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Subject[PATCH v2 6/6] dma-buf: heaps: Skip sync if not mapped
Date
This patch is basically a port of Ørjan Eide's similar patch for ION
https://lore.kernel.org/lkml/20200414134629.54567-1-orjan.eide@arm.com/

Only sync the sg-list of dma-buf heap attachment when the attachment
is actually mapped on the device.

dma-bufs may be synced at any time. It can be reached from user space
via DMA_BUF_IOCTL_SYNC, so there are no guarantees from callers on when
syncs may be attempted, and dma_buf_end_cpu_access() and
dma_buf_begin_cpu_access() may not be paired.

Since the sg_list's dma_address isn't set up until the buffer is used
on the device, and dma_map_sg() is called on it, the dma_address will be
NULL if sync is attempted on the dma-buf before it's mapped on a device.

Before v5.0 (commit 55897af63091 ("dma-direct: merge swiotlb_dma_ops
into the dma_direct code")) this was a problem as the dma-api (at least
the swiotlb_dma_ops on arm64) would use the potentially invalid
dma_address. How that failed depended on how the device handled physical
address 0. If 0 was a valid address to physical ram, that page would get
flushed a lot, while the actual pages in the buffer would not get synced
correctly. While if 0 is an invalid physical address it may cause a
fault and trigger a crash.

In v5.0 this was incidentally fixed by commit 55897af63091 ("dma-direct:
merge swiotlb_dma_ops into the dma_direct code"), as this moved the
dma-api to use the page pointer in the sg_list, and (for Ion buffers at
least) this will always be valid if the sg_list exists at all.

But, this issue is re-introduced in v5.3 with
commit 449fa54d6815 ("dma-direct: correct the physical addr in
dma_direct_sync_sg_for_cpu/device") moves the dma-api back to the old
behaviour and picks the dma_address that may be invalid.

dma-buf core doesn't ensure that the buffer is mapped on the device, and
thus have a valid sg_list, before calling the exporter's
begin_cpu_access.

Logic and commit message originally by: Ørjan Eide <orjan.eide@arm.com>

Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Liam Mark <lmark@codeaurora.org>
Cc: Laura Abbott <labbott@kernel.org>
Cc: Brian Starkey <Brian.Starkey@arm.com>
Cc: Hridya Valsaraju <hridya@google.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Sandeep Patil <sspatil@google.com>
Cc: Ørjan Eide <orjan.eide@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Ezequiel Garcia <ezequiel@collabora.com>
Cc: Simon Ser <contact@emersion.fr>
Cc: James Jones <jajones@nvidia.com>
Cc: linux-media@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
drivers/dma-buf/heaps/cma_heap.c | 10 ++++++++++
drivers/dma-buf/heaps/system_heap.c | 10 ++++++++++
2 files changed, 20 insertions(+)

diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
index 4f20f07872e5..e19320f52063 100644
--- a/drivers/dma-buf/heaps/cma_heap.c
+++ b/drivers/dma-buf/heaps/cma_heap.c
@@ -44,6 +44,7 @@ struct dma_heap_attachment {
struct device *dev;
struct sg_table table;
struct list_head list;
+ bool mapped;
};

static int cma_heap_attach(struct dma_buf *dmabuf,
@@ -68,6 +69,7 @@ static int cma_heap_attach(struct dma_buf *dmabuf,

a->dev = attachment->dev;
INIT_LIST_HEAD(&a->list);
+ a->mapped = false;

attachment->priv = a;

@@ -101,6 +103,7 @@ static struct sg_table *cma_heap_map_dma_buf(struct dma_buf_attachment *attachme
if (!dma_map_sg(attachment->dev, table->sgl, table->nents,
direction))
table = ERR_PTR(-ENOMEM);
+ a->mapped = true;
return table;
}

@@ -108,6 +111,9 @@ static void cma_heap_unmap_dma_buf(struct dma_buf_attachment *attachment,
struct sg_table *table,
enum dma_data_direction direction)
{
+ struct dma_heap_attachment *a = attachment->priv;
+
+ a->mapped = false;
dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);
}

@@ -122,6 +128,8 @@ static int cma_heap_dma_buf_begin_cpu_access(struct dma_buf *dmabuf,

mutex_lock(&buffer->lock);
list_for_each_entry(a, &buffer->attachments, list) {
+ if (!a->mapped)
+ continue;
dma_sync_sg_for_cpu(a->dev, a->table.sgl, a->table.nents,
direction);
}
@@ -141,6 +149,8 @@ static int cma_heap_dma_buf_end_cpu_access(struct dma_buf *dmabuf,

mutex_lock(&buffer->lock);
list_for_each_entry(a, &buffer->attachments, list) {
+ if (!a->mapped)
+ continue;
dma_sync_sg_for_device(a->dev, a->table.sgl, a->table.nents,
direction);
}
diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
index f30904345cce..c0d051203300 100644
--- a/drivers/dma-buf/heaps/system_heap.c
+++ b/drivers/dma-buf/heaps/system_heap.c
@@ -38,6 +38,7 @@ struct dma_heap_attachment {
struct device *dev;
struct sg_table *table;
struct list_head list;
+ bool mapped;
};

#define HIGH_ORDER_GFP (((GFP_HIGHUSER | __GFP_ZERO | __GFP_NOWARN \
@@ -94,6 +95,7 @@ static int system_heap_attach(struct dma_buf *dmabuf,
a->table = table;
a->dev = attachment->dev;
INIT_LIST_HEAD(&a->list);
+ a->mapped = false;

attachment->priv = a;

@@ -128,6 +130,7 @@ static struct sg_table *system_heap_map_dma_buf(struct dma_buf_attachment *attac
if (!dma_map_sg(attachment->dev, table->sgl, table->nents, direction))
return ERR_PTR(-ENOMEM);

+ a->mapped = true;
return table;
}

@@ -135,6 +138,9 @@ static void system_heap_unmap_dma_buf(struct dma_buf_attachment *attachment,
struct sg_table *table,
enum dma_data_direction direction)
{
+ struct dma_heap_attachment *a = attachment->priv;
+
+ a->mapped = false;
dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);
}

@@ -150,6 +156,8 @@ static int system_heap_dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
invalidate_kernel_vmap_range(buffer->vaddr, buffer->len);

list_for_each_entry(a, &buffer->attachments, list) {
+ if (!a->mapped)
+ continue;
dma_sync_sg_for_cpu(a->dev, a->table->sgl, a->table->nents,
direction);
}
@@ -170,6 +178,8 @@ static int system_heap_dma_buf_end_cpu_access(struct dma_buf *dmabuf,
flush_kernel_vmap_range(buffer->vaddr, buffer->len);

list_for_each_entry(a, &buffer->attachments, list) {
+ if (!a->mapped)
+ continue;
dma_sync_sg_for_device(a->dev, a->table->sgl, a->table->nents,
direction);
}
--
2.17.1
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