xsk: add helper to get &xdp_desc's DMA and meta pointer in one go

Currently, when your driver supports XSk Tx metadata and you want to
send an XSk frame, you need to do the following:

* call external xsk_buff_raw_get_dma();
* call inline xsk_buff_get_metadata(), which calls external
  xsk_buff_raw_get_data() and then do some inline checks.

This effectively means that the following piece:

addr = pool->unaligned ? xp_unaligned_add_offset_to_addr(addr) : addr;

is done twice per frame, plus you have 2 external calls per frame, plus
this:

	meta = pool->addrs + addr - pool->tx_metadata_len;
	if (unlikely(!xsk_buff_valid_tx_metadata(meta)))

is always inlined, even if there's no meta or it's invalid.

Add xsk_buff_raw_get_ctx() (xp_raw_get_ctx() to be precise) to do that
in one go. It returns a small structure with 2 fields: DMA address,
filled unconditionally, and metadata pointer, non-NULL only if it's
present and valid. The address correction is performed only once and
you also have only 1 external call per XSk frame, which does all the
calculations and checks outside of your hotpath. You only need to
check `if (ctx.meta)` for the metadata presence.
To not copy any existing code, derive address correction and getting
virtual and DMA address into small helpers. bloat-o-meter reports no
object code changes for the existing functionality.

Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>
Link: https://patch.msgid.link/20250206182630.3914318-5-aleksander.lobakin@intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/xdp_sock_drv.h b/include/net/xdp_sock_drv.h
index 784cd34f5bba50fba0ea3d823ee12f8addb16a9d..15086dcf51d850f548ea65c7f6f764407c956772 100644 (file)
--- a/include/net/xdp_sock_drv.h
+++ b/include/net/xdp_sock_drv.h
@@ -196,6 +196,23 @@ static inline void *xsk_buff_raw_get_data(struct xsk_buff_pool *pool, u64 addr)
        return xp_raw_get_data(pool, addr);
 }
 
+/**
+ * xsk_buff_raw_get_ctx - get &xdp_desc context
+ * @pool: XSk buff pool desc address belongs to
+ * @addr: desc address (from userspace)
+ *
+ * Wrapper for xp_raw_get_ctx() to be used in drivers, see its kdoc for
+ * details.
+ *
+ * Return: new &xdp_desc_ctx struct containing desc's DMA address and metadata
+ * pointer, if it is present and valid (initialized to %NULL otherwise).
+ */
+static inline struct xdp_desc_ctx
+xsk_buff_raw_get_ctx(const struct xsk_buff_pool *pool, u64 addr)
+{
+       return xp_raw_get_ctx(pool, addr);
+}
+
 #define XDP_TXMD_FLAGS_VALID ( \
                XDP_TXMD_FLAGS_TIMESTAMP | \
                XDP_TXMD_FLAGS_CHECKSUM | \
@@ -207,20 +224,27 @@ xsk_buff_valid_tx_metadata(const struct xsk_tx_metadata *meta)
        return !(meta->flags & ~XDP_TXMD_FLAGS_VALID);
 }
 
-static inline struct xsk_tx_metadata *xsk_buff_get_metadata(struct xsk_buff_pool *pool, u64 addr)
+static inline struct xsk_tx_metadata *
+__xsk_buff_get_metadata(const struct xsk_buff_pool *pool, void *data)
 {
        struct xsk_tx_metadata *meta;
 
        if (!pool->tx_metadata_len)
                return NULL;
 
-       meta = xp_raw_get_data(pool, addr) - pool->tx_metadata_len;
+       meta = data - pool->tx_metadata_len;
        if (unlikely(!xsk_buff_valid_tx_metadata(meta)))
                return NULL; /* no way to signal the error to the user */
 
        return meta;
 }
 
+static inline struct xsk_tx_metadata *
+xsk_buff_get_metadata(struct xsk_buff_pool *pool, u64 addr)
+{
+       return __xsk_buff_get_metadata(pool, xp_raw_get_data(pool, addr));
+}
+
 static inline void xsk_buff_dma_sync_for_cpu(struct xdp_buff *xdp)
 {
        struct xdp_buff_xsk *xskb = container_of(xdp, struct xdp_buff_xsk, xdp);
@@ -388,12 +412,25 @@ static inline void *xsk_buff_raw_get_data(struct xsk_buff_pool *pool, u64 addr)
        return NULL;
 }
 
+static inline struct xdp_desc_ctx
+xsk_buff_raw_get_ctx(const struct xsk_buff_pool *pool, u64 addr)
+{
+       return (struct xdp_desc_ctx){ };
+}
+
 static inline bool xsk_buff_valid_tx_metadata(struct xsk_tx_metadata *meta)
 {
        return false;
 }
 
