efi: capsule: use atomic kmap for transient sglist mappings

Don't use the heavy-weight kmap() API to create short-lived mappings
of the scatter-gather list entries that are released as soon as the
entries are written. Instead, use kmap_atomic(), which is more suited
to this purpose.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/capsule.c

@@ -244,7 +244,7 @@ int efi_capsule_update(efi_capsule_header_t *capsule, phys_addr_t *pages)
 	for (i = 0; i < sg_count; i++) {
 		efi_capsule_block_desc_t *sglist;
 
-		sglist = kmap(sg_pages[i]);
+		sglist = kmap_atomic(sg_pages[i]);
 
 		for (j = 0; j < SGLIST_PER_PAGE && count > 0; j++) {
 			u64 sz = min_t(u64, imagesize,
@@ -265,7 +265,7 @@ int efi_capsule_update(efi_capsule_header_t *capsule, phys_addr_t *pages)
 		else
 			sglist[j].data = page_to_phys(sg_pages[i + 1]);
 
-		kunmap(sg_pages[i]);
+		kunmap_atomic(sglist);
 	}
 
 	mutex_lock(&capsule_mutex);