Re: [PULL v4 15/47] intel_iommu: support snoop control

[Jason Wang]

On Thu, Mar 31, 2022 at 5:51 PM Peter Maydell <peter.maydell@linaro.org> wrote:
>
> On Mon, 7 Mar 2022 at 22:45, Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > From: Jason Wang <jasowang@redhat.com>
> >
> > SC is required for some kernel features like vhost-vDPA. So this patch
> > implements basic SC feature. The idea is pretty simple, for software
> > emulated DMA it would be always coherent. In this case we can simple
> > advertise ECAP_SC bit. For VFIO and vhost, thing will be more much
> > complicated, so this patch simply fail the IOMMU notifier
> > registration.
> >
> > In the future, we may want to have a dedicated notifiers flag or
> > similar mechanism to demonstrate the coherency so VFIO could advertise
> > that if it has VFIO_DMA_CC_IOMMU, for vhost kernel backend we don't
> > need that since it's a software backend.
>
> Hi; Coverity points out (CID 1487174) an error in this change:
>
> > --- a/hw/i386/intel_iommu.c
> > +++ b/hw/i386/intel_iommu.c
> > @@ -3030,6 +3030,13 @@ static int 
> > vtd_iommu_notify_flag_changed(IOMMUMemoryRegion *iommu,
> >      VTDAddressSpace *vtd_as = container_of(iommu, VTDAddressSpace, iommu);
> >      IntelIOMMUState *s = vtd_as->iommu_state;
> >
> > +    /* TODO: add support for VFIO and vhost users */
> > +    if (s->snoop_control) {
> > +        error_setg_errno(errp, -ENOTSUP,
> > +                         "Snoop Control with vhost or VFIO is not 
> > supported");
> > +        return -ENOTSUP;
> > +    }
>
> error_setg_errno() expects a normal errno value, not a negated
> one, so we should be passing it "ENOTSUP" here, not "-ENOTSUP".

Will post a fix soon.

Thanks

>
> thanks
> -- PMM
>