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David Woodhouse 223ecac5f0 KVM: x86/xen: Allow 'out of range' event channel ports in IRQ routing table.
commit a7f4dff21f upstream.

To avoid imposing an ordering constraint on userspace, allow 'invalid'
event channel targets to be configured in the IRQ routing table.

This is the same as accepting interrupts targeted at vCPUs which don't
exist yet, which is already the case for both Xen event channels *and*
for MSIs (which don't do any filtering of permitted APIC ID targets at
all).

If userspace actually *triggers* an IRQ with an invalid target, that
will fail cleanly, as kvm_xen_set_evtchn_fast() also does the same range
check.

If KVM enforced that the IRQ target must be valid at the time it is
*configured*, that would force userspace to create all vCPUs and do
various other parts of setup (in this case, setting the Xen long_mode)
before restoring the IRQ table.

Cc: stable@vger.kernel.org
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>
Link: https://lore.kernel.org/r/e489252745ac4b53f1f7f50570b03fb416aa2065.camel@infradead.org
[sean: massage comment]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-07-17 18:32:07 +02:00
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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 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.