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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: Mark McLoughlin <markmc@redhat.com>
Acked-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
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The ioapic acknowledge path translates interrupt vectors to irqs. It
currently uses a first match algorithm, stopping when it finds the first
redirection table entry containing the vector. That fails however if the
guest changes the irq to a different line, leaving the old redirection table
entry in place (though masked). Result is interrupts not making it to the
guest.
Fix by always scanning the entire redirection table.
Signed-off-by: Avi Kivity <avi@qumranet.com>
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There's a bug in the IOAPIC code for level-triggered interrupts. Its
relatively easy to trigger by sharing (virtio-blk + usbtablet was the
testcase, initially reported by Gerd von Egidy).
The "remote_irr" variable is used to indicate accepted but not yet acked
interrupts. Its cleared from the EOI handler.
Problem is that the EOI handler clears remote_irr unconditionally, even
if it reinjected another pending interrupt.
In that case, kvm_ioapic_set_irq() proceeds to ioapic_service() which
sets remote_irr even if it failed to inject (since the IRR was high due
to EOI reinjection).
Since the TMR bit has been cleared by the first EOI, the second one
fails to clear remote_irr.
End result is interrupt line dead.
Fix it by setting remote_irr only if a new pending interrupt has been
generated (and the TMR bit for vector in question set).
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
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Some Linux versions allow the timer interrupt to be processed by more than
one cpu, leading to hangs due to tsc instability. Work around the issue
by only disaptching the interrupt to vcpu 0.
Problem analyzed (and patch tested) by Sheng Yang.
Signed-off-by: Avi Kivity <avi@qumranet.com>
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Move ioapic code to common, since IA64 also needs it.
Signed-off-by: Zhang Xiantao <xiantao.zhang@intel.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>
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