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SubjectRe: [PATCH v7 0/9] virtio DMA API, yet again
On Tue, 2 Feb 2016, Andy Lutomirski wrote:
> This switches virtio to use the DMA API on Xen and if requested by
> module option.
>
> This fixes virtio on Xen, and it should break anything because it's
> off by default on everything except Xen PV on x86.
>
> To the Xen people: is this okay? If it doesn't work on other Xen
> variants (PVH? HVM?), can you submit follow-up patches to fix it?

I have been waiting for something like this for a long time: up to now
it wasn't possible to use Xen inside a VM with virtio devices.

You can add my:

Tested-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>


> To everyone else: we've waffled on this for way too long. I think
> we should to get DMA API implementation in with a conservative
> policy like this rather than waiting until we achieve perfection.
> I'm tired of carrying these patches around.
>
> I changed queue allocation around a bit in this version. Per Michael's
> request, we no longer use dma_zalloc_coherent in the !dma_api case.
> Instead we use alloc_pages_exact, just like the current code does.
> This simplifies the ring address accessors, because they can always
> load from the dma addr rather than depending on vring_use_dma_api
> themselves.
>
> There's an odd warning in here if the ring's physical address
> doesn't fit in a dma_addr_t. This could only possible happen on
> really weird configurations in which phys_addr_t is wider than
> dma_addr_t. AFAICT this is only possible on i386 PAE systems and on
> MIPS, and even there it only happens if highmem is off. But that
> means we're safe, since we should never end up with high allocations
> on non-highmem systems unless we explicitly ask for them, which we
> don't.
>
> If this is too scary, I can add yet more cruft to avoid it, but
> it seems harmless enough to me, and it means that the driver will
> be totally clean once all the vring_use_dma_api calls go away.
>
> Michael, if these survive review, can you stage these in your tree?
> Can you also take a look at tools/virtio? I probably broke it, but I
> couldn't get it to build without these patches either, so I'm stuck.
>
> Changes from v6:
> - Remove HAVE_DMA_ATTRS and add Acked-by (Cornelia)
> - Add some missing signed-off-by lines from me (whoops)
> - Rework queue allocation (Michael)
>
> Changes from v5:
> - Typo fixes (David Woodhouse)
> - Use xen_domain() to detect Xen (David Vrabel)
> - Pass struct vring_virtqueue * into vring_use_dma_api for future proofing
> - Removed module parameter (Michael)
>
> Changes from v4:
> - Bake vring_use_dma_api in from the beginning.
> - Automatically enable only on Xen.
> - Add module parameter.
> - Add s390 and alpha DMA API implementations.
> - Rebase to 4.5-rc1.
>
> Changes from v3:
> - More big-endian fixes.
> - Added better virtio-ring APIs that handle allocation and use them in
> virtio-mmio and virtio-pci.
> - Switch to Michael's virtio-net patch.
>
> Changes from v2:
> - Fix vring_mapping_error incorrect argument
>
> Changes from v1:
> - Fix an endian conversion error causing a BUG to hit.
> - Fix a DMA ordering issue (swiotlb=force works now).
> - Minor cleanups.
>
> Andy Lutomirski (6):
> vring: Introduce vring_use_dma_api()
> virtio_ring: Support DMA APIs
> virtio: Add improved queue allocation API
> virtio_mmio: Use the DMA API if enabled
> virtio_pci: Use the DMA API if enabled
> vring: Use the DMA API on Xen
>
> Christian Borntraeger (3):
> dma: Provide simple noop dma ops
> alpha/dma: use common noop dma ops
> s390/dma: Allow per device dma ops
>
> arch/alpha/kernel/pci-noop.c | 46 +---
> arch/s390/Kconfig | 5 +-
> arch/s390/include/asm/device.h | 6 +-
> arch/s390/include/asm/dma-mapping.h | 6 +-
> arch/s390/pci/pci.c | 1 +
> arch/s390/pci/pci_dma.c | 4 +-
> drivers/virtio/Kconfig | 2 +-
> drivers/virtio/virtio_mmio.c | 67 ++----
> drivers/virtio/virtio_pci_common.h | 6 -
> drivers/virtio/virtio_pci_legacy.c | 42 ++--
> drivers/virtio/virtio_pci_modern.c | 61 ++---
> drivers/virtio/virtio_ring.c | 439 +++++++++++++++++++++++++++++++-----
> include/linux/dma-mapping.h | 2 +
> include/linux/virtio.h | 23 +-
> include/linux/virtio_ring.h | 35 +++
> lib/Makefile | 1 +
> lib/dma-noop.c | 75 ++++++
> tools/virtio/linux/dma-mapping.h | 17 ++
> 18 files changed, 594 insertions(+), 244 deletions(-)
> create mode 100644 lib/dma-noop.c
> create mode 100644 tools/virtio/linux/dma-mapping.h
>
> --
> 2.5.0
>

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