lib/scatterlist: Add SG_MITER_LOCAL and use it

JIRA: https://issues.redhat.com/browse/RHEL-116573

Upstream Status: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

commit fc8d5bb
Author: Herbert Xu <herbert@gondor.apana.org.au>
Date:   Thu Mar 13 13:14:53 2025 +0800

    lib/scatterlist: Add SG_MITER_LOCAL and use it

    Add kmap_local support to the scatterlist iterator.  Use it for
    all the helper functions in lib/scatterlist.

    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Signed-off-by: Eder Zulian <ezulian@redhat.com>

Author: efzrh

include/linux/scatterlist.h

@@ -692,6 +692,7 @@ sg_page_iter_dma_address(struct sg_dma_page_iter *dma_iter)
 #define SG_MITER_ATOMIC		(1 << 0)	 /* use kmap_atomic */
 #define SG_MITER_TO_SG		(1 << 1)	/* flush back to phys on unmap */
 #define SG_MITER_FROM_SG	(1 << 2)	/* nop */
+#define SG_MITER_LOCAL		(1 << 3)	 /* use kmap_local */
 
 struct sg_mapping_iter {
 	/* the following three fields can be accessed directly */

lib/scatterlist.c

@@ -856,7 +856,7 @@ EXPORT_SYMBOL(sg_miter_skip);
  *   @miter->addr and @miter->length point to the current mapping.
  *
  * Context:
- *   May sleep if !SG_MITER_ATOMIC.
+ *   May sleep if !SG_MITER_ATOMIC && !SG_MITER_LOCAL.
  *
  * Returns:
  *   true if @miter contains the next mapping.  false if end of sg
@@ -878,6 +878,8 @@ bool sg_miter_next(struct sg_mapping_iter *miter)
 
 	if (miter->__flags & SG_MITER_ATOMIC)
 		miter->addr = kmap_atomic(miter->page) + miter->__offset;
+	else if (miter->__flags & SG_MITER_LOCAL)
+		miter->addr = kmap_local_page(miter->page) + miter->__offset;
 	else
 		miter->addr = kmap(miter->page) + miter->__offset;
 
@@ -913,7 +915,9 @@ void sg_miter_stop(struct sg_mapping_iter *miter)
 		if (miter->__flags & SG_MITER_ATOMIC) {
 			WARN_ON_ONCE(!pagefault_disabled());
 			kunmap_atomic(miter->addr);
-		} else
+		} else if (miter->__flags & SG_MITER_LOCAL)
+			kunmap_local(miter->addr);
+		else
 			kunmap(miter->page);
 
 		miter->page = NULL;
@@ -942,7 +946,7 @@ size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, void *buf,
 {
 	unsigned int offset = 0;
 	struct sg_mapping_iter miter;
-	unsigned int sg_flags = SG_MITER_ATOMIC;
+	unsigned int sg_flags = SG_MITER_LOCAL;
 
 	if (to_buffer)
 		sg_flags |= SG_MITER_FROM_SG;
@@ -1057,7 +1061,7 @@ size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents,
 {
 	unsigned int offset = 0;
 	struct sg_mapping_iter miter;
-	unsigned int sg_flags = SG_MITER_ATOMIC | SG_MITER_TO_SG;
+	unsigned int sg_flags = SG_MITER_LOCAL | SG_MITER_TO_SG;
 
 	sg_miter_start(&miter, sgl, nents, sg_flags);