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[PATCH v6 0/9] virtio DMA API, yet again

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  [PATCH v6 0/9] virtio DMA API, yet again Andy Lutomirski <luto@kernel.org> - 2016-02-01 19:10 +0100
    [PATCH v6 9/9] vring: Use the DMA API on Xen Andy Lutomirski <luto@kernel.org> - 2016-02-01 19:10 +0100
      Re: [Xen-devel] [PATCH v6 9/9] vring: Use the DMA API on Xen Wei Liu <wei.liu2@citrix.com> - 2016-02-01 22:30 +0100
    [PATCH v6 8/9] virtio_pci: Use the DMA API if enabled Andy Lutomirski <luto@kernel.org> - 2016-02-01 19:10 +0100
    Re: [PATCH v6 0/9] virtio DMA API, yet again Christian Borntraeger <borntraeger@de.ibm.com> - 2016-02-02 11:00 +0100

#1323382 — [PATCH v6 0/9] virtio DMA API, yet again

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?

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.

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 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                   |   6 +-
 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        | 408 ++++++++++++++++++++++++++++++------
 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, 564 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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#1323384 — [PATCH v6 9/9] vring: Use the DMA API on Xen

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 drivers/virtio/virtio_ring.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index cf2840c7e500..2a921e5b1809 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -25,6 +25,7 @@
 #include <linux/hrtimer.h>
 #include <linux/kmemleak.h>
 #include <linux/dma-mapping.h>
+#include <xen/xen.h>
 
 #ifdef DEBUG
 /* For development, we want to crash whenever the ring is screwed. */
@@ -136,6 +137,17 @@ struct vring_virtqueue {
 
 static bool vring_use_dma_api(const struct vring_virtqueue *vq)
 {
+	/*
+	 * In theory, it's possible to have a buggy QEMU-supposed
+	 * emulated Q35 IOMMU and Xen enabled at the same time.  On
+	 * such a configuration, virtio has never worked and will
+	 * not work without an even larger kludge.  Instead, enable
+	 * the DMA API if we're a Xen guest, which at least allows
+	 * all of the sensible Xen configurations to work correctly.
+	 */
+	if (xen_domain())
+		return true;
+
 	return false;
 }
 
-- 
2.5.0

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#1323521 — Re: [Xen-devel] [PATCH v6 9/9] vring: Use the DMA API on Xen

On Mon, Feb 01, 2016 at 10:00:59AM -0800, Andy Lutomirski wrote:
> Signed-off-by: Andy Lutomirski <luto@kernel.org>

Reviewed-by: Wei Liu <wei.liu2@citrix.com>

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#1323385 — [PATCH v6 8/9] virtio_pci: Use the DMA API if enabled

This switches to vring_create_virtqueue, simplifying the driver and
adding DMA API support.

This fixes virtio-pci on platforms and busses that have IOMMUs.  This
will break the experimental QEMU Q35 IOMMU support until QEMU is
fixed.  In exchange, it fixes physical virtio hardware as well as
virtio-pci running under Xen.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
---
 drivers/virtio/virtio_pci_common.h |  6 ----
 drivers/virtio/virtio_pci_legacy.c | 42 +++++++++++---------------
 drivers/virtio/virtio_pci_modern.c | 61 ++++++++++----------------------------
 3 files changed, 33 insertions(+), 76 deletions(-)

diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h
index 2cc252270b2d..28263200ed42 100644
--- a/drivers/virtio/virtio_pci_common.h
+++ b/drivers/virtio/virtio_pci_common.h
@@ -35,12 +35,6 @@ struct virtio_pci_vq_info {
 	/* the actual virtqueue */
 	struct virtqueue *vq;
 
-	/* the number of entries in the queue */
-	int num;
-
-	/* the virtual address of the ring queue */
-	void *queue;
-
 	/* the list node for the virtqueues list */
 	struct list_head node;
 
diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c
index 48bc9797e530..8c4e61783441 100644
--- a/drivers/virtio/virtio_pci_legacy.c
+++ b/drivers/virtio/virtio_pci_legacy.c
@@ -119,7 +119,6 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
 				  u16 msix_vec)
 {
 	struct virtqueue *vq;
-	unsigned long size;
 	u16 num;
 	int err;
 
@@ -131,27 +130,19 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
 	if (!num || ioread32(vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN))
 		return ERR_PTR(-ENOENT);
 
-	info->num = num;
 	info->msix_vector = msix_vec;
 
