powerpc/e500: don't pre-check write access on data TLB error

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.

Link: https://lkml.kernel.org/r/8525518e1657d6032b7e980c1888102828d66950.1719928057.git.christophe.leroy@csgroup.eu
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/arch/powerpc/kernel/head_85xx.S b/arch/powerpc/kernel/head_85xx.S
index a305244afc9f82bdb2241a4daca8af68ec146744..282e49c51deb06949f2067c0df317a98fc195c71 100644 (file)
--- 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 */