[PATCH v5 1/3] virtio_ring: Support DMA APIs if requested

Andy Lutomirski
2014-09-17T05:22:26Z

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. virtio-net warns (correctly) about DMA from
the stack in virtnet_set_rx_mode.

This explicitly supports !CONFIG_HAS_DMA. If vring is asked to use
the DMA API and CONFIG_HAS_DMA is not set, then vring will refuse to
create the virtqueue.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
---
drivers/lguest/lguest_device.c | 3 +-
drivers/misc/mic/card/mic_virtio.c | 2 +-
drivers/remoteproc/remoteproc_virtio.c | 4 +-
drivers/s390/kvm/kvm_virtio.c | 2 +-
drivers/s390/kvm/virtio_ccw.c | 4 +-
drivers/virtio/virtio_mmio.c | 5 +-
drivers/virtio/virtio_pci.c | 3 +-
drivers/virtio/virtio_ring.c | 194 +++++++++++++++++++++++++++------
include/linux/virtio_ring.h | 1 +
tools/virtio/linux/dma-mapping.h | 17 +++
tools/virtio/linux/virtio.h | 1 +
tools/virtio/virtio_test.c | 2 +-
tools/virtio/vringh_test.c | 3 +-
13 files changed, 198 insertions(+), 43 deletions(-)
create mode 100644 tools/virtio/linux/dma-mapping.h

diff --git a/drivers/lguest/lguest_device.c b/drivers/lguest/lguest_device.c
index d0a1d8a45c81..f0eafbe82ed4 100644
--- a/drivers/lguest/lguest_device.c
+++ b/drivers/lguest/lguest_device.c
@@ -301,7 +301,8 @@ static struct virtqueue *lg_find_vq(struct virtio_device *vdev,
* barriers.
*/
vq = vring_new_virtqueue(index, lvq->config.num, LGUEST_VRING_ALIGN, vdev,
- true, lvq->pages, lg_notify, callback, name);
+ true, false, lvq->pages,
+ lg_notify, callback, name);
if (!vq) {
err = -ENOMEM;
goto unmap;
diff --git a/drivers/misc/mic/card/mic_virtio.c b/drivers/misc/mic/card/mic_virtio.c
index f14b60080c21..d633964417b1 100644
--- a/drivers/misc/mic/card/mic_virtio.c
+++ b/drivers/misc/mic/card/mic_virtio.c
@@ -256,7 +256,7 @@ static struct virtqueue *mic_find_vq(struct virtio_device *vdev,
mvdev->vr[index] = va;
memset_io(va, 0x0, _vr_size);
vq = vring_new_virtqueue(index, le16_to_cpu(config.num),
- MIC_VIRTIO_RING_ALIGN, vdev, false,
+ MIC_VIRTIO_RING_ALIGN, vdev, false, false,
(void __force *)va, mic_notify, callback,
name);
if (!vq) {
diff --git a/drivers/remoteproc/remoteproc_virtio.c b/drivers/remoteproc/remoteproc_virtio.c
index a34b50690b4e..e31f2fefa76e 100644
--- a/drivers/remoteproc/remoteproc_virtio.c
+++ b/drivers/remoteproc/remoteproc_virtio.c
@@ -107,8 +107,8 @@ static struct virtqueue *rp_find_vq(struct virtio_device *vdev,
* Create the new vq, and tell virtio we're not interested in
* the 'weak' smp barriers, since we're talking with a real device.
*/
- vq = vring_new_virtqueue(id, len, rvring->align, vdev, false, addr,
- rproc_virtio_notify, callback, name);
+ vq = vring_new_virtqueue(id, len, rvring->align, vdev, false, false,
+ addr, rproc_virtio_notify, callback, name);
if (!vq) {
dev_err(dev, "vring_new_virtqueue %s failed\n", name);
rproc_free_vring(rvring);
diff --git a/drivers/s390/kvm/kvm_virtio.c b/drivers/s390/kvm/kvm_virtio.c
index a1349653c6d9..91abcdc196d0 100644
--- a/drivers/s390/kvm/kvm_virtio.c
+++ b/drivers/s390/kvm/kvm_virtio.c
@@ -206,7 +206,7 @@ static struct virtqueue *kvm_find_vq(struct virtio_device *vdev,
goto out;

