrupt ID of 0 is reserved to mean "no interrupt".

The current plic_irq_resume() and plic_irq_suspend() functions incorrectly
start the loop from index 0, which accesses the register space for the
reserved interrupt ID 0.

Change the loop to start from index 1, skipping the reserved
interrupt ID 0 as per the PLIC specification.

This prevents potential undefined behavior when accessing the reserved
register space during suspend/resume cycles.

Link: https://github.com/riscv/riscv-plic-spec/releases/tag/1.0.0

Fixes: e80f0b6a2cf3 ("irqchip/irq-sifive-plic: Add syscore callbacks for hibernation")
Co-developed-by: Jia Wang <wangjia@...rarisc.com>
Signed-off-by: Jia Wang <wangjia@...rarisc.com>
Co-developed-by: Charles Mirabile <cmirabil@...hat.com>
Signed-off-by: Charles Mirabile <cmirabil@...hat.com>
Signed-off-by: Lucas Zampieri <lzampier@...hat.com>
---
 drivers/irqchip/irq-sifive-plic.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/irqchip/irq-sifive-plic.c b/drivers/irqchip/irq-sifive-plic.c
index bf69a4802b71e..9c4af7d588463 100644
--- a/drivers/irqchip/irq-sifive-plic.c
+++ b/drivers/irqchip/irq-sifive-plic.c
@@ -252,7 +252,8 @@ static int plic_irq_suspend(void)
 
 	priv = per_cpu_ptr(&plic_handlers, smp_processor_id())->priv;
 
-	for (i = 0; i < priv->nr_irqs; i++) {
+	/* irq ID 0 is reserved */
+	for (i = 1; i < priv->nr_irqs; i++) {
 		__assign_bit(i, priv->prio_save,
 			     readl(priv->regs + PRIORITY_BASE + i * PRIORITY_PER_ID));
 	}
@@ -283,7 +284,8 @@ static void plic_irq_resume(void)
 
 	priv = per_cpu_ptr(&plic_handlers, smp_processor_id())->priv;
 
-	for (i = 0; i < priv->nr_irqs; i++) {
+	/* irq ID 0 is reserved */
+	for (i = 1; i < priv->nr_irqs; i++) {
 		index = BIT_WORD(i);
 		writel((priv->prio_save[index] & BIT_MASK(i)) ? 1 : 0,
 		       priv->regs + PRIORITY_BASE + i * PRIORITY_PER_ID);
-- 
2.51.0