> On Mon, Jul 22, 2024 at 03:22:22PM +0800, Jason Wang wrote: > > On Fri, Jul 19, 2024 at 11:40 PM Srujana Challa <schalla@xxxxxxxxxxx> > wrote: > > > > > > > On Thu, May 30, 2024 at 03:48:23PM +0530, Srujana Challa wrote: > > > > > This commit introduces support for an UNSAFE, no-IOMMU mode in > > > > > the vhost-vdpa driver. When enabled, this mode provides no > > > > > device isolation, no DMA translation, no host kernel protection, > > > > > and cannot be used for device assignment to virtual machines. It > > > > > requires RAWIO permissions and will taint the kernel. > > > > > This mode requires enabling the > > > > "enable_vhost_vdpa_unsafe_noiommu_mode" > > > > > option on the vhost-vdpa driver. This mode would be useful to > > > > > get better performance on specifice low end machines and can be > > > > > leveraged by embedded platforms where applications run in controlled > environment. > > > > > > > > > > Signed-off-by: Srujana Challa <schalla@xxxxxxxxxxx> > > > > > > > > Thought hard about that. > > > > I think given vfio supports this, we can do that too, and the extension is > small. > > > > > > > > However, it looks like setting this parameter will automatically > > > > change the behaviour for existing userspace when > IOMMU_DOMAIN_IDENTITY is set. Our initial thought was to support only for no-iommu case, in which domain itself won't be exist. So, we can modify the code as below to check for only presence of domain. I think, only handling of no-iommu case wouldn't effect the existing userspace. + if ((!domain) && vhost_vdpa_noiommu && capable(CAP_SYS_RAWIO)) { > > > > > > > > I suggest a new domain type for use just for this purpose. > > > > I'm not sure I get this, we want to bypass IOMMU, so it doesn't even > > have a doman. > > yes, a fake one. or come up with some other flag that userspace will set. > > > > This way if host has > > > > an iommu, then the same kernel can run both VMs with isolation and > > > > unsafe embedded apps without. > > > Could you provide further details on this concept? What criteria > > > would determine the configuration of the new domain type? Would this > > > require a boot parameter similar to IOMMU_DOMAIN_IDENTITY, such as > iommu.passthrough=1 or iommu.pt? > > > > Thanks > > > > > > > > > > > --- > > > > > drivers/vhost/vdpa.c | 23 +++++++++++++++++++++++ > > > > > 1 file changed, 23 insertions(+) > > > > > > > > > > diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c index > > > > > bc4a51e4638b..d071c30125aa 100644 > > > > > --- a/drivers/vhost/vdpa.c > > > > > +++ b/drivers/vhost/vdpa.c > > > > > @@ -36,6 +36,11 @@ enum { > > > > > > > > > > #define VHOST_VDPA_IOTLB_BUCKETS 16 > > > > > > > > > > +bool vhost_vdpa_noiommu; > > > > > +module_param_named(enable_vhost_vdpa_unsafe_noiommu_mode, > > > > > + vhost_vdpa_noiommu, bool, 0644); > > > > > +MODULE_PARM_DESC(enable_vhost_vdpa_unsafe_noiommu_mode, > > > > "Enable > > > > > +UNSAFE, no-IOMMU mode. This mode provides no device isolation, > > > > > +no DMA translation, no host kernel protection, cannot be used > > > > > +for device assignment to virtual machines, requires RAWIO > > > > > +permissions, and will taint the kernel. If you do not know what this is > for, step away. > > > > > +(default: false)"); > > > > > + > > > > > struct vhost_vdpa_as { > > > > > struct hlist_node hash_link; > > > > > struct vhost_iotlb iotlb; > > > > > @@ -60,6 +65,7 @@ struct vhost_vdpa { > > > > > struct vdpa_iova_range range; > > > > > u32 batch_asid; > > > > > bool suspended; > > > > > + bool noiommu_en; > > > > > }; > > > > > > > > > > static DEFINE_IDA(vhost_vdpa_ida); @@ -887,6 +893,10 @@ static > > > > > void vhost_vdpa_general_unmap(struct vhost_vdpa *v, { > > > > > struct vdpa_device *vdpa = v->vdpa; > > > > > const struct vdpa_config_ops *ops = vdpa->config; > > > > > + > > > > > + if (v->noiommu_en) > > > > > + return; > > > > > + > > > > > if (ops->dma_map) { > > > > > ops->dma_unmap(vdpa, asid, map->start, map->size); > > > > > } else if (ops->set_map == NULL) { @@ -980,6 +990,9 @@ > > > > > static int vhost_vdpa_map(struct vhost_vdpa *v, > > > > struct vhost_iotlb *iotlb, > > > > > if (r) > > > > > return r; > > > > > > > > > > + if (v->noiommu_en) > > > > > + goto skip_map; > > > > > + > > > > > if (ops->dma_map) { > > > > > r = ops->dma_map(vdpa, asid, iova, size, pa, perm, opaque); > > > > > } else if (ops->set_map) { > > > > > @@ -995,6 +1008,7 @@ static int vhost_vdpa_map(struct vhost_vdpa > > > > > *v, > > > > struct vhost_iotlb *iotlb, > > > > > return r; > > > > > } > > > > > > > > > > +skip_map: > > > > > if (!vdpa->use_va) > > > > > atomic64_add(PFN_DOWN(size), &dev->mm->pinned_vm); > > > > > > > > > > @@ -1298,6 +1312,7 @@ static int vhost_vdpa_alloc_domain(struct > > > > vhost_vdpa *v) > > > > > struct vdpa_device *vdpa = v->vdpa; > > > > > const struct vdpa_config_ops *ops = vdpa->config; > > > > > struct device *dma_dev = vdpa_get_dma_dev(vdpa); > > > > > + struct iommu_domain *domain; > > > > > const struct bus_type *bus; > > > > > int ret; > > > > > > > > > > @@ -1305,6 +1320,14 @@ static int vhost_vdpa_alloc_domain(struct > > > > vhost_vdpa *v) > > > > > if (ops->set_map || ops->dma_map) > > > > > return 0; > > > > > > > > > > + domain = iommu_get_domain_for_dev(dma_dev); > > > > > + if ((!domain || domain->type == IOMMU_DOMAIN_IDENTITY) && > > > > > + vhost_vdpa_noiommu && capable(CAP_SYS_RAWIO)) { > > > > > > > > So if userspace does not have CAP_SYS_RAWIO instead of failing > > > > with a permission error the functionality changes silently? > > > > That's confusing, I think. > > > Yes, you are correct. I will modify the code to return error when > > > vhost_vdpa_noiommu is set and CAP_SYS_RAWIO is not set. > > > > > > Thanks. > > > > > > > > > > > > > + add_taint(TAINT_USER, LOCKDEP_STILL_OK); > > > > > + dev_warn(&v->dev, "Adding kernel taint for noiommu > > > > > + on > > > > device\n"); > > > > > + v->noiommu_en = true; > > > > > + return 0; > > > > > + } > > > > > bus = dma_dev->bus; > > > > > if (!bus) > > > > > return -EFAULT; > > > > > -- > > > > > 2.25.1 > > >