[PATCH v5 13/18] powerpc/e500: Don't pre-check write access on data TLB error

Christophe Leroy
2024-06-10T05:56:01Z

Don't pre-check write access on read-only pages on data TLB error.

Load the TLB anyway and take a DSI exception when it happens. This
avoids reading SPRN_ESR at every data TLB error exception.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
---
v5: New
---
arch/powerpc/kernel/head_85xx.S | 15 ---------------
1 file changed, 15 deletions(-)

diff --git a/arch/powerpc/kernel/head_85xx.S b/arch/powerpc/kernel/head_85xx.S
index a305244afc9f..282e49c51deb 100644
--- a/arch/powerpc/kernel/head_85xx.S
+++ b/arch/powerpc/kernel/head_85xx.S
@@ -472,27 +472,12 @@ END_BTB_FLUSH_SECTION
#endif

4:
- /* Mask of required permission bits. Note that while we
- * do copy ESR:ST to _PAGE_WRITE position as trying to write
- * to an RO page is pretty common, we don't do it with
- * _PAGE_DIRTY. We could do it, but it's a fairly rare
- * event so I'd rather take the overhead when it happens
- * rather than adding an instruction here. We should measure
- * whether the whole thing is worth it in the first place
- * as we could avoid loading SPRN_ESR completely in the first
- * place...
- *
- * TODO: Is it worth doing that mfspr & rlwimi in the first
- * place or can we save a couple of instructions here ?
- */
- mfspr r12,SPRN_ESR
#ifdef CONFIG_PTE_64BIT
li r13,_PAGE_PRESENT|_PAGE_BAP_SR
oris r13,r13,_PAGE_ACCESSED@h
#else
li r13,_PAGE_PRESENT|_PAGE_READ|_PAGE_ACCESSED
#endif
- rlwimi r13,r12,11,29,29

FIND_PTE
andc. r13,r13,r11 /* Check permission */
--
2.44.0