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

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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>
This commit is contained in:
Christophe Leroy 2024-07-02 15:51:30 +02:00 committed by Andrew Morton
parent 84319905ca
commit 276d5affbb
1 changed files with 0 additions and 15 deletions
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15
arch/powerpc/kernel/head_85xx.S
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@ -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 */