Hi Jean,
On 11/23/21 4:53 PM, Jean-Philippe Brucker wrote:
> Support identity domains for devices that do not offer the
> VIRTIO_IOMMU_F_BYPASS_CONFIG feature, by creating 1:1 mappings between
> the virtual and physical address space. Identity domains created this
> way still perform noticeably better than DMA domains, because they don't
> have the overhead of setting up and tearing down mappings at runtime.
> The performance difference between this and bypass is minimal in
> comparison.
>
> It does not matter that the physical addresses in the identity mappings
> do not all correspond to memory. By enabling passthrough we are trusting
> the device driver and the device itself to only perform DMA to suitable
> locations. In some cases it may even be desirable to perform DMA to MMIO
> regions.
>
> Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> ---
> drivers/iommu/virtio-iommu.c | 63 +++++++++++++++++++++++++++++++++---
> 1 file changed, 58 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
> index eceb9281c8c1..6a8a52b4297b 100644
> --- a/drivers/iommu/virtio-iommu.c
> +++ b/drivers/iommu/virtio-iommu.c
> @@ -375,6 +375,55 @@ static size_t viommu_del_mappings(struct viommu_domain *vdomain,
> return unmapped;
> }
>
> +/*
> + * Fill the domain with identity mappings, skipping the device's reserved
> + * regions.
> + */
> +static int viommu_domain_map_identity(struct viommu_endpoint *vdev,
> + struct viommu_domain *vdomain)
> +{
> + int ret;
> + struct iommu_resv_region *resv;
> + u64 iova = vdomain->domain.geometry.aperture_start;
> + u64 limit = vdomain->domain.geometry.aperture_end;
> + u32 flags = VIRTIO_IOMMU_MAP_F_READ | VIRTIO_IOMMU_MAP_F_WRITE;
> + unsigned long granule = 1UL << __ffs(vdomain->domain.pgsize_bitmap);
> +
> + iova = ALIGN(iova, granule);
> + limit = ALIGN_DOWN(limit + 1, granule) - 1;
> +
> + list_for_each_entry(resv, &vdev->resv_regions, list) {
> + u64 resv_start = ALIGN_DOWN(resv->start, granule);
> + u64 resv_end = ALIGN(resv->start + resv->length, granule) - 1;
> +
> + if (resv_end < iova || resv_start > limit)
> + /* No overlap */
> + continue;
> +
> + if (resv_start > iova) {
> + ret = viommu_add_mapping(vdomain, iova, resv_start - 1,
> + (phys_addr_t)iova, flags);
> + if (ret)
> + goto err_unmap;
> + }
> +
> + if (resv_end >= limit)
> + return 0;
> +
> + iova = resv_end + 1;
> + }
> +
> + ret = viommu_add_mapping(vdomain, iova, limit, (phys_addr_t)iova,
> + flags);
> + if (ret)
> + goto err_unmap;
> + return 0;
> +
> +err_unmap:
> + viommu_del_mappings(vdomain, 0, iova);
> + return ret;
> +}
> +
> /*
> * viommu_replay_mappings - re-send MAP requests
> *
> @@ -637,14 +686,18 @@ static int viommu_domain_finalise(struct viommu_endpoint *vdev,
> vdomain->viommu = viommu;
>
> if (domain->type == IOMMU_DOMAIN_IDENTITY) {
> - if (!virtio_has_feature(viommu->vdev,
> - VIRTIO_IOMMU_F_BYPASS_CONFIG)) {
> + if (virtio_has_feature(viommu->vdev,
> + VIRTIO_IOMMU_F_BYPASS_CONFIG)) {
> + vdomain->bypass = true;
> + return 0;
> + }
> +
> + ret = viommu_domain_map_identity(vdev, vdomain);
> + if (ret) {
> ida_free(&viommu->domain_ids, vdomain->id);
> - vdomain->viommu = 0;
> + vdomain->viommu = NULL;
nit: that change could have been done in patch 2
> return -EOPNOTSUPP;
> }
> -
> - vdomain->bypass = true;
> }
>
> return 0;
Besides
Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx>
Eric
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