39a06b67c2
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 <marc.zyngier@arm.com> Signed-off-by: Will Deacon <will.deacon@arm.com> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> |
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.