On Thu, 29 Oct 2015 18:09:47 -0700
Andy Lutomirski <luto@xxxxxxxxxx> wrote:
> virtio_ring currently sends the device (usually a hypervisor)
> physical addresses of its I/O buffers. This is okay when DMA
> addresses and physical addresses are the same thing, but this isn't
> always the case. For example, this never works on Xen guests, and
> it is likely to fail if a physical "virtio" device ever ends up
> behind an IOMMU or swiotlb.
>
> The immediate use case for me is to enable virtio on Xen guests.
> For that to work, we need vring to support DMA address translation
> as well as a corresponding change to virtio_pci or to another
> driver.
>
> With this patch, if enabled, virtfs survives kmemleak and
> CONFIG_DMA_API_DEBUG.
>
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
> ---
> drivers/virtio/Kconfig | 2 +-
> drivers/virtio/virtio_ring.c | 190 +++++++++++++++++++++++++++++++--------
> tools/virtio/linux/dma-mapping.h | 17 ++++
> 3 files changed, 172 insertions(+), 37 deletions(-)
> create mode 100644 tools/virtio/linux/dma-mapping.h
> static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
> {
> - unsigned int i;
> + unsigned int i, j;
> + u16 nextflag = cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT);
>
> /* Clear data ptr. */
> - vq->data[head] = NULL;
> + vq->desc_state[head].data = NULL;
>
> - /* Put back on free list: find end */
> + /* Put back on free list: unmap first-level descriptors and find end */
> i = head;
>
> - /* Free the indirect table */
> - if (vq->vring.desc[i].flags & cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_INDIRECT))
> - kfree(phys_to_virt(virtio64_to_cpu(vq->vq.vdev, vq->vring.desc[i].addr)));
> -
> - while (vq->vring.desc[i].flags & cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_NEXT)) {
> + while (vq->vring.desc[i].flags & nextflag) {
> + vring_unmap_one(vq, &vq->vring.desc[i]);
> i = virtio16_to_cpu(vq->vq.vdev, vq->vring.desc[i].next);
> vq->vq.num_free++;
> }
>
> + vring_unmap_one(vq, &vq->vring.desc[i]);
> vq->vring.desc[i].next = cpu_to_virtio16(vq->vq.vdev, vq->free_head);
> vq->free_head = head;
> +
> /* Plus final descriptor */
> vq->vq.num_free++;
> +
> + /* Free the indirect table, if any, now that it's unmapped. */
> + if (vq->desc_state[head].indir_desc) {
> + struct vring_desc *indir_desc = vq->desc_state[head].indir_desc;
> + u32 len = vq->vring.desc[head].len;
This one needs to be virtio32_to_cpu(...) as well.
> +
> + BUG_ON(!(vq->vring.desc[head].flags &
> + cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_INDIRECT)));
> + BUG_ON(len == 0 || len % sizeof(struct vring_desc));
> +
> + for (j = 0; j < len / sizeof(struct vring_desc); j++)
> + vring_unmap_one(vq, &indir_desc[j]);
> +
> + kfree(vq->desc_state[head].indir_desc);
> + vq->desc_state[head].indir_desc = NULL;
> + }
> }
With that change on top of your current branch, I can boot (root on
virtio-blk, either virtio-1 or legacy virtio) on current qemu master
with kvm enabled on s390. Haven't tried anything further.
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