-	size = PAGE_ALIGN(vring_size(num, VIRTIO_PCI_VRING_ALIGN));
-	info->queue = alloc_pages_exact(size, GFP_KERNEL|__GFP_ZERO);
-	if (info->queue == NULL)
+	/* create the vring */
+	vq = vring_create_virtqueue(index, num,
+				    VIRTIO_PCI_VRING_ALIGN, &vp_dev->vdev,
+				    true, false, vp_notify, callback, name);
+	if (!vq)
 		return ERR_PTR(-ENOMEM);
 
 	/* activate the queue */
-	iowrite32(virt_to_phys(info->queue) >> VIRTIO_PCI_QUEUE_ADDR_SHIFT,
+	iowrite32(virtqueue_get_desc_addr(vq) >> VIRTIO_PCI_QUEUE_ADDR_SHIFT,
 		  vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN);
 
-	/* create the vring */
-	vq = vring_new_virtqueue(index, info->num,
-				 VIRTIO_PCI_VRING_ALIGN, &vp_dev->vdev,
-				 true, info->queue, vp_notify, callback, name);
-	if (!vq) {
-		err = -ENOMEM;
-		goto out_activate_queue;
-	}
-
 	vq->priv = (void __force *)vp_dev->ioaddr + VIRTIO_PCI_QUEUE_NOTIFY;
 
 	if (msix_vec != VIRTIO_MSI_NO_VECTOR) {
@@ -159,17 +150,15 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
 		msix_vec = ioread16(vp_dev->ioaddr + VIRTIO_MSI_QUEUE_VECTOR);
 		if (msix_vec == VIRTIO_MSI_NO_VECTOR) {
 			err = -EBUSY;
-			goto out_assign;
+			goto out_deactivate;
 		}
 	}
 
 	return vq;
 
-out_assign:
-	vring_del_virtqueue(vq);
-out_activate_queue:
+out_deactivate:
 	iowrite32(0, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN);
-	free_pages_exact(info->queue, size);
+	vring_del_virtqueue(vq);
 	return ERR_PTR(err);
 }
 
@@ -177,7 +166,6 @@ static void del_vq(struct virtio_pci_vq_info *info)
 {
 	struct virtqueue *vq = info->vq;
 	struct virtio_pci_device *vp_dev = to_vp_device(vq->vdev);
-	unsigned long size;
 
 	iowrite16(vq->index, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_SEL);
 
@@ -188,13 +176,10 @@ static void del_vq(struct virtio_pci_vq_info *info)
 		ioread8(vp_dev->ioaddr + VIRTIO_PCI_ISR);
 	}
 
-	vring_del_virtqueue(vq);
-
 	/* Select and deactivate the queue */
 	iowrite32(0, vp_dev->ioaddr + VIRTIO_PCI_QUEUE_PFN);
 
-	size = PAGE_ALIGN(vring_size(info->num, VIRTIO_PCI_VRING_ALIGN));
-	free_pages_exact(info->queue, size);
+	vring_del_virtqueue(vq);
 }
 
 static const struct virtio_config_ops virtio_pci_config_ops = {
@@ -227,6 +212,13 @@ int virtio_pci_legacy_probe(struct virtio_pci_device *vp_dev)
 		return -ENODEV;
 	}
 
+	rc = dma_set_mask_and_coherent(&pci_dev->dev, DMA_BIT_MASK(64));
+	if (rc)
+		rc = dma_set_mask_and_coherent(&pci_dev->dev,
+						DMA_BIT_MASK(32));
+	if (rc)
+		dev_warn(&pci_dev->dev, "Failed to enable 64-bit or 32-bit DMA.  Trying to continue, but this might not work.\n");
+
 	rc = pci_request_region(pci_dev, 0, "virtio-pci-legacy");
 	if (rc)
 		return rc;
diff --git a/drivers/virtio/virtio_pci_modern.c b/drivers/virtio/virtio_pci_modern.c
index c0c11fad4611..0b4a4f440b85 100644
--- a/drivers/virtio/virtio_pci_modern.c
+++ b/drivers/virtio/virtio_pci_modern.c
@@ -287,31 +287,6 @@ static u16 vp_config_vector(struct virtio_pci_device *vp_dev, u16 vector)
 	return vp_ioread16(&vp_dev->common->msix_config);
 }
 
