• Mark McLoughlin's avatar
    KVM: IOAPIC: Fix level-triggered irq injection hang · 35baff25
    Mark McLoughlin authored
    The "remote_irr" variable is used to indicate an interrupt
    which has been received by the LAPIC, but not acked.
    
    In our EOI handler, we unset remote_irr and re-inject the
    interrupt if the interrupt line is still asserted.
    
    However, we do not set remote_irr here, leading to a
    situation where if kvm_ioapic_set_irq() is called, then we go
    ahead and call ioapic_service(). This means that IRR is
    re-asserted even though the interrupt is currently in service
    (i.e. LAPIC IRR is cleared and ISR/TMR set)
    
    The issue with this is that when the currently executing
    interrupt handler finishes and writes LAPIC EOI, then TMR is
    unset and EOI sent to the IOAPIC. Since IRR is now asserted,
    but TMR is not, then when the second interrupt is handled,
    no EOI is sent and if there is any pending interrupt, it is
    not re-injected.
    
    This fixes a hang only seen while running mke2fs -j on an
    8Gb virtio disk backed by a fully sparse raw file, with
    aliguori "avoid fragmented virtio-blk transfers by copying"
    changes.
    Signed-off-by: default avatarMark McLoughlin <markmc@redhat.com>
    Acked-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
    Signed-off-by: default avatarAvi Kivity <avi@qumranet.com>
    35baff25
ioapic.c 9.75 KB