netmem: use netmem_desc instead of page to access ->pp in __netmem_get_pp()

To eliminate the use of the page pool fields in struct page, the page
pool code should use netmem descriptor and APIs instead.

However, __netmem_get_pp() still accesses ->pp via struct page.  So
change it to use struct netmem_desc instead, since ->pp no longer will
be available in struct page.

While at it, add a helper, __netmem_to_nmdesc(), that can be used to
unsafely get pointer to netmem_desc backing the netmem_ref, only when
the netmem_ref is always backed by system memory.

Signed-off-by: Byungchul Park <byungchul@sk.com>
Link: https://patch.msgid.link/20250721021835.63939-3-byungchul@sk.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/include/net/netmem.h b/include/net/netmem.h
index 535cf17b913455438ee8ead04bfffa78961de631..097bc74d9555429e1e2920900412f99ea1b6c6be 100644 (file)
--- a/include/net/netmem.h
+++ b/include/net/netmem.h
@@ -247,6 +247,24 @@ static inline unsigned long netmem_pfn_trace(netmem_ref netmem)
        return page_to_pfn(netmem_to_page(netmem));
 }
 
+/**
+ * __netmem_to_nmdesc - unsafely get pointer to the &netmem_desc backing
+ * @netmem
+ * @netmem: netmem reference to convert
+ *
+ * Unsafe version that can be used only when @netmem is always backed by
+ * system memory, performs faster and generates smaller object code (no
+ * check for the LSB, no WARN). When @netmem points to IOV, provokes
+ * undefined behaviour.
+ *
+ * Return: pointer to the &netmem_desc (garbage if @netmem is not backed
+ * by system memory).
+ */
+static inline struct netmem_desc *__netmem_to_nmdesc(netmem_ref netmem)
+{
+       return (__force struct netmem_desc *)netmem;
+}
+
 /* __netmem_clear_lsb - convert netmem_ref to struct net_iov * for access to
  * common fields.
  * @netmem: netmem reference to extract as net_iov.
@@ -280,7 +298,7 @@ static inline struct net_iov *__netmem_clear_lsb(netmem_ref netmem)
  */
 static inline struct page_pool *__netmem_get_pp(netmem_ref netmem)
 {
-       return __netmem_to_page(netmem)->pp;
+       return __netmem_to_nmdesc(netmem)->pp;
 }
 
 static inline struct page_pool *netmem_get_pp(netmem_ref netmem)