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commit 464cb98f1c07298c4c10e714ae0c36338d18d316 upstream. Christoffer reports that on some implementations, writing to GICR_ISACTIVER0 (and similar GICD registers) can race badly with a guest issuing a deactivation of that interrupt via the system register interface. There are multiple reasons to this: - this uses an early write-acknoledgement memory type (nGnRE), meaning that the write may only have made it as far as some interconnect by the time the store is considered "done" - the GIC itself is allowed to buffer the write until it decides to take it into account (as long as it is in finite time) The effects are that the activation may not have taken effect by the time the kernel enters the guest, forcing an immediate exit, or that a guest deactivation occurs before the interrupt is active, doing nothing. In order to guarantee that the write to the ISACTIVER register has taken effect, read back from it, forcing the interconnect to propagate the write, and the GIC to process the write before returning the read. Reported-by: Christoffer Dall <christoffer.dall@arm.com> Signed-off-by: Marc Zyngier <maz@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Christoffer Dall <christoffer.dall@arm.com> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/all/20241106084418.3794612-1-maz@kernel.org Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.