To enable/disable kernel access to user space, the 8xx has to modify the properties of access group 1. This is done by writing predefined values into SPRN_Mx_AP registers.
As of today, a __put_user() gives: 00000d64 <my_test>: d64: 3d 20 4f ff lis r9,20479 d68: 61 29 ff ff ori r9,r9,65535 d6c: 7d 3a c3 a6 mtspr 794,r9 d70: 39 20 00 00 li r9,0 d74: 90 83 00 00 stw r4,0(r3) d78: 3d 20 6f ff lis r9,28671 d7c: 61 29 ff ff ori r9,r9,65535 d80: 7d 3a c3 a6 mtspr 794,r9 d84: 4e 80 00 20 blr Because only groups 0 and 1 are used, the definition of groups 2 to 15 doesn't matter. By setting unused bits to 0 instead on 1, one instruction is removed for each lock and unlock action: 00000d5c <my_test>: d5c: 3d 20 40 00 lis r9,16384 d60: 7d 3a c3 a6 mtspr 794,r9 d64: 39 20 00 00 li r9,0 d68: 90 83 00 00 stw r4,0(r3) d6c: 3d 20 60 00 lis r9,24576 d70: 7d 3a c3 a6 mtspr 794,r9 d74: 4e 80 00 20 blr Signed-off-by: Christophe Leroy <christophe.le...@c-s.fr> --- arch/powerpc/include/asm/nohash/32/mmu-8xx.h | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/arch/powerpc/include/asm/nohash/32/mmu-8xx.h b/arch/powerpc/include/asm/nohash/32/mmu-8xx.h index 76af5b0cb16e..6aa3464a88ed 100644 --- a/arch/powerpc/include/asm/nohash/32/mmu-8xx.h +++ b/arch/powerpc/include/asm/nohash/32/mmu-8xx.h @@ -37,16 +37,16 @@ * Therefore, we define 2 APG groups. lsb is _PMD_USER * 0 => Kernel => 01 (all accesses performed according to page definition) * 1 => User => 00 (all accesses performed as supervisor iaw page definition) - * 2-16 => NA => 11 (all accesses performed as user iaw page definition) + * 2-15 => Not Used */ -#define MI_APG_INIT 0x4fffffff +#define MI_APG_INIT 0x40000000 /* * 0 => Kernel => 01 (all accesses performed according to page definition) * 1 => User => 10 (all accesses performed according to swaped page definition) - * 2-16 => NA => 11 (all accesses performed as user iaw page definition) + * 2-15 => Not Used */ -#define MI_APG_KUEP 0x6fffffff +#define MI_APG_KUEP 0x60000000 /* The effective page number register. When read, contains the information * about the last instruction TLB miss. When MI_RPN is written, bits in @@ -117,16 +117,16 @@ * Therefore, we define 2 APG groups. lsb is _PMD_USER * 0 => Kernel => 01 (all accesses performed according to page definition) * 1 => User => 00 (all accesses performed as supervisor iaw page definition) - * 2-16 => NA => 11 (all accesses performed as user iaw page definition) + * 2-15 => Not Used */ -#define MD_APG_INIT 0x4fffffff +#define MD_APG_INIT 0x40000000 /* * 0 => No user => 01 (all accesses performed according to page definition) * 1 => User => 10 (all accesses performed according to swaped page definition) - * 2-16 => NA => 11 (all accesses performed as user iaw page definition) + * 2-15 => Not Used */ -#define MD_APG_KUAP 0x6fffffff +#define MD_APG_KUAP 0x60000000 /* The effective page number register. When read, contains the information * about the last instruction TLB miss. When MD_RPN is written, bits in -- 2.25.0