vq = vring_new_virtqueue(index, config->num, KVM_S390_VIRTIO_RING_ALIGN,
- vdev, true, (void *) config->address,
+ vdev, true, false, (void *) config->address,
kvm_notify, callback, name);
if (!vq) {
err = -ENOMEM;
diff --git a/drivers/s390/kvm/virtio_ccw.c b/drivers/s390/kvm/virtio_ccw.c
index d2c0b442bce5..2462a443358a 100644
--- a/drivers/s390/kvm/virtio_ccw.c
+++ b/drivers/s390/kvm/virtio_ccw.c
@@ -478,8 +478,8 @@ static struct virtqueue *virtio_ccw_setup_vq(struct virtio_device *vdev,
}

vq = vring_new_virtqueue(i, info->num, KVM_VIRTIO_CCW_RING_ALIGN, vdev,
- true, info->queue, virtio_ccw_kvm_notify,
- callback, name);
+ true, false, info->queue,
+ virtio_ccw_kvm_notify, callback, name);
if (!vq) {
/* For now, we fail if we can't get the requested size. */
dev_warn(&vcdev->cdev->dev, "no vq\n");
diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index c600ccfd6922..693254e52a5d 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c
@@ -366,8 +366,9 @@ static struct virtqueue *vm_setup_vq(struct virtio_device *vdev, unsigned index,
vm_dev->base + VIRTIO_MMIO_QUEUE_PFN);

/* Create the vring */
- vq = vring_new_virtqueue(index, info->num, VIRTIO_MMIO_VRING_ALIGN, vdev,
- true, info->queue, vm_notify, callback, name);
+ vq = vring_new_virtqueue(index, info->num, VIRTIO_MMIO_VRING_ALIGN,
+ vdev, true, false, info->queue,
+ vm_notify, callback, name);
if (!vq) {
err = -ENOMEM;
goto error_new_virtqueue;
diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index 3d1463c6b120..a1f299fa4626 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -430,7 +430,8 @@ static struct virtqueue *setup_vq(struct virtio_device *vdev, unsigned index,

/* create the vring */
vq = vring_new_virtqueue(index, info->num, VIRTIO_PCI_VRING_ALIGN, vdev,
- true, info->queue, vp_notify, callback, name);
+ true, false, info->queue,
+ vp_notify, callback, name);
if (!vq) {
err = -ENOMEM;
goto out_activate_queue;
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 3b1f89b6e743..babcaea1afa0 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -24,6 +24,7 @@
#include <linux/module.h>
#include <linux/hrtimer.h>
#include <linux/kmemleak.h>
+#include <linux/dma-mapping.h>

#ifdef DEBUG
/* For development, we want to crash whenever the ring is screwed. */
@@ -54,6 +55,12 @@
#define END_USE(vq)
#endif

+struct vring_desc_state
+{
+ void *data; /* Data for callback. */
+ struct vring_desc *indir_desc; /* Indirect descriptor, if any. */
+};
+
struct vring_virtqueue
{
struct virtqueue vq;
@@ -64,6 +71,9 @@ struct vring_virtqueue
/* Can we use weak barriers? */
bool weak_barriers;

+ /* Should we use the DMA API? */
+ bool use_dma_api;
+
/* Other side has made a mess, don't try any more. */
bool broken;

@@ -93,12 +103,81 @@ struct vring_virtqueue
ktime_t last_add_time;
#endif

- /* Tokens for callbacks. */
- void *data[];
+ /* Per-descriptor state. */
+ struct vring_desc_state desc_state[];
};

#define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)

