[PATCH net-next v4 4/5] page_pool: disable sync for cpu for dmabuf memory provider

[Mina Almasry <almasrymina@xxxxxxxxxx>]

dmabuf dma-addresses should not be dma_sync'd for CPU/device. Typically
its the driver responsibility to dma_sync for CPU, but the driver should
not dma_sync for CPU if the netmem is actually coming from a dmabuf
memory provider.

The page_pool already exposes a helper for dma_sync_for_cpu:
page_pool_dma_sync_for_cpu. Upgrade this existing helper to handle
netmem, and have it skip dma_sync if the memory is from a dmabuf memory
provider. Drivers should migrate to using this helper when adding
support for netmem.

Also minimize the impact on the dma syncing performance for pages. Special
case the dma-sync path for pages to not go through the overhead checks
for dma-syncing and conversion to netmem.

Cc: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxx>
Signed-off-by: Mina Almasry <almasrymina@xxxxxxxxxx>

---

v4:
- Special case pages to reduce perf overhead (Jakub)
- Add page_pool flag to set dma syncing for cpu (Jakub)

---
 include/net/page_pool/helpers.h | 35 ++++++++++++++++++++++++++++-----
 include/net/page_pool/types.h   |  3 ++-
 net/core/devmem.c               |  1 +
 net/core/page_pool.c            |  1 +
 4 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/include/net/page_pool/helpers.h b/include/net/page_pool/helpers.h
index 95af7f0b029e..e555921e5233 100644
--- a/include/net/page_pool/helpers.h
+++ b/include/net/page_pool/helpers.h
@@ -422,7 +422,21 @@ static inline dma_addr_t page_pool_get_dma_addr_netmem(netmem_ref netmem)
  */
 static inline dma_addr_t page_pool_get_dma_addr(const struct page *page)
 {
-	return page_pool_get_dma_addr_netmem(page_to_netmem((struct page *)page));
+	dma_addr_t ret = page->dma_addr;
+
+	if (PAGE_POOL_32BIT_ARCH_WITH_64BIT_DMA)
+		ret <<= PAGE_SHIFT;
+
+	return ret;
+}
+
+static inline void __page_pool_dma_sync_for_cpu(const struct page_pool *pool,
+						const dma_addr_t dma_addr,
+						u32 offset, u32 dma_sync_size)
+{
+	dma_sync_single_range_for_cpu(pool->p.dev, dma_addr,
+				      offset + pool->p.offset, dma_sync_size,
+				      page_pool_get_dma_dir(pool));
 }
 
 /**
@@ -441,10 +455,21 @@ static inline void page_pool_dma_sync_for_cpu(const struct page_pool *pool,
 					      const struct page *page,
 					      u32 offset, u32 dma_sync_size)
 {
-	dma_sync_single_range_for_cpu(pool->p.dev,
-				      page_pool_get_dma_addr(page),
-				      offset + pool->p.offset, dma_sync_size,
-				      page_pool_get_dma_dir(pool));
+	__page_pool_dma_sync_for_cpu(pool, page_pool_get_dma_addr(page), offset,
+				     dma_sync_size);
+}
+
+static inline void
+page_pool_dma_sync_netmem_for_cpu(const struct page_pool *pool,
+				  const netmem_ref netmem, u32 offset,
+				  u32 dma_sync_size)
+{
+	if (!pool->dma_sync_for_cpu)
+		return;
+
+	__page_pool_dma_sync_for_cpu(pool,
+				     page_pool_get_dma_addr_netmem(netmem),
+				     offset, dma_sync_size);
 }
 
 static inline bool page_pool_put(struct page_pool *pool)
diff --git a/include/net/page_pool/types.h b/include/net/page_pool/types.h
index bd1170e16cff..6ae003d3647c 100644
--- a/include/net/page_pool/types.h
+++ b/include/net/page_pool/types.h
@@ -164,7 +164,8 @@ struct page_pool {
 
 	bool has_init_callback:1;	/* slow::init_callback is set */
 	bool dma_map:1;			/* Perform DMA mapping */
-	bool dma_sync:1;		/* Perform DMA sync */
+	bool dma_sync:1;		/* Perform DMA sync for device */
+	bool dma_sync_for_cpu:1;	/* Perform DMA sync for cpu */
 #ifdef CONFIG_PAGE_POOL_STATS
 	bool system:1;			/* This is a global percpu pool */
 #endif
diff --git a/net/core/devmem.c b/net/core/devmem.c
index 3ebdeed2bf18..0b6ed7525b22 100644
--- a/net/core/devmem.c
+++ b/net/core/devmem.c
@@ -335,6 +335,7 @@ int mp_dmabuf_devmem_init(struct page_pool *pool)
 	 * dma_sync_for_cpu/device. Force disable dma_sync.
 	 */
 	pool->dma_sync = false;
+	pool->dma_sync_for_cpu = false;
 
 	if (pool->p.order != 0)
 		return -E2BIG;
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 060450082342..51b8264de74a 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -201,6 +201,7 @@ static int page_pool_init(struct page_pool *pool,
 	memcpy(&pool->slow, &params->slow, sizeof(pool->slow));
 
 	pool->cpuid = cpuid;
+	pool->dma_sync_for_cpu = true;
 
 	/* Validate only known flags were used */
 	if (pool->slow.flags & ~PP_FLAG_ALL)
-- 
2.47.0.338.g60cca15819-goog