From: Andy Lutomirski <luto@kernel.org> To: x86@kernel.org Cc: Dave Hansen <dave.hansen@intel.com>, LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>, Andy Lutomirski <luto@kernel.org>, Michael Ellerman <mpe@ellerman.id.au>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>, linuxppc-dev@lists.ozlabs.org, Nicholas Piggin <npiggin@gmail.com>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Peter Zijlstra <peterz@infradead.org> Subject: [PATCH 6/8] powerpc/membarrier: Remove special barrier on mm switch Date: Tue, 15 Jun 2021 20:21:11 -0700 [thread overview] Message-ID: <d9034f951329830b766feb08099c15b714e08e8f.1623813516.git.luto@kernel.org> (raw) In-Reply-To: <cover.1623813516.git.luto@kernel.org> powerpc did the following on some, but not all, paths through switch_mm_irqs_off(): /* * Only need the full barrier when switching between processes. * Barrier when switching from kernel to userspace is not * required here, given that it is implied by mmdrop(). Barrier * when switching from userspace to kernel is not needed after * store to rq->curr. */ if (likely(!(atomic_read(&next->membarrier_state) & (MEMBARRIER_STATE_PRIVATE_EXPEDITED | MEMBARRIER_STATE_GLOBAL_EXPEDITED)) || !prev)) return; This is puzzling: if !prev, then one might expect that we are switching from kernel to user, not user to kernel, which is inconsistent with the comment. But this is all nonsense, because the one and only caller would never have prev == NULL and would, in fact, OOPS if prev == NULL. In any event, this code is unnecessary, since the new generic membarrier_finish_switch_mm() provides the same barrier without arch help. Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: linuxppc-dev@lists.ozlabs.org Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Andy Lutomirski <luto@kernel.org> --- arch/powerpc/include/asm/membarrier.h | 27 --------------------------- arch/powerpc/mm/mmu_context.c | 2 -- 2 files changed, 29 deletions(-) delete mode 100644 arch/powerpc/include/asm/membarrier.h diff --git a/arch/powerpc/include/asm/membarrier.h b/arch/powerpc/include/asm/membarrier.h deleted file mode 100644 index 6e20bb5c74ea..000000000000 --- a/arch/powerpc/include/asm/membarrier.h +++ /dev/null @@ -1,27 +0,0 @@ -#ifndef _ASM_POWERPC_MEMBARRIER_H -#define _ASM_POWERPC_MEMBARRIER_H - -static inline void membarrier_arch_switch_mm(struct mm_struct *prev, - struct mm_struct *next, - struct task_struct *tsk) -{ - /* - * Only need the full barrier when switching between processes. - * Barrier when switching from kernel to userspace is not - * required here, given that it is implied by mmdrop(). Barrier - * when switching from userspace to kernel is not needed after - * store to rq->curr. - */ - if (likely(!(atomic_read(&next->membarrier_state) & - (MEMBARRIER_STATE_PRIVATE_EXPEDITED | - MEMBARRIER_STATE_GLOBAL_EXPEDITED)) || !prev)) - return; - - /* - * The membarrier system call requires a full memory barrier - * after storing to rq->curr, before going back to user-space. - */ - smp_mb(); -} - -#endif /* _ASM_POWERPC_MEMBARRIER_H */ diff --git a/arch/powerpc/mm/mmu_context.c b/arch/powerpc/mm/mmu_context.c index a857af401738..8daa95b3162b 100644 --- a/arch/powerpc/mm/mmu_context.c +++ b/arch/powerpc/mm/mmu_context.c @@ -85,8 +85,6 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, if (new_on_cpu) radix_kvm_prefetch_workaround(next); - else - membarrier_arch_switch_mm(prev, next, tsk); /* * The actual HW switching method differs between the various -- 2.31.1
