Linux Virtualization - Feb 2019 - [PATCH v7 5/5] virtio-blk: Consider virtio_max_dma_size() for maximum segment size

Hi,

here is the next version of this patch-set. Previous
versions can be found here:

	V1: https://lore.kernel.org/lkml/20190110134433.15672-1-joro at 8bytes.org/

	V2: https://lore.kernel.org/lkml/20190115132257.6426-1-joro at 8bytes.org/

	V3: https://lore.kernel.org/lkml/20190123163049.24863-1-joro at 8bytes.org/

	V4: https://lore.kernel.org/lkml/20190129084342.26030-1-joro at 8bytes.org/

	V5: https://lore.kernel.org/lkml/20190130164007.26497-1-joro at 8bytes.org/

	V6: https://lore.kernel.org/lkml/20190131163403.11363-1-joro at 8bytes.org/

The problem solved here is a limitation of the SWIOTLB implementation,
which does not support allocations larger than 256kb.  When the
virtio-blk driver tries to read/write a block larger than that, the
allocation of the dma-handle fails and an IO error is reported.

Changes to v6 are:

	- Fix build errors with CONFIG_SWIOTLB=n

Please review.

Thanks,

	Joerg

Joerg Roedel (5):
  swiotlb: Introduce swiotlb_max_mapping_size()
  swiotlb: Add is_swiotlb_active() function
  dma: Introduce dma_max_mapping_size()
  virtio: Introduce virtio_max_dma_size()
  virtio-blk: Consider virtio_max_dma_size() for maximum segment size

 Documentation/DMA-API.txt    |  8 ++++++++
 drivers/block/virtio_blk.c   | 10 ++++++----
 drivers/virtio/virtio_ring.c | 11 +++++++++++
 include/linux/dma-mapping.h  |  8 ++++++++
 include/linux/swiotlb.h      | 11 +++++++++++
 include/linux/virtio.h       |  2 ++
 kernel/dma/direct.c          | 11 +++++++++++
 kernel/dma/mapping.c         | 14 ++++++++++++++
 kernel/dma/swiotlb.c         | 14 ++++++++++++++
 9 files changed, 85 insertions(+), 4 deletions(-)

-- 
2.17.1

From: Joerg Roedel <jroedel at suse.de>

The function returns the maximum size that can be remapped
by the SWIOTLB implementation. This function will be later
exposed to users through the DMA-API.

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
Signed-off-by: Joerg Roedel <jroedel at suse.de>
---
 include/linux/swiotlb.h | 5 +++++
 kernel/dma/swiotlb.c    | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 7c007ed7505f..d3980aeed4a0 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -76,6 +76,7 @@ bool swiotlb_map(struct device *dev, phys_addr_t *phys,
dma_addr_t *dma_addr,
 		size_t size, enum dma_data_direction dir, unsigned long attrs);
 void __init swiotlb_exit(void);
 unsigned int swiotlb_max_segment(void);
+size_t swiotlb_max_mapping_size(struct device *dev);
 #else
 #define swiotlb_force SWIOTLB_NO_FORCE
 static inline bool is_swiotlb_buffer(phys_addr_t paddr)
@@ -95,6 +96,10 @@ static inline unsigned int swiotlb_max_segment(void)
 {
 	return 0;
 }
+static inline size_t swiotlb_max_mapping_size(struct device *dev)
+{
+	return SIZE_MAX;
+}
 #endif /* CONFIG_SWIOTLB */
 
 extern void swiotlb_print_info(void);
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 1fb6fd68b9c7..9cb21259cb0b 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -662,3 +662,8 @@ swiotlb_dma_supported(struct device *hwdev, u64 mask)
 {
 	return __phys_to_dma(hwdev, io_tlb_end - 1) <= mask;
 }
+
+size_t swiotlb_max_mapping_size(struct device *dev)
+{
+	return ((size_t)1 << IO_TLB_SHIFT) * IO_TLB_SEGSIZE;
+}
-- 
2.17.1

From: Joerg Roedel <jroedel at suse.de>

This function will be used from dma_direct code to determine
the maximum segment size of a dma mapping.

