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Re: [Qemu-devel] [PATCH V2] virtio: Fix no interrupt when not creating m

From: Paolo Bonzini
Subject: Re: [Qemu-devel] [PATCH V2] virtio: Fix no interrupt when not creating msi controller
Date: Tue, 24 Jan 2017 10:25:00 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1

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?


> Disabling vhost when user requested it was what we did
> at some point but this just confused people.

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