From 39a06b67c2c1256bcf2361a1f67d2529f70ab206 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 18 Jul 2017 18:37:55 +0100 Subject: [PATCH] irqchip/gic: Ensure we have an ISB between ack and ->handle_irq Devices that expose their interrupt status registers via system registers (e.g. Statistical profiling, CPU PMU, DynamIQ PMU, arch timer, vgic (although unused by Linux), ...) rely on a context synchronising operation on the CPU to ensure that the updated status register is visible to the CPU when handling the interrupt. This usually happens as a result of taking the IRQ exception in the first place, but there are two race scenarios where this isn't the case. For example, let's say we have two peripherals (X and Y), where Y uses a system register for its interrupt status. Case 1: 1. CPU takes an IRQ exception as a result of X raising an interrupt 2. Y then raises its interrupt line, but the update to its system register is not yet visible to the CPU 3. The GIC decides to expose Y's interrupt number first in the Ack register 4. The CPU runs the IRQ handler for Y, but the status register is stale Case 2: 1. CPU takes an IRQ exception as a result of X raising an interrupt 2. CPU reads the interrupt number for X from the Ack register and runs its IRQ handler 3. Y raises its interrupt line and the Ack register is updated, but again, the update to its system register is not yet visible to the CPU. 4. Since the GIC drivers poll the Ack register, we read Y's interrupt number and run its handler without a context synchronisation operation, therefore seeing the stale register value. In either case, we run the risk of missing an IRQ. This patch solves the problem by ensuring that we execute an ISB in the GIC drivers prior to invoking the interrupt handler. This is already the case for GICv3 and EOIMode 1 (the usual case for the host). Cc: Marc Zyngier Signed-off-by: Will Deacon Signed-off-by: Marc Zyngier --- drivers/irqchip/irq-gic-v3.c | 2 ++ drivers/irqchip/irq-gic.c | 7 +++++-- 2 files changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/irqchip/irq-gic-v3.c b/drivers/irqchip/irq-gic-v3.c index 5ba64a7584a3..984c3ecfd22c 100644 --- a/drivers/irqchip/irq-gic-v3.c +++ b/drivers/irqchip/irq-gic-v3.c @@ -353,6 +353,8 @@ static asmlinkage void __exception_irq_entry gic_handle_irq(struct pt_regs *regs if (static_key_true(&supports_deactivate)) gic_write_eoir(irqnr); + else + isb(); err = handle_domain_irq(gic_data.domain, irqnr, regs); if (err) { diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c index 940c16278758..d3e7c43718b8 100644 --- a/drivers/irqchip/irq-gic.c +++ b/drivers/irqchip/irq-gic.c @@ -361,6 +361,7 @@ static void __exception_irq_entry gic_handle_irq(struct pt_regs *regs) if (likely(irqnr > 15 && irqnr < 1020)) { if (static_key_true(&supports_deactivate)) writel_relaxed(irqstat, cpu_base + GIC_CPU_EOI); + isb(); handle_domain_irq(gic->domain, irqnr, regs); continue; } @@ -401,10 +402,12 @@ static void gic_handle_cascade_irq(struct irq_desc *desc) goto out; cascade_irq = irq_find_mapping(chip_data->domain, gic_irq); - if (unlikely(gic_irq < 32 || gic_irq > 1020)) + if (unlikely(gic_irq < 32 || gic_irq > 1020)) { handle_bad_irq(desc); - else + } else { + isb(); generic_handle_irq(cascade_irq); + } out: chained_irq_exit(chip, desc); -- 2.20.1