+/* Map one sg entry. */
+static dma_addr_t vring_map_one_sg(const struct vring_virtqueue *vq,
+ struct scatterlist *sg,
+ enum dma_data_direction direction)
+{
+#ifdef CONFIG_HAS_DMA
+ /*
+ * We can't use dma_map_sg, because we don't use scatterlists in
+ * the way it expects (we sometimes use unterminated
+ * scatterlists, and we don't guarantee that the scatterlist
+ * will exist for the lifetime of the mapping.
+ */
+ if (vq->use_dma_api)
+ return dma_map_page(vq->vq.vdev->dev.parent,
+ sg_page(sg), sg->offset, sg->length,
+ direction);
+#endif
+
+ return sg_phys(sg);
+}
+
+static dma_addr_t vring_map_single(const struct vring_virtqueue *vq,
+ void *cpu_addr, size_t size,
+ enum dma_data_direction direction)
+{
+#ifdef CONFIG_HAS_DMA
+ if (vq->use_dma_api)
+ return dma_map_single(vq->vq.vdev->dev.parent,
+ cpu_addr, size,
+ direction);
+#endif
+
+ /* avoid kmemleak false positive (hidden by virt_to_phys) */
+ kmemleak_ignore(cpu_addr);
+ return virt_to_phys(cpu_addr);
+}
+
+static void vring_unmap_one(const struct vring_virtqueue *vq,
+ struct vring_desc *desc)
+{
+#ifdef CONFIG_HAS_DMA
+ if (!vq->use_dma_api)
+ return; /* Nothing to do. */
+
+ if (desc->flags & VRING_DESC_F_INDIRECT) {
+ dma_unmap_single(vq->vq.vdev->dev.parent,
+ desc->addr, desc->len,
+ (desc->flags & VRING_DESC_F_WRITE) ?
+ DMA_FROM_DEVICE : DMA_TO_DEVICE);
+ } else {
+ dma_unmap_page(vq->vq.vdev->dev.parent,
+ desc->addr, desc->len,
+ (desc->flags & VRING_DESC_F_WRITE) ?
+ DMA_FROM_DEVICE : DMA_TO_DEVICE);
+ }
+#endif
+}
+
+static int vring_mapping_error(const struct vring_virtqueue *vq,
+ dma_addr_t addr)
+{
+#ifdef CONFIG_HAS_DMA
+ return vq->use_dma_api &&
+ dma_mapping_error(vq->vq.vdev->dev.parent, addr);
+#else
+ return 0;
+#endif
+}
+
static struct vring_desc *alloc_indirect(unsigned int total_sg, gfp_t gfp)
{
struct vring_desc *desc;
@@ -131,7 +210,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
struct vring_virtqueue *vq = to_vvq(_vq);
struct scatterlist *sg;
struct vring_desc *desc;
- unsigned int i, n, avail, descs_used, uninitialized_var(prev);
+ unsigned int i, n, avail, descs_used, uninitialized_var(prev), err_idx;
int head;
bool indirect;

@@ -171,21 +250,25 @@ static inline int virtqueue_add(struct virtqueue *_vq,

if (desc) {
/* Use a single buffer which doesn't continue */
+ indirect = true;
vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
- vq->vring.desc[head].addr = virt_to_phys(desc);
- /* avoid kmemleak false positive (hidden by virt_to_phys) */
- kmemleak_ignore(desc);
+ vq->vring.desc[head].addr = vring_map_single(
+ vq,
+ desc, total_sg * sizeof(struct vring_desc),
+ DMA_TO_DEVICE);
+ if (vring_mapping_error(vq, vq->vring.desc[head].addr))
+ goto unmap_free_indir;
+
vq->vring.desc[head].len = total_sg * sizeof(struct vring_desc);

/* Set up rest to use this indirect table. */
i = 0;
descs_used = 1;
- indirect = true;
} else {
+ indirect = false;
desc = vq->vring.desc;
i = head;
descs_used = total_sg;
- indirect = false;
}

if (vq->vq.num_free < descs_used) {
@@ -200,14 +283,13 @@ static inline int virtqueue_add(struct virtqueue *_vq,
return -ENOSPC;
}

- /* We're about to use some buffers from the free list. */
- vq->vq.num_free -= descs_used;
-
for (n = 0; n < out_sgs; n++) {
for (sg = sgs[n]; sg; sg = sg_next(sg)) {
desc[i].flags = VRING_DESC_F_NEXT;
- desc[i].addr = sg_phys(sg);
+ desc[i].addr = vring_map_one_sg(vq, sg, DMA_TO_DEVICE);
desc[i].len = sg->length;
+ if (vring_mapping_error(vq, desc[i].addr))
+ goto unmap_release;
prev = i;
i = desc[i].next;
}
@@ -215,8 +297,10 @@ static inline int virtqueue_add(struct virtqueue *_vq,
for (; n < (out_sgs + in_sgs); n++) {
for (sg = sgs[n]; sg; sg = sg_next(sg)) {
desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
- desc[i].addr = sg_phys(sg);
+ desc[i].addr = vring_map_one_sg(vq, sg, DMA_FROM_DEVICE);
desc[i].len = sg->length;
+ if (vring_mapping_error(vq, desc[i].addr))
+ goto unmap_release;
prev = i;
i = desc[i].next;
}
@@ -224,14 +308,19 @@ static inline int virtqueue_add(struct virtqueue *_vq,
/* Last one doesn't continue. */
desc[prev].flags &= ~VRING_DESC_F_NEXT;

