[PATCH] cache: Make cpu_cache_invalidate_memregion() error out if there are no handlers

[Bence Csokas]

Currently, if there are no registered handlers,
cpu_cache_invalidate_memregion() returns 0. Callers are expected to check
cpu_cache_has_invalidate_memregion() and return -ENXIO themselves, instead
of calling this function. If a caller forgets to do this, they may
erroneously think the operation succeeded. This is in contrast to x86,
where cpu_cache_invalidate_memregion() itself checks if the operation is
supported, and returns -ENXIO if it is not.

Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxxxxxxxx>
Signed-off-by: Bence Csokas <bence.csokas@xxxxxxx>
---
I noticed cpu_cache_invalidate_memregion() returns 0 if there are no
registered `cache_coherency_ops_inst`s, which I find counter-intuitive.

>From what I've seen, there are no in-tree users who do not check
cpu_cache_has_invalidate_memregion(). However, IMO the better solution
would be if the function would perform this check, and not the callee.

Furthermore, arch/x86/mm/pat/set_memory.c also implements this function,
but actually does the feature check, and WARNs and returns -ENXIO if it
fails that check.

This patch that provides a low-overhead fix.
---
Changes in v1:
- Rebased to master
- Collected tags
- Link to RFC: https://patch.msgid.link/20260922-cci_enxio-v1-0-00bade212729@xxxxxxx

To: Conor Dooley <conor@xxxxxxxxxx>
To: Jonathan Cameron <jic23@xxxxxxxxxx>
To: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 lib/cache_maint.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/cache_maint.c b/lib/cache_maint.c
index 9256a9ffc34c..132d2816d6b1 100644
--- a/lib/cache_maint.c
+++ b/lib/cache_maint.c
@@ -59,12 +59,12 @@ static int cache_inval_done_one(struct cache_coherency_ops_inst *cci)
 
 static int cache_invalidate_memregion(phys_addr_t addr, size_t size)
 {
-	int ret;
 	struct cache_coherency_ops_inst *cci;
 	struct cc_inval_params params = {
 		.addr = addr,
 		.size = size,
 	};
+	int ret = -ENXIO;
 
 	guard(rwsem_read)(&cache_ops_instance_list_lock);
 	list_for_each_entry(cci, &cache_ops_instance_list, node) {
@@ -78,7 +78,7 @@ static int cache_invalidate_memregion(phys_addr_t addr, size_t size)
 			return ret;
 	}
 
-	return 0;
+	return ret;
 }
 
 struct cache_coherency_ops_inst *

---
base-commit: 551c722f40809618230001baccf219193e22fc5a
change-id: 20260921-cci_enxio-f3d31d9acec7

Best regards,
--  
Bence Csokas <bence.csokas@xxxxxxx>