On Thu, May 30, 2024 at 6:18 PM Srujana Challa <scha...@marvell.com> 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.
I wonder if it's better to do it per driver:
1) we have device that use its own IOMMU, one example is the mlx5 vDPA device
2) we have software devices which doesn't require IOMMU at all (but
still with protection)
Thanks
>
> Signed-off-by: Srujana Challa <scha...@marvell.com>
> ---
> 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)) {
> + 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
>
