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Linux guests since commitb1c3497e60("x86/xen: Add support for HVMOP_set_evtchn_upcall_vector") in v6.0 onwards will use the per-vCPU upcall vector when it's advertised in the Xen CPUID leaves. This upcall is injected through the guest's local APIC as an MSI, unlike the older system vector which was merely injected by the hypervisor any time the CPU was able to receive an interrupt and the upcall_pending flags is set in its vcpu_info. Effectively, that makes the per-CPU upcall edge triggered instead of level triggered, which results in the upcall being lost if the MSI is delivered when the local APIC is *disabled*. Xen checks the vcpu_info->evtchn_upcall_pending flag when the local APIC for a vCPU is software enabled (in fact, on any write to the SPIV register which doesn't disable the APIC). Do the same in KVM since KVM doesn't provide a way for userspace to intervene and trap accesses to the SPIV register of a local APIC emulated by KVM. Fixes:fde0451be8("KVM: x86/xen: Support per-vCPU event channel upcall via local APIC") Signed-off-by: David Woodhouse <dwmw@amazon.co.uk> Reviewed-by: Paul Durrant <paul@xen.org> Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20240227115648.3104-3-dwmw2@infradead.org Signed-off-by: Sean Christopherson <seanjc@google.com>
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.