Subject: Re: [PATCH v3] vhost/vdpa: Add MSI translation tables to iommu for software-managed MSI

From: "Michael S. Tsirkin" <[email-masked]>
Date: Fri, 29 Mar 2024 05:13:27 -0400

On Wed, Mar 27, 2024 at 05:08:57PM +0800, Jason Wang wrote:
> On Thu, Mar 21, 2024 at 3:00 PM Michael S. Tsirkin <[email-masked]> wrote:
> >
> > On Wed, Mar 20, 2024 at 06:19:12PM +0800, Wang Rong wrote:
> > > From: Rong Wang <[email-masked]>
> > >
> > > Once enable iommu domain for one device, the MSI
> > > translation tables have to be there for software-managed MSI.
> > > Otherwise, platform with software-managed MSI without an
> > > irq bypass function, can not get a correct memory write event
> > > from pcie, will not get irqs.
> > > The solution is to obtain the MSI phy base address from
> > > iommu reserved region, and set it to iommu MSI cookie,
> > > then translation tables will be created while request irq.
> > >
> > > Change log
> > > ----------
> > >
> > > v1->v2:
> > > - add resv iotlb to avoid overlap mapping.
> > > v2->v3:
> > > - there is no need to export the iommu symbol anymore.
> > >
> > > Signed-off-by: Rong Wang <[email-masked]>
> >
> > There's in interest to keep extending vhost iotlb -
> > we should just switch over to iommufd which supports
> > this already.
> 
> IOMMUFD is good but VFIO supports this before IOMMUFD.

You mean VFIO migrated to IOMMUFD but of course they keep supporting
their old UAPI? OK and point being?

> This patch
> makes vDPA run without a backporting of full IOMMUFD in the production
> environment. I think it's worth.

Where do we stop? saying no to features is the only tool maintainers
have to make cleanups happen, otherwise people will just keep piling
stuff up.

> If you worry about the extension, we can just use the vhost iotlb
> existing facility to do this.
> 
> Thanks
> 
> >
> > > ---
> > >  drivers/vhost/vdpa.c | 59 +++++++++++++++++++++++++++++++++++++++++---
> > >  1 file changed, 56 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> > > index ba52d128aeb7..28b56b10372b 100644
> > > --- a/drivers/vhost/vdpa.c
> > > +++ b/drivers/vhost/vdpa.c
> > > @@ -49,6 +49,7 @@ struct vhost_vdpa {
> > >       struct completion completion;
> > >       struct vdpa_device *vdpa;
> > >       struct hlist_head as[VHOST_VDPA_IOTLB_BUCKETS];
> > > +     struct vhost_iotlb resv_iotlb;
> > >       struct device dev;
> > >       struct cdev cdev;
> > >       atomic_t opened;
> > > @@ -247,6 +248,7 @@ static int _compat_vdpa_reset(struct vhost_vdpa *v)
> > >  static int vhost_vdpa_reset(struct vhost_vdpa *v)
> > >  {
> > >       v->in_batch = 0;
> > > +     vhost_iotlb_reset(&v->resv_iotlb);
> > >       return _compat_vdpa_reset(v);
> > >  }
> > >
> > > @@ -1219,10 +1221,15 @@ static int vhost_vdpa_process_iotlb_update(struct vhost_vdpa *v,
> > >           msg->iova + msg->size - 1 > v->range.last)
> > >               return -EINVAL;
> > >
> > > +     if (vhost_iotlb_itree_first(&v->resv_iotlb, msg->iova,
> > > +                                     msg->iova + msg->size - 1))
> > > +             return -EINVAL;
> > > +
> > >       if (vhost_iotlb_itree_first(iotlb, msg->iova,
> > >                                   msg->iova + msg->size - 1))
> > >               return -EEXIST;
> > >
> > > +
> > >       if (vdpa->use_va)
> > >               return vhost_vdpa_va_map(v, iotlb, msg->iova, msg->size,
> > >                                        msg->uaddr, msg->perm);
> > > @@ -1307,6 +1314,45 @@ static ssize_t vhost_vdpa_chr_write_iter(struct kiocb *iocb,
> > >       return vhost_chr_write_iter(dev, from);
> > >  }
> > >
> > > +static int vhost_vdpa_resv_iommu_region(struct iommu_domain *domain, struct device *dma_dev,
> > > +     struct vhost_iotlb *resv_iotlb)
> > > +{
> > > +     struct list_head dev_resv_regions;
> > > +     phys_addr_t resv_msi_base = 0;
> > > +     struct iommu_resv_region *region;
> > > +     int ret = 0;
> > > +     bool with_sw_msi = false;
> > > +     bool with_hw_msi = false;
> > > +
> > > +     INIT_LIST_HEAD(&dev_resv_regions);
> > > +     iommu_get_resv_regions(dma_dev, &dev_resv_regions);
> > > +
> > > +     list_for_each_entry(region, &dev_resv_regions, list) {
> > > +             ret = vhost_iotlb_add_range_ctx(resv_iotlb, region->start,
> > > +                             region->start + region->length - 1,
> > > +                             0, 0, NULL);
> > > +             if (ret) {
> > > +                     vhost_iotlb_reset(resv_iotlb);
> > > +                     break;
> > > +             }
> > > +
> > > +             if (region->type == IOMMU_RESV_MSI)
> > > +                     with_hw_msi = true;
> > > +
> > > +             if (region->type == IOMMU_RESV_SW_MSI) {
> > > +                     resv_msi_base = region->start;
> > > +                     with_sw_msi = true;
> > > +             }
> > > +     }
> > > +
> > > +     if (!ret && !with_hw_msi && with_sw_msi)
> > > +             ret = iommu_get_msi_cookie(domain, resv_msi_base);
> > > +
> > > +     iommu_put_resv_regions(dma_dev, &dev_resv_regions);
> > > +
> > > +     return ret;
> > > +}
> > > +
> > >  static int vhost_vdpa_alloc_domain(struct vhost_vdpa *v)
> > >  {
> > >       struct vdpa_device *vdpa = v->vdpa;
> > > @@ -1335,11 +1381,16 @@ static int vhost_vdpa_alloc_domain(struct vhost_vdpa *v)
> > >
> > >       ret = iommu_attach_device(v->domain, dma_dev);
> > >       if (ret)
> > > -             goto err_attach;
> > > +             goto err_alloc_domain;
> > >
> > > -     return 0;
> > > +     ret = vhost_vdpa_resv_iommu_region(v->domain, dma_dev, &v->resv_iotlb);
> > > +     if (ret)
> > > +             goto err_attach_device;
> > >
> > > -err_attach:
> > > +     return 0;
> > > +err_attach_device:
> > > +     iommu_detach_device(v->domain, dma_dev);
> > > +err_alloc_domain:
> > >       iommu_domain_free(v->domain);
> > >       v->domain = NULL;
> > >       return ret;
> > > @@ -1595,6 +1646,8 @@ static int vhost_vdpa_probe(struct vdpa_device *vdpa)
> > >               goto err;
> > >       }
> > >
> > > +     vhost_iotlb_init(&v->resv_iotlb, 0, 0);
> > > +
> > >       r = dev_set_name(&v->dev, "vhost-vdpa-%u", minor);
> > >       if (r)
> > >               goto err;
> > > --
> > > 2.27.0
> > >
> >