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Oliver Upton 93078ae63f KVM: arm64: nv: Request vPE doorbell upon nested ERET to L2
Running an L2 guest with GICv4 enabled goes absolutely nowhere, and gets
into a vicious cycle of nested ERET followed by nested exception entry
into the L1.

When KVM does a put on a runnable vCPU, it marks the vPE as nonresident
but does not request a doorbell IRQ. Behind the scenes in the ITS
driver's view of the vCPU, its_vpe::pending_last gets set to true to
indicate that context is still runnable.

This comes to a head when doing the nested ERET into L2. The vPE doesn't
get scheduled on the redistributor as it is exclusively part of the L1's
VGIC context. kvm_vgic_vcpu_pending_irq() returns true because the vPE
appears runnable, and KVM does a nested exception entry into the L1
before L2 ever gets off the ground.

This issue can be papered over by requesting a doorbell IRQ when
descheduling a vPE as part of a nested ERET. KVM needs this anyway to
kick the vCPU out of the L2 when an IRQ becomes pending for the L1.

Link: https://lore.kernel.org/r/20240823212703.3576061-4-oliver.upton@linux.dev
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250225172930.1850838-13-maz@kernel.org
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
History 2025-03-03 14:57:10 -08:00
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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 reStructuredText 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.