Re: [Qemu-devel] [PATCH 3/3] virtio: set ISR on dataplane notifications

[Paolo Bonzini]

On 15/11/2016 16:44, Michael S. Tsirkin wrote:
> True. We could drop it from non-data plane, it's just that we never had
> a reason to. vhost in kernel does not set ISR in MSI mode, either.

Yeah, I suspected that.  But dropping it from non-dataplane would break
Windows hibernation and crashdump, just like it did for Alex.

> What we have in spec is:
> 
> The device MUST set the Device Configuration Interrupt bit in ISR status
> before sending a device configu-
> ration change notification to the driver.
> If MSI-X capability is disabled, the device MUST set the Queue Interrupt
> bit in ISR status before sending a
> virtqueue notification to the driver.
> If MSI-X capability is disabled, the device MUST set the Interrupt
> Status bit in the PCI Status register in the
> PCI Configuration Header of the device to the logical OR of all bits in
> ISR status of the device. The device
> then asserts/deasserts INT#x interrupts unless masked according to
> standard PCI rules [PCI].
> The device MUST reset ISR status to 0 on driver read.
> 
> 
> 
> 
> If MSI-X capability is enabled, the driver SHOULD NOT access ISR status
> upon detecting a Queue Interrupt.
> 
> 
> 
> It can be clearer, but IMHO it's reasonably clear that devices
> do not have to set this bit in MSI mode.

Yes, it is.  We can just document it in the release notes, but then the
fix is not particularly intrusive.

Paolo