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
Signed-off-by: Joerg Roedel <jroedel at suse.de>
---
 include/linux/swiotlb.h | 6 ++++++
 kernel/dma/swiotlb.c    | 9 +++++++++
 2 files changed, 15 insertions(+)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index d3980aeed4a0..29bc3a203283 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -77,6 +77,7 @@ bool swiotlb_map(struct device *dev, phys_addr_t *phys,
dma_addr_t *dma_addr,
 void __init swiotlb_exit(void);
 unsigned int swiotlb_max_segment(void);
 size_t swiotlb_max_mapping_size(struct device *dev);
+bool is_swiotlb_active(void);
 #else
 #define swiotlb_force SWIOTLB_NO_FORCE
 static inline bool is_swiotlb_buffer(phys_addr_t paddr)
@@ -100,6 +101,11 @@ static inline size_t swiotlb_max_mapping_size(struct device
*dev)
 {
 	return SIZE_MAX;
 }
+
+static inline bool is_swiotlb_active(void)
+{
+	return false;
+}
 #endif /* CONFIG_SWIOTLB */
 
 extern void swiotlb_print_info(void);
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 9cb21259cb0b..c873f9cc2146 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -667,3 +667,12 @@ size_t swiotlb_max_mapping_size(struct device *dev)
 {
 	return ((size_t)1 << IO_TLB_SHIFT) * IO_TLB_SEGSIZE;
 }
+
+bool is_swiotlb_active(void)
+{
+	/*
+	 * When SWIOTLB is initialized, even if io_tlb_start points to physical
+	 * address zero, io_tlb_end surely doesn't.
+	 */
+	return io_tlb_end != 0;
+}
-- 
2.17.1

From: Joerg Roedel <jroedel at suse.de>

The function returns the maximum size that can be mapped
using DMA-API functions. The patch also adds the
implementation for direct DMA and a new dma_map_ops pointer
so that other implementations can expose their limit.

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
Signed-off-by: Joerg Roedel <jroedel at suse.de>
---
 Documentation/DMA-API.txt   |  8 ++++++++
 include/linux/dma-mapping.h |  8 ++++++++
 kernel/dma/direct.c         | 11 +++++++++++
 kernel/dma/mapping.c        | 14 ++++++++++++++
 4 files changed, 41 insertions(+)

diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt
index e133ccd60228..acfe3d0f78d1 100644
--- a/Documentation/DMA-API.txt
+++ b/Documentation/DMA-API.txt
@@ -195,6 +195,14 @@ Requesting the required mask does not alter the current
mask.  If you
 wish to take advantage of it, you should issue a dma_set_mask()
 call to set the mask to the value returned.
 
+::
+
+	size_t
+	dma_direct_max_mapping_size(struct device *dev);
+
+Returns the maximum size of a mapping for the device. The size parameter
+of the mapping functions like dma_map_single(), dma_map_page() and
+others should not be larger than the returned value.
 
 Part Id - Streaming DMA mappings
 --------------------------------
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index f6ded992c183..5b21f14802e1 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -130,6 +130,7 @@ struct dma_map_ops {
 			enum dma_data_direction direction);
 	int (*dma_supported)(struct device *dev, u64 mask);
 	u64 (*get_required_mask)(struct device *dev);
+	size_t (*max_mapping_size)(struct device *dev);
 };
 
 #define DMA_MAPPING_ERROR		(~(dma_addr_t)0)
@@ -257,6 +258,8 @@ static inline void dma_direct_sync_sg_for_cpu(struct device
*dev,
 }
 #endif
 
+size_t dma_direct_max_mapping_size(struct device *dev);
+
 #ifdef CONFIG_HAS_DMA
 #include <asm/dma-mapping.h>
 
@@ -460,6 +463,7 @@ int dma_supported(struct device *dev, u64 mask);
 int dma_set_mask(struct device *dev, u64 mask);
 int dma_set_coherent_mask(struct device *dev, u64 mask);
 u64 dma_get_required_mask(struct device *dev);
+size_t dma_max_mapping_size(struct device *dev);
 #else /* CONFIG_HAS_DMA */
 static inline dma_addr_t dma_map_page_attrs(struct device *dev,
 		struct page *page, size_t offset, size_t size,
@@ -561,6 +565,10 @@ static inline u64 dma_get_required_mask(struct device *dev)
 {
 	return 0;
 }
+static inline size_t dma_max_mapping_size(struct device *dev)
+{
+	return 0;
+}
 #endif /* CONFIG_HAS_DMA */
 
