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authorMichael Neuling2013-02-27 04:45:52 -0600
committerBenjamin Herrenschmidt2013-03-04 23:56:28 -0600
commit6a404806dfceba9b154015705a9e647fa7749fd8 (patch)
tree773110aa64ab8777c7ca4ba56a5556a6262de7d1
parent9276dfd27897a0b29d8b5814f39a1f82f56b6b6b (diff)
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powerpc: Avoid link stack corruption in MMU on syscall entry path
Currently we use the link register to branch up high in the early MMU on syscall entry path. Unfortunately, this trashes the link stack as the address we are going to is not associated with the earlier mflr. This patch simply converts us to used the count register (volatile over syscalls anyway) instead. This is much better at predicting in this scenario and doesn't trash link stack causing a bunch of additional branch mispredicts later. Benchmarking this on POWER8 saves a bunch of cycles on Anton's null syscall benchmark here: http://ozlabs.org/~anton/junkcode/null_syscall.c Signed-off-by: Michael Neuling <mikey@neuling.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
-rw-r--r--arch/powerpc/kernel/exceptions-64s.S4
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index a8a5361fb70..87ef8f5ee5b 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -74,13 +74,13 @@ END_FTR_SECTION_IFSET(CPU_FTR_REAL_LE) \
74 mflr r10 ; \ 74 mflr r10 ; \
75 ld r12,PACAKBASE(r13) ; \ 75 ld r12,PACAKBASE(r13) ; \
76 LOAD_HANDLER(r12, system_call_entry_direct) ; \ 76 LOAD_HANDLER(r12, system_call_entry_direct) ; \
77 mtlr r12 ; \ 77 mtctr r12 ; \
78 mfspr r12,SPRN_SRR1 ; \ 78 mfspr r12,SPRN_SRR1 ; \
79 /* Re-use of r13... No spare regs to do this */ \ 79 /* Re-use of r13... No spare regs to do this */ \
80 li r13,MSR_RI ; \ 80 li r13,MSR_RI ; \
81 mtmsrd r13,1 ; \ 81 mtmsrd r13,1 ; \
82 GET_PACA(r13) ; /* get r13 back */ \ 82 GET_PACA(r13) ; /* get r13 back */ \
83 blr ; 83 bctr ;
84#else 84#else
85 /* We can branch directly */ 85 /* We can branch directly */
86#define SYSCALL_PSERIES_2_DIRECT \ 86#define SYSCALL_PSERIES_2_DIRECT \