-static size_t vring_pci_size(u16 num)
-{
-	/* We only need a cacheline separation. */
-	return PAGE_ALIGN(vring_size(num, SMP_CACHE_BYTES));
-}
-
-static void *alloc_virtqueue_pages(int *num)
-{
-	void *pages;
-
-	/* TODO: allocate each queue chunk individually */
-	for (; *num && vring_pci_size(*num) > PAGE_SIZE; *num /= 2) {
-		pages = alloc_pages_exact(vring_pci_size(*num),
-					  GFP_KERNEL|__GFP_ZERO|__GFP_NOWARN);
-		if (pages)
-			return pages;
-	}
-
-	if (!*num)
-		return NULL;
-
-	/* Try to get a single page. You are my only hope! */
-	return alloc_pages_exact(vring_pci_size(*num), GFP_KERNEL|__GFP_ZERO);
-}
-
 static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
 				  struct virtio_pci_vq_info *info,
 				  unsigned index,
@@ -343,29 +318,22 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
 	/* get offset of notification word for this vq */
 	off = vp_ioread16(&cfg->queue_notify_off);
 
-	info->num = num;
 	info->msix_vector = msix_vec;
 
-	info->queue = alloc_virtqueue_pages(&info->num);
-	if (info->queue == NULL)
-		return ERR_PTR(-ENOMEM);
-
 	/* create the vring */
-	vq = vring_new_virtqueue(index, info->num,
-				 SMP_CACHE_BYTES, &vp_dev->vdev,
-				 true, info->queue, vp_notify, callback, name);
-	if (!vq) {
-		err = -ENOMEM;
-		goto err_new_queue;
-	}
+	vq = vring_create_virtqueue(index, num,
+				    SMP_CACHE_BYTES, &vp_dev->vdev,
+				    true, true, vp_notify, callback, name);
+	if (!vq)
+		return ERR_PTR(-ENOMEM);
 
 	/* activate the queue */
-	vp_iowrite16(num, &cfg->queue_size);
-	vp_iowrite64_twopart(virt_to_phys(info->queue),
+	vp_iowrite16(virtqueue_get_vring_size(vq), &cfg->queue_size);
+	vp_iowrite64_twopart(virtqueue_get_desc_addr(vq),
 			     &cfg->queue_desc_lo, &cfg->queue_desc_hi);
-	vp_iowrite64_twopart(virt_to_phys(virtqueue_get_avail(vq)),
+	vp_iowrite64_twopart(virtqueue_get_avail_addr(vq),
 			     &cfg->queue_avail_lo, &cfg->queue_avail_hi);
-	vp_iowrite64_twopart(virt_to_phys(virtqueue_get_used(vq)),
+	vp_iowrite64_twopart(virtqueue_get_used_addr(vq),
 			     &cfg->queue_used_lo, &cfg->queue_used_hi);
 
 	if (vp_dev->notify_base) {
@@ -410,8 +378,6 @@ err_assign_vector:
 		pci_iounmap(vp_dev->pci_dev, (void __iomem __force *)vq->priv);
 err_map_notify:
 	vring_del_virtqueue(vq);
-err_new_queue:
-	free_pages_exact(info->queue, vring_pci_size(info->num));
 	return ERR_PTR(err);
 }
 
@@ -456,8 +422,6 @@ static void del_vq(struct virtio_pci_vq_info *info)
 		pci_iounmap(vp_dev->pci_dev, (void __force __iomem *)vq->priv);
 
 	vring_del_virtqueue(vq);
-
-	free_pages_exact(info->queue, vring_pci_size(info->num));
 }
 
 static const struct virtio_config_ops virtio_pci_config_nodev_ops = {
@@ -641,6 +605,13 @@ int virtio_pci_modern_probe(struct virtio_pci_device *vp_dev)
 		return -EINVAL;
 	}
 
+	err = dma_set_mask_and_coherent(&pci_dev->dev, DMA_BIT_MASK(64));
+	if (err)
+		err = dma_set_mask_and_coherent(&pci_dev->dev,
+						DMA_BIT_MASK(32));
+	if (err)
+		dev_warn(&pci_dev->dev, "Failed to enable 64-bit or 32-bit DMA.  Trying to continue, but this might not work.\n");
+
 	/* Device capability is only mandatory for devices that have
 	 * device-specific configuration.
 	 */
-- 
2.5.0

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#1323916

On 02/01/2016 07:00 PM, 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?
> 
> 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 used your branch pub/scm/linux/kernel/git/luto/linux.git virtio_dma
on kernel.org.

It seems to survive a basic test (simple block and net) on s390 with
and without dma api enabled. No full test, though.

> 
> 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 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                   |   6 +-
>  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        | 408 ++++++++++++++++++++++++++++++------
>  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, 564 insertions(+), 244 deletions(-)
>  create mode 100644 lib/dma-noop.c
>  create mode 100644 tools/virtio/linux/dma-mapping.h
> 

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