netdev - Re: Re: [PATCH v6 08/10] vduse: Implement an MMU-based IOMMU driver

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Date:   Thu, 8 Apr 2021 13:27:27 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Parav Pandit <parav@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Christian Brauner <christian.brauner@...onical.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Matthew Wilcox <willy@...radead.org>, viro@...iv.linux.org.uk,
        Jens Axboe <axboe@...nel.dk>, bcrl@...ck.org,
        Jonathan Corbet <corbet@....net>,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
        kvm@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: Re: [PATCH v6 08/10] vduse: Implement an MMU-based IOMMU driver

On Thu, Apr 8, 2021 at 11:26 AM Jason Wang <jasowang@...hat.com> wrote:
>
>
> 在 2021/3/31 下午4:05, Xie Yongji 写道:
> > 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@...edance.com>
>
>
> Acked-by: Jason Wang <jasowang@...hat.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?".
>

OK.

>
> > +{
> > +     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?
>

Fine.

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

Agree.

Thanks,
Yongji