WARNING: multiple messages have this Message-ID (diff)
From: Andy Lutomirski <luto@kernel.org> To: x86@kernel.org Cc: linux-mm@kvack.org, Peter Zijlstra <peterz@infradead.org>, LKML <linux-kernel@vger.kernel.org>, Nicholas Piggin <npiggin@gmail.com>, Dave Hansen <dave.hansen@intel.com>, Paul Mackerras <paulus@samba.org>, Andy Lutomirski <luto@kernel.org>, Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, Andrew Morton <akpm@linux-foundation.org>, linuxppc-dev@lists.ozlabs.org Subject: [PATCH 6/8] powerpc/membarrier: Remove special barrier on mm switch Date: Tue, 15 Jun 2021 20:21:11 -0700 [thread overview] Message-ID: <d9034f951329830b766feb08099c15b714e08e8f.1623813516.git.luto@kernel.org> (raw) In-Reply-To: <cover.1623813516.git.luto@kernel.org> powerpc did the following on some, but not all, paths through switch_mm_irqs_off(): /* * Only need the full barrier when switching between processes. * Barrier when switching from kernel to userspace is not * required here, given that it is implied by mmdrop(). Barrier * when switching from userspace to kernel is not needed after * store to rq->curr. */ if (likely(!(atomic_read(&next->membarrier_state) & (MEMBARRIER_STATE_PRIVATE_EXPEDITED | MEMBARRIER_STATE_GLOBAL_EXPEDITED)) || !prev)) return; This is puzzling: if !prev, then one might expect that we are switching from kernel to user, not user to kernel, which is inconsistent with the comment. But this is all nonsense, because the one and only caller would never have prev == NULL and would, in fact, OOPS if prev == NULL. In any event, this code is unnecessary, since the new generic membarrier_finish_switch_mm() provides the same barrier without arch help. Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Cc: Paul Mackerras <paulus@samba.org> Cc: linuxppc-dev@lists.ozlabs.org Cc: Nicholas Piggin <npiggin@gmail.com> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Andy Lutomirski <luto@kernel.org> --- arch/powerpc/include/asm/membarrier.h | 27 --------------------------- arch/powerpc/mm/mmu_context.c | 2 -- 2 files changed, 29 deletions(-) delete mode 100644 arch/powerpc/include/asm/membarrier.h diff --git a/arch/powerpc/include/asm/membarrier.h b/arch/powerpc/include/asm/membarrier.h deleted file mode 100644 index 6e20bb5c74ea..000000000000 --- a/arch/powerpc/include/asm/membarrier.h +++ /dev/null @@ -1,27 +0,0 @@ -#ifndef _ASM_POWERPC_MEMBARRIER_H -#define _ASM_POWERPC_MEMBARRIER_H - -static inline void membarrier_arch_switch_mm(struct mm_struct *prev, - struct mm_struct *next, - struct task_struct *tsk) -{ - /* - * Only need the full barrier when switching between processes. - * Barrier when switching from kernel to userspace is not - * required here, given that it is implied by mmdrop(). Barrier - * when switching from userspace to kernel is not needed after - * store to rq->curr. - */ - if (likely(!