• Stefano Stabellini's avatar
    fix MSI injection on Xen · 428c3ece
    Stefano Stabellini authored
    On Xen MSIs can be remapped into pirqs, which are a type of event
    channels. It's mostly for the benefit of PCI passthrough devices, to
    avoid the overhead of interacting with the emulated lapic.
    
    However remapping interrupts and MSIs is also supported for emulated
    devices, such as the e1000 and virtio-net.
    
    When an interrupt or an MSI is remapped into a pirq, masking and
    unmasking is done by masking and unmasking the event channel. The
    masking bit on the PCI config space or MSI-X table should be ignored,
    but it isn't at the moment.
    
    As a consequence emulated devices which use MSI or MSI-X, such as
    virtio-net, don't work properly (the guest doesn't receive any
    notifications). The mechanism was working properly when xen_apic was
    introduced, but I haven't narrowed down which commit in particular is
    causing the regression.
    
    Fix the issue by ignoring the masking bit for MSI and MSI-X which have
    been remapped into pirqs.
    Signed-off-by: 's avatarStefano Stabellini <stefano.stabellini@eu.citrix.com>
    Reviewed-by: 's avatarMichael S. Tsirkin <mst@redhat.com>
    Signed-off-by: 's avatarMichael S. Tsirkin <mst@redhat.com>
    428c3ece
xen-hvm-stub.c 1.19 KB