Virtualization - Apr 2021 - [PATCH v6 08/10] vduse: Implement an MMU-based IOMMU driver

? 2021/3/31 ??4:05, Xie Yongji ??:
> This implements an MMU-based IOMMU driver to support mapping
> kernel dma buffer into userspace. The basic idea behind it is
> treating MMU (VA->PA) as IOMMU (IOVA->PA). The driver will set
> up MMU mapping instead of IOMMU mapping for the DMA transfer so
> that the userspace process is able to use its virtual address to
> access the dma buffer in kernel.
>
> And to avoid security issue, a bounce-buffering mechanism is
> introduced to prevent userspace accessing the original buffer
> directly.
>
> Signed-off-by: Xie Yongji <xieyongji at bytedance.com>

Acked-by: Jason Wang <jasowang at redhat.com>

With some nits:

> ---
>   drivers/vdpa/vdpa_user/iova_domain.c | 521
+++++++++++++++++++++++++++++++++++
>   drivers/vdpa/vdpa_user/iova_domain.h |  70 +++++
>   2 files changed, 591 insertions(+)
>   create mode 100644 drivers/vdpa/vdpa_user/iova_domain.c
>   create mode 100644 drivers/vdpa/vdpa_user/iova_domain.h

[...]

> +static void vduse_domain_bounce(struct vduse_iova_domain *domain,
> +				dma_addr_t iova, size_t size,
> +				enum dma_data_direction dir)
> +{
> +	struct vduse_bounce_map *map;
> +	unsigned int offset;
> +	void *addr;
> +	size_t sz;
> +
> +	while (size) {
> +		map = &domain->bounce_maps[iova >> PAGE_SHIFT];
> +		offset = offset_in_page(iova);
> +		sz = min_t(size_t, PAGE_SIZE - offset, size);
> +
> +		if (WARN_ON(!map->bounce_page ||
> +			    map->orig_phys == INVALID_PHYS_ADDR))
> +			return;
> +
> +		addr = page_address(map->bounce_page) + offset;
> +		do_bounce(map->orig_phys + offset, addr, sz, dir);
> +		size -= sz;
> +		iova += sz;
> +	}
> +}
> +
> +static struct page *
> +vduse_domain_get_mapping_page(struct vduse_iova_domain *domain, u64 iova)

It's better to rename this as "vduse_domain_get_coherent_page?".

> +{
> +	u64 start = iova & PAGE_MASK;
> +	u64 last = start + PAGE_SIZE - 1;
> +	struct vhost_iotlb_map *map;
> +	struct page *page = NULL;
> +
> +	spin_lock(&domain->iotlb_lock);
> +	map = vhost_iotlb_itree_first(domain->iotlb, start, last);
> +	if (!map)
> +		goto out;
> +
> +	page = pfn_to_page((map->addr + iova - map->start) >>
PAGE_SHIFT);
> +	get_page(page);
> +out:
> +	spin_unlock(&domain->iotlb_lock);
> +
> +	return page;
> +}
> +

[...]

> +
> +static dma_addr_t
> +vduse_domain_alloc_iova(struct iova_domain *iovad,
> +			unsigned long size, unsigned long limit)
> +{
> +	unsigned long shift = iova_shift(iovad);
> +	unsigned long iova_len = iova_align(iovad, size) >> shift;
> +	unsigned long iova_pfn;
> +
> +	if (iova_len < (1 << (IOVA_RANGE_CACHE_MAX_SIZE - 1)))
> +		iova_len = roundup_pow_of_two(iova_len);

Let's add a comment as what has been done in dma-iommu.c?

(In the future, it looks to me it's better to move them to 
alloc_iova_fast()).

Thanks