 static inline dma_addr_t dma_map_single_attrs(struct device *dev, void *ptr,
diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 355d16acee6d..6310ad01f915 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -380,3 +380,14 @@ int dma_direct_supported(struct device *dev, u64 mask)
 	 */
 	return mask >= __phys_to_dma(dev, min_mask);
 }
+
+size_t dma_direct_max_mapping_size(struct device *dev)
+{
+	size_t size = SIZE_MAX;
+
+	/* If SWIOTLB is active, use its maximum mapping size */
+	if (is_swiotlb_active())
+		size = swiotlb_max_mapping_size(dev);
+
+	return size;
+}
diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
index a11006b6d8e8..5753008ab286 100644
--- a/kernel/dma/mapping.c
+++ b/kernel/dma/mapping.c
@@ -357,3 +357,17 @@ void dma_cache_sync(struct device *dev, void *vaddr, size_t
size,
 		ops->cache_sync(dev, vaddr, size, dir);
 }
 EXPORT_SYMBOL(dma_cache_sync);
+
+size_t dma_max_mapping_size(struct device *dev)
+{
+	const struct dma_map_ops *ops = get_dma_ops(dev);
+	size_t size = SIZE_MAX;
+
+	if (dma_is_direct(ops))
+		size = dma_direct_max_mapping_size(dev);
+	else if (ops && ops->max_mapping_size)
+		size = ops->max_mapping_size(dev);
+
+	return size;
+}
+EXPORT_SYMBOL_GPL(dma_max_mapping_size);
-- 
2.17.1

From: Joerg Roedel <jroedel at suse.de>

This function returns the maximum segment size for a single
dma transaction of a virtio device. The possible limit comes
from the SWIOTLB implementation in the Linux kernel, that
has an upper limit of (currently) 256kb of contiguous
memory it can map. Other DMA-API implementations might also
have limits.

Use the new dma_max_mapping_size() function to determine the
maximum mapping size when DMA-API is in use for virtio.

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
Signed-off-by: Joerg Roedel <jroedel at suse.de>
---
 drivers/virtio/virtio_ring.c | 11 +++++++++++
 include/linux/virtio.h       |  2 ++
 2 files changed, 13 insertions(+)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index cd7e755484e3..8a31c6862b2b 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -266,6 +266,17 @@ static bool vring_use_dma_api(struct virtio_device *vdev)
 	return false;
 }
 
+size_t virtio_max_dma_size(struct virtio_device *vdev)
+{
+	size_t max_segment_size = SIZE_MAX;
+
+	if (vring_use_dma_api(vdev))
+		max_segment_size = dma_max_mapping_size(&vdev->dev);
+
+	return max_segment_size;
+}
+EXPORT_SYMBOL_GPL(virtio_max_dma_size);
+
 static void *vring_alloc_queue(struct virtio_device *vdev, size_t size,
 			      dma_addr_t *dma_handle, gfp_t flag)
 {
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index fa1b5da2804e..673fe3ef3607 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -157,6 +157,8 @@ int virtio_device_freeze(struct virtio_device *dev);
 int virtio_device_restore(struct virtio_device *dev);
 #endif
 
+size_t virtio_max_dma_size(struct virtio_device *vdev);
+
 #define virtio_device_for_each_vq(vdev, vq) \
 	list_for_each_entry(vq, &vdev->vqs, list)
 
-- 
2.17.1

From: Joerg Roedel <jroedel at suse.de>

Segments can't be larger than the maximum DMA mapping size
supported on the platform. Take that into account when
setting the maximum segment size for a block device.

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
Reviewed-by: Christoph Hellwig <hch at lst.de>
Signed-off-by: Joerg Roedel <jroedel at suse.de>
---
 drivers/block/virtio_blk.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index b16a887bbd02..4bc083b7c9b5 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -723,7 +723,7 @@ static int virtblk_probe(struct virtio_device *vdev)
 	struct request_queue *q;
 	int err, index;
 
-	u32 v, blk_size, sg_elems, opt_io_size;
+	u32 v, blk_size, max_size, sg_elems, opt_io_size;
 	u16 min_io_size;
 	u8 physical_block_exp, alignment_offset;
 
@@ -826,14 +826,16 @@ static int virtblk_probe(struct virtio_device *vdev)
 	/* No real sector limit. */
 	blk_queue_max_hw_sectors(q, -1U);
 
+	max_size = virtio_max_dma_size(vdev);
+
 	/* Host can optionally specify maximum segment size and number of
 	 * segments. */
 	err = virtio_cread_feature(vdev, VIRTIO_BLK_F_SIZE_MAX,
 				   struct virtio_blk_config, size_max, &v);
 	if (!err)
-		blk_queue_max_segment_size(q, v);
-	else
-		blk_queue_max_segment_size(q, -1U);
+		max_size = min(max_size, v);
+
+	blk_queue_max_segment_size(q, max_size);
 
 	/* Host can optionally specify the block size of the device */
 	err = virtio_cread_feature(vdev, VIRTIO_BLK_F_BLK_SIZE,
-- 
2.17.1