From: "Michael S. Tsirkin" <mst@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Shannon Zhao <zhaoshenglong@huawei.com>,
qemu-devel@nongnu.org, qemu-arm@nongnu.org,
peter.maydell@linaro.org, christoffer.dall@linaro.org
Subject: Re: [Qemu-devel] [PATCH V2] virtio: Fix no interrupt when not creating msi controller
Date: Tue, 24 Jan 2017 16:44:02 +0200 [thread overview]
Message-ID: <20170124164204-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <5760ee8c-f567-0dfd-456f-65f8957b22e2@redhat.com>
On Tue, Jan 24, 2017 at 10:25:00AM +0100, Paolo Bonzini wrote:
>
>
> On 23/01/2017 18:04, Michael S. Tsirkin wrote:
> >> For virtio-blk, my patch moved the setting of ISR from
> >> virtio_queue_guest_notifier_read to virtio_notify_irqfd. This is
> >> because the irqfd emulation only needs to trigger the interrupt.
> >> Setting the ISR should have been done elsewhere.
> >>
> >> Can vhost set ISR (I thought it couldn't)? If so, it seems like ARM was
> >> relying on QEMU's irqfd emulation, as a work around for vhost not
> >> setting ISR. But this only works if irqfd is directed to QEMU and not
> >> to KVM. So if vhost cannot set ISR, I think vhost should be disabled
> >> unless MSI is active.
> >>
> >> Am I missing something?
> >
> > vhost doesn't set ISR ATM. Without MSI we are always bouncing
> > interrupts through QEMU in particular in order to set ISR.
>
> Where is the code that disables KVM irqfd?
>
> Paolo
This bit in virtio_pci_set_guest_notifiers does the trick I think:
bool with_irqfd = msix_enabled(&proxy->pci_dev) &&
kvm_msi_via_irqfd_enabled();
I don't think we ever used irqfd for level interrupts.
> > Disabling vhost when user requested it was what we did
> > at some point but this just confused people.
> >
> >
next prev parent reply other threads:[~2017-01-24 14:44 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-23 0:55 [Qemu-devel] [PATCH V2] virtio: Fix no interrupt when not creating msi controller Shannon Zhao
2017-01-23 16:07 ` Michael S. Tsirkin
2017-01-23 16:46 ` Paolo Bonzini
2017-01-23 17:04 ` Michael S. Tsirkin
2017-01-24 9:25 ` Paolo Bonzini
2017-01-24 14:44 ` Michael S. Tsirkin [this message]
2017-01-24 15:00 ` Paolo Bonzini
2017-01-24 15:05 ` Michael S. Tsirkin
2017-01-24 15:50 ` Paolo Bonzini
2017-01-24 15:55 ` Michael S. Tsirkin
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