Re: [PATCH v4 3/9] KVM: Clear assigned guest IRQ on release

Avi Kivity
2010-11-09T10:58:29Z

On 11/08/2010 01:21 PM, Jan Kiszka wrote:
> When we deassign a guest IRQ, clear the potentially asserted guest line.
> There might be no chance for the guest to do this, specifically if we
> switch from INTx to MSI mode.
>
> Signed-off-by: Jan Kiszka<jan.kiszka@siemens.com>
> ---
> virt/kvm/assigned-dev.c | 3 +++
> 1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/virt/kvm/assigned-dev.c b/virt/kvm/assigned-dev.c
> index 7c98928..ecc4419 100644
> --- a/virt/kvm/assigned-dev.c
> +++ b/virt/kvm/assigned-dev.c
> @@ -141,6 +141,9 @@ static void deassign_guest_irq(struct kvm *kvm,
> kvm_unregister_irq_ack_notifier(kvm,&assigned_dev->ack_notifier);
> assigned_dev->ack_notifier.gsi = -1;
>
> + kvm_set_irq(assigned_dev->kvm, assigned_dev->irq_source_id,
> + assigned_dev->guest_irq, 0);
> +
> if (assigned_dev->irq_source_id != -1)
> kvm_free_irq_source_id(kvm, assigned_dev->irq_source_id);
> assigned_dev->irq_source_id = -1;

I guess this can't hurt. Did you see it happen in practice?

Note: all this kvm_set_irq(..., [01]) is incorrect as it doesn't account
for polarity. Currently the qemu-emulated chipset uses level high pci
interrupts, but that's not a given from kvm's point of view.

I think vfio fixes this by only routing msi interrupts via the kernel,
and routing level interrupts through userspace, which can adjust
polarity. Alex/Michael?

--
error compiling committee.c: too many arguments to function