+ /* We're using some buffers from the free list. */
+ vq->vq.num_free -= descs_used;
+
/* Update free pointer */
if (indirect)
vq->free_head = vq->vring.desc[head].next;
else
vq->free_head = i;

- /* Set token. */
- vq->data[head] = data;
+ /* Store token and indirect buffer state. */
+ vq->desc_state[head].data = data;
+ if (indirect)
+ vq->desc_state[head].indir_desc = desc;

/* Put entry in available array (but don't update avail->idx until they
* do sync). */
@@ -253,6 +342,28 @@ static inline int virtqueue_add(struct virtqueue *_vq,
END_USE(vq);

return 0;
+
+unmap_release:
+ err_idx = i;
+ i = head;
+
+ for (n = 0; n < total_sg; n++) {
+ if (i == err_idx)
+ break;
+ vring_unmap_one(vq, &desc[i]);
+ i = vq->vring.desc[i].next;
+ }
+
+ vq->vq.num_free += total_sg;
+
+ if (indirect)
+ vring_unmap_one(vq, desc);
+
+unmap_free_indir:
+ if (indirect)
+ kfree(desc);
+
+ return -EIO;
}

/**
@@ -423,27 +534,42 @@ EXPORT_SYMBOL_GPL(virtqueue_kick);

static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
{
- unsigned int i;
+ unsigned int i, j;

/* 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 & VRING_DESC_F_INDIRECT)
- kfree(phys_to_virt(vq->vring.desc[i].addr));
-
while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) {
+ vring_unmap_one(vq, &vq->vring.desc[i]);
i = vq->vring.desc[i].next;
vq->vq.num_free++;
}

+ vring_unmap_one(vq, &vq->vring.desc[i]);
vq->vring.desc[i].next = 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;
+
+ BUG_ON(!(vq->vring.desc[head].flags & VRING_DESC_F_INDIRECT));
+ BUG_ON(len == 0 || len % sizeof(struct vring_desc));
+
+ if (vq->use_dma_api)
+ 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;
+ }
}

static inline bool more_used(const struct vring_virtqueue *vq)
@@ -498,13 +624,13 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
BAD_RING(vq, "id %u out of range\n", i);
return NULL;
}
- if (unlikely(!vq->data[i])) {
+ if (unlikely(!vq->desc_state[i].data)) {
BAD_RING(vq, "id %u is not a head!\n", i);
return NULL;
}

/* detach_buf clears data, so grab it now. */
- ret = vq->data[i];
+ ret = vq->desc_state[i].data;
detach_buf(vq, i);
vq->last_used_idx++;
/* If we expect an interrupt for the next entry, tell host
@@ -665,10 +791,10 @@ void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
START_USE(vq);

for (i = 0; i < vq->vring.num; i++) {
- if (!vq->data[i])
+ if (!vq->desc_state[i].data)
continue;
/* detach_buf clears data, so grab it now. */
- buf = vq->data[i];
+ buf = vq->desc_state[i].data;
detach_buf(vq, i);
vq->vring.avail->idx--;
END_USE(vq);
@@ -707,6 +833,7 @@ struct virtqueue *vring_new_virtqueue(unsigned int index,
unsigned int vring_align,
struct virtio_device *vdev,
bool weak_barriers,
+ bool use_dma_api,
void *pages,
bool (*notify)(struct virtqueue *),
void (*callback)(struct virtqueue *),
@@ -721,7 +848,13 @@ struct virtqueue *vring_new_virtqueue(unsigned int index,
return NULL;
}

- vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL);
+#ifndef CONFIG_HAS_DMA
+ if (use_dma_api)
+ return NULL;
+#endif
+
+ vq = kmalloc(sizeof(*vq) + num * sizeof(struct vring_desc_state),
+ GFP_KERNEL);
if (!vq)
return NULL;

