On Fri, 2012-06-01 at 18:39 +0200, Jan Kiszka wrote:
> On 2012-06-01 18:16, Alex Williamson wrote:
> > The kernel no longer allows us to pass NULL for a hard interrupt
> > handler without IRQF_ONESHOT. Should have been using this flag
> > anyway.
>
> This make the IRQ handling tail a bit slower (due to
> irq_finalize_oneshot). MSIs are edge-triggered, so there was no need for
> masking in theory.
Aren't these asynchronous since we can theoretically do
irq_finalize_oneshot while the guest is servicing the device?
> Hmm, can't we trust the information that an IRQ
> grabbed here is really a MSI type?
Apparently not, comment added with this check (1c6c6952):
* The interrupt was requested with handler = NULL, so
* we use the default primary handler for it. But it
* does not have the oneshot flag set. In combination
* with level interrupts this is deadly, because the
* default primary handler just wakes the thread, then
* the irq lines is reenabled, but the device still
* has the level irq asserted. Rinse and repeat....
*
* While this works for edge type interrupts, we play
* it safe and reject unconditionally because we can't
* say for sure which type this interrupt really
* has. The type flags are unreliable as the
* underlying chip implementation can override them.
Thanks,
Alex
> >
> > Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=43328
> >
> > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > ---
> >
> > virt/kvm/assigned-dev.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> > index 01f572c..e804d14 100644
> > --- a/virt/kvm/assigned-dev.c
> > +++ b/virt/kvm/assigned-dev.c
> > @@ -347,7 +347,7 @@ static int assigned_device_enable_host_msi(struct kvm *kvm,
> >
> > dev->host_irq = dev->dev->irq;
> > if (request_threaded_irq(dev->host_irq, NULL,
> > - kvm_assigned_dev_thread_msi, 0,
> > + kvm_assigned_dev_thread_msi, IRQF_ONESHOT,
> > dev->irq_name, dev)) {
> > pci_disable_msi(dev->dev);
> > return -EIO;
> > @@ -375,7 +375,7 @@ static int assigned_device_enable_host_msix(struct kvm *kvm,
> > for (i = 0; i < dev->entries_nr; i++) {
> > r = request_threaded_irq(dev->host_msix_entries[i].vector,
> > NULL, kvm_assigned_dev_thread_msix,
> > - 0, dev->irq_name, dev);
> > + IRQF_ONESHOT, dev->irq_name, dev);
> > if (r)
> > goto err;
> > }
> >
>
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