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| author | Christophe Leroy <christophe.leroy@csgroup.eu> | 2021-07-05 12:00:50 +0000 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2021-08-10 23:14:55 +1000 |
| commit | c8a6d91005343dea0d53be0ff0620c66934dcd44 (patch) | |
| tree | fdd1bc5992a9ea2a377b94a6cf578ed817e7335c /arch/powerpc | |
| parent | 09ca497528dac12cbbceab8197011c875a96d053 (diff) | |
| download | lwn-c8a6d91005343dea0d53be0ff0620c66934dcd44.tar.gz lwn-c8a6d91005343dea0d53be0ff0620c66934dcd44.zip | |
powerpc/non-smp: Unconditionaly call smp_mb() on switch_mm
Commit 3ccfebedd8cf ("powerpc, membarrier: Skip memory barrier in
switch_mm()") added some logic to skip the smp_mb() in
switch_mm_irqs_off() before the call to switch_mmu_context().
However, on non SMP smp_mb() is just a compiler barrier and doing
it unconditionaly is simpler than the logic used to check whether the
barrier is needed or not.
After the patch:
00000000 <switch_mm_irqs_off>:
...
c: 7c 04 18 40 cmplw r4,r3
10: 81 24 00 24 lwz r9,36(r4)
14: 91 25 04 c8 stw r9,1224(r5)
18: 4d 82 00 20 beqlr
1c: 48 00 00 00 b 1c <switch_mm_irqs_off+0x1c>
1c: R_PPC_REL24 switch_mmu_context
Before the patch:
00000000 <switch_mm_irqs_off>:
...
c: 7c 04 18 40 cmplw r4,r3
10: 81 24 00 24 lwz r9,36(r4)
14: 91 25 04 c8 stw r9,1224(r5)
18: 4d 82 00 20 beqlr
1c: 81 24 00 28 lwz r9,40(r4)
20: 71 29 00 0a andi. r9,r9,10
24: 40 82 00 34 bne 58 <switch_mm_irqs_off+0x58>
28: 48 00 00 00 b 28 <switch_mm_irqs_off+0x28>
28: R_PPC_REL24 switch_mmu_context
...
58: 2c 03 00 00 cmpwi r3,0
5c: 41 82 ff cc beq 28 <switch_mm_irqs_off+0x28>
60: 48 00 00 00 b 60 <switch_mm_irqs_off+0x60>
60: R_PPC_REL24 switch_mmu_context
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/e9d501da0c59f60ca767b1b3ea4603fce6d02b9e.1625486440.git.christophe.leroy@csgroup.eu
Diffstat (limited to 'arch/powerpc')
| -rw-r--r-- | arch/powerpc/include/asm/membarrier.h | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/arch/powerpc/include/asm/membarrier.h b/arch/powerpc/include/asm/membarrier.h index 6e20bb5c74ea..de7f79157918 100644 --- a/arch/powerpc/include/asm/membarrier.h +++ b/arch/powerpc/include/asm/membarrier.h @@ -12,7 +12,8 @@ static inline void membarrier_arch_switch_mm(struct mm_struct *prev, * when switching from userspace to kernel is not needed after * store to rq->curr. */ - if (likely(!(atomic_read(&next->membarrier_state) & + if (IS_ENABLED(CONFIG_SMP) && + likely(!(atomic_read(&next->membarrier_state) & (MEMBARRIER_STATE_PRIVATE_EXPEDITED | MEMBARRIER_STATE_GLOBAL_EXPEDITED)) || !prev)) return; |