-static inline struct xsk_tx_metadata *xsk_buff_get_metadata(struct xsk_buff_pool *pool, u64 addr)
+static inline struct xsk_tx_metadata *
+__xsk_buff_get_metadata(const struct xsk_buff_pool *pool, void *data)
+{
+       return NULL;
+}
+
+static inline struct xsk_tx_metadata *
+xsk_buff_get_metadata(struct xsk_buff_pool *pool, u64 addr)
 {
        return NULL;
 }

diff --git a/include/net/xsk_buff_pool.h b/include/net/xsk_buff_pool.h
index 50779406bc2d91c57c5b55638c2e2e31b1d4edce..1dcd4d71468a5ffc64e4e5aeca3e0127a6dd72d2 100644 (file)
--- a/include/net/xsk_buff_pool.h
+++ b/include/net/xsk_buff_pool.h
@@ -141,6 +141,14 @@ u32 xp_alloc_batch(struct xsk_buff_pool *pool, struct xdp_buff **xdp, u32 max);
 bool xp_can_alloc(struct xsk_buff_pool *pool, u32 count);
 void *xp_raw_get_data(struct xsk_buff_pool *pool, u64 addr);
 dma_addr_t xp_raw_get_dma(struct xsk_buff_pool *pool, u64 addr);
+
+struct xdp_desc_ctx {
+       dma_addr_t dma;
+       struct xsk_tx_metadata *meta;
+};
+
+struct xdp_desc_ctx xp_raw_get_ctx(const struct xsk_buff_pool *pool, u64 addr);
+
 static inline dma_addr_t xp_get_dma(struct xdp_buff_xsk *xskb)
 {
        return xskb->dma;

diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
index 1f7975b4965794f5de345cacccbecec0b03c5634..c263fb7a68dc35e737c030d62cd25aadf552766b 100644 (file)
--- a/net/xdp/xsk_buff_pool.c
+++ b/net/xdp/xsk_buff_pool.c
@@ -699,18 +699,56 @@ void xp_free(struct xdp_buff_xsk *xskb)
 }
 EXPORT_SYMBOL(xp_free);
 
-void *xp_raw_get_data(struct xsk_buff_pool *pool, u64 addr)
+static u64 __xp_raw_get_addr(const struct xsk_buff_pool *pool, u64 addr)
+{
+       return pool->unaligned ? xp_unaligned_add_offset_to_addr(addr) : addr;
+}
+
+static void *__xp_raw_get_data(const struct xsk_buff_pool *pool, u64 addr)
 {
-       addr = pool->unaligned ? xp_unaligned_add_offset_to_addr(addr) : addr;
        return pool->addrs + addr;
 }
+
+void *xp_raw_get_data(struct xsk_buff_pool *pool, u64 addr)
+{
+       return __xp_raw_get_data(pool, __xp_raw_get_addr(pool, addr));
+}
 EXPORT_SYMBOL(xp_raw_get_data);
 
-dma_addr_t xp_raw_get_dma(struct xsk_buff_pool *pool, u64 addr)
+static dma_addr_t __xp_raw_get_dma(const struct xsk_buff_pool *pool, u64 addr)
 {
-       addr = pool->unaligned ? xp_unaligned_add_offset_to_addr(addr) : addr;
        return (pool->dma_pages[addr >> PAGE_SHIFT] &
                ~XSK_NEXT_PG_CONTIG_MASK) +
                (addr & ~PAGE_MASK);
 }
+
+dma_addr_t xp_raw_get_dma(struct xsk_buff_pool *pool, u64 addr)
+{
+       return __xp_raw_get_dma(pool, __xp_raw_get_addr(pool, addr));
+}
 EXPORT_SYMBOL(xp_raw_get_dma);
+
+/**
+ * xp_raw_get_ctx - get &xdp_desc context
+ * @pool: XSk buff pool desc address belongs to
+ * @addr: desc address (from userspace)
+ *
+ * Helper for getting desc's DMA address and metadata pointer, if present.
+ * Saves one call on hotpath, double calculation of the actual address,
+ * and inline checks for metadata presence and sanity.
+ *
+ * Return: new &xdp_desc_ctx struct containing desc's DMA address and metadata
+ * pointer, if it is present and valid (initialized to %NULL otherwise).
+ */
+struct xdp_desc_ctx xp_raw_get_ctx(const struct xsk_buff_pool *pool, u64 addr)
+{
+       struct xdp_desc_ctx ret;
+
+       addr = __xp_raw_get_addr(pool, addr);
+
+       ret.dma = __xp_raw_get_dma(pool, addr);
+       ret.meta = __xsk_buff_get_metadata(pool, __xp_raw_get_data(pool, addr));
+
+       return ret;
+}
+EXPORT_SYMBOL(xp_raw_get_ctx);