@@ -733,6 +866,7 @@ struct virtqueue *vring_new_virtqueue(unsigned int index,
vq->vq.index = index;
vq->notify = notify;
vq->weak_barriers = weak_barriers;
+ vq->use_dma_api = use_dma_api;
vq->broken = false;
vq->last_used_idx = 0;
vq->num_added = 0;
@@ -751,11 +885,9 @@ struct virtqueue *vring_new_virtqueue(unsigned int index,

/* Put everything in free lists. */
vq->free_head = 0;
- for (i = 0; i < num-1; i++) {
+ for (i = 0; i < num-1; i++)
vq->vring.desc[i].next = i+1;
- vq->data[i] = NULL;
- }
- vq->data[i] = NULL;
+ memset(vq->desc_state, 0, num * sizeof(struct vring_desc_state));

return &vq->vq;
}
diff --git a/include/linux/virtio_ring.h b/include/linux/virtio_ring.h
index 67e06fe18c03..60f761a38a09 100644
--- a/include/linux/virtio_ring.h
+++ b/include/linux/virtio_ring.h
@@ -70,6 +70,7 @@ struct virtqueue *vring_new_virtqueue(unsigned int index,
unsigned int vring_align,
struct virtio_device *vdev,
bool weak_barriers,
+ bool use_dma_api,
void *pages,
bool (*notify)(struct virtqueue *vq),
void (*callback)(struct virtqueue *vq),
diff --git a/tools/virtio/linux/dma-mapping.h b/tools/virtio/linux/dma-mapping.h
new file mode 100644
index 000000000000..4f93af89ae16
--- /dev/null
+++ b/tools/virtio/linux/dma-mapping.h
@@ -0,0 +1,17 @@
+#ifndef _LINUX_DMA_MAPPING_H
+#define _LINUX_DMA_MAPPING_H
+
+#ifdef CONFIG_HAS_DMA
+# error Virtio userspace code does not support CONFIG_HAS_DMA
+#endif
+
+#define PCI_DMA_BUS_IS_PHYS 1
+
+enum dma_data_direction {
+ DMA_BIDIRECTIONAL = 0,
+ DMA_TO_DEVICE = 1,
+ DMA_FROM_DEVICE = 2,
+ DMA_NONE = 3,
+};
+
+#endif
diff --git a/tools/virtio/linux/virtio.h b/tools/virtio/linux/virtio.h
index 5a2d1f0f6bc7..5d42dc6a6201 100644
--- a/tools/virtio/linux/virtio.h
+++ b/tools/virtio/linux/virtio.h
@@ -78,6 +78,7 @@ struct virtqueue *vring_new_virtqueue(unsigned int index,
unsigned int vring_align,
struct virtio_device *vdev,
bool weak_barriers,
+ bool use_dma_api,
void *pages,
bool (*notify)(struct virtqueue *vq),
void (*callback)(struct virtqueue *vq),
diff --git a/tools/virtio/virtio_test.c b/tools/virtio/virtio_test.c
index 00ea679b3826..860cc89900a7 100644
--- a/tools/virtio/virtio_test.c
+++ b/tools/virtio/virtio_test.c
@@ -99,7 +99,7 @@ static void vq_info_add(struct vdev_info *dev, int num)
vring_init(&info->vring, num, info->ring, 4096);
info->vq = vring_new_virtqueue(info->idx,
info->vring.num, 4096, &dev->vdev,
- true, info->ring,
+ true, false, info->ring,
vq_notify, vq_callback, "test");
assert(info->vq);
info->vq->priv = info;
diff --git a/tools/virtio/vringh_test.c b/tools/virtio/vringh_test.c
index 14a4f4cab5b9..67d3c3a1ba88 100644
--- a/tools/virtio/vringh_test.c
+++ b/tools/virtio/vringh_test.c
@@ -312,7 +312,8 @@ static int parallel_test(unsigned long features,
if (sched_setaffinity(getpid(), sizeof(cpu_set), &cpu_set))
err(1, "Could not set affinity to cpu %u", first_cpu);

- vq = vring_new_virtqueue(0, RINGSIZE, ALIGN, &gvdev.vdev, true,
+ vq = vring_new_virtqueue(0, RINGSIZE, ALIGN, &gvdev.vdev,
+ true, false,
guest_map, fast_vringh ? no_notify_host
: parallel_notify_host,
never_callback_guest, "guest vq");
--
1.9.3