(atomic_read(&next->membarrier_state) & - (MEMBARRIER_STATE_PRIVATE_EXPEDITED | - MEMBARRIER_STATE_GLOBAL_EXPEDITED)) || !prev)) - return; - - /* - * The membarrier system call requires a full memory barrier - * after storing to rq->curr, before going back to user-space. - */ - smp_mb(); -} - -#endif /* _ASM_POWERPC_MEMBARRIER_H */ diff --git a/arch/powerpc/mm/mmu_context.c b/arch/powerpc/mm/mmu_context.c index a857af401738..8daa95b3162b 100644 --- a/arch/powerpc/mm/mmu_context.c +++ b/arch/powerpc/mm/mmu_context.c @@ -85,8 +85,6 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, if (new_on_cpu) radix_kvm_prefetch_workaround(next); - else - membarrier_arch_switch_mm(prev, next, tsk); /* * The actual HW switching method differs between the various -- 2.31.1
next prev parent reply other threads:[~2021-06-16 3:21 UTC|newest] Thread overview: 165+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-16 3:21 [PATCH 0/8] membarrier cleanups Andy Lutomirski 2021-06-16 3:21 ` [PATCH 1/8] membarrier: Document why membarrier() works Andy Lutomirski 2021-06-16 4:00 ` Nicholas Piggin 2021-06-16 7:30 ` Peter Zijlstra 2021-06-17 23:45 ` Andy Lutomirski 2021-06-16 3:21 ` [PATCH 2/8] x86/mm: Handle unlazying membarrier core sync in the arch code Andy Lutomirski 2021-06-16 4:25 ` Nicholas Piggin 2021-06-16 18:31 ` Andy Lutomirski 2021-06-16 17:49 ` Mathieu Desnoyers 2021-06-16 17:49 ` Mathieu Desnoyers 2021-06-16 18:31 ` Andy Lutomirski 2021-06-16 3:21 ` [PATCH 3/8] membarrier: Remove membarrier_arch_switch_mm() prototype in core code Andy Lutomirski 2021-06-16 4:26 ` Nicholas Piggin 2021-06-16 17:52 ` Mathieu Desnoyers 2021-06-16 17:52 ` Mathieu Desnoyers 2021-06-16 3:21 ` [PATCH 4/8] membarrier: Make the post-switch-mm barrier explicit Andy Lutomirski 2021-06-16 4:19 ` Nicholas Piggin 2021-06-16 7:35 ` Peter Zijlstra 2021-06-16 18:41 ` Andy Lutomirski 2021-06-17 1:37 ` Nicholas Piggin 2021-06-17 2:57 ` Andy Lutomirski 2021-06-17 5:32 ` Andy Lutomirski 2021-06-17 6:51 ` Nicholas Piggin 2021-06-17 23:49 ` Andy Lutomirski 2021-06-19 2:53 ` Nicholas Piggin 2021-06-19 3:20 ` Andy Lutomirski 2021-06-19 4:27 ` Nicholas Piggin 2021-06-17 9:08 ` [RFC][PATCH] sched: Use lightweight hazard pointers to grab lazy mms Peter Zijlstra 2021-06-17 9:10 ` Peter Zijlstra 2021-06-17 10:00 ` Nicholas Piggin 2021-06-17 9:13 ` Peter Zijlstra 2021-06-17 14:06 ` Andy Lutomirski 2021-06-17 9:28 ` Peter Zijlstra 2021-06-17 14:03 ` Andy Lutomirski 2021-06-17 14:10 ` Andy Lutomirski 2021-06-17 15:45 ` Peter Zijlstra 2021-06-18 3:29 ` Paul E. McKenney 2021-06-18 5:04 ` Andy Lutomirski 2021-06-17 15:02 ` [PATCH 4/8] membarrier: Make the post-switch-mm barrier explicit Paul E. McKenney 2021-06-18 0:06 ` Andy Lutomirski 2021-06-18 3:35 ` Paul E. McKenney 2021-06-17 8:45 ` Peter Zijlstra 2021-06-16 3:21 ` [PATCH 5/8] membarrier, kthread: Use _ONCE accessors for task->mm Andy Lutomirski 2021-06-16 4:28 ` Nicholas Piggin 2021-06-16 18:08 ` Mathieu Desnoyers 2021-06-16 18:08 ` Mathieu Desnoyers 2021-06-16 18:45 ` Andy Lutomirski 2021-06-16 3:21 ` Andy Lutomirski [this message] 2021-06-16 3:21 ` [PATCH 6/8] powerpc/membarrier: Remove special barrier on mm switch Andy Lutomirski 2021-06-16 4:36 ` Nicholas Piggin 2021-06-16 4:36 ` Nicholas Piggin 2021-06-16 3:21 ` [PATCH 7/8] membarrier: Remove arm (32) support for SYNC_CORE Andy Lutomirski 2021-06-16 3:21 ` Andy Lutomirski 2021-06-16 9:28 ` Russell King (Oracle) 2021-06-16 9:28 ` Russell King (Oracle) 2021-06-16 10:16 ` Peter Zijlstra 2021-06-16 10:16 ` Peter Zijlstra 2021-06-16 10:20 ` Peter Zijlstra 2021-06-