Re: [PATCH V2] vhost: correctly turn on VIRTIO_F_IOMMU_PLATFORM

[Halil Pasic]

On Wed, 26 Feb 2020 08:37:13 -0500
"Michael S. Tsirkin" <address@hidden> wrote:

> On Wed, Feb 26, 2020 at 02:28:39PM +0100, Halil Pasic wrote:
> > On Wed, 26 Feb 2020 17:43:57 +0800
> > Jason Wang <address@hidden> wrote:
> > 
> > > We turn on device IOTLB via VIRTIO_F_IOMMU_PLATFORM unconditionally on
> > > platform without IOMMU support. This can lead unnecessary IOTLB
> > > transactions which will damage the performance.
> > > 
> > > Fixing this by check whether the device is backed by IOMMU and disable
> > > device IOTLB.
> > > 
> > > Reported-by: Halil Pasic <address@hidden>
> > > Fixes: c471ad0e9bd46 ("vhost_net: device IOTLB support")
> > > Cc: address@hidden
> > > Signed-off-by: Jason Wang <address@hidden>
> > 
> > Tested-by: Halil Pasic <address@hidden>
> > Reviewed-by: Halil Pasic <address@hidden>
> > 
> > Thank you very much for fixing this! BTW as I mentioned before it
> > fixes vhost-vsock with iommu_platform=on as well.
> 
> Fixes as in improves performance?

No, fixes like one does not get something like:
qemu-system-s390x: vhost_set_features failed: Operation not supported (95)
qemu-system-s390x: Error starting vhost: 95
any more.

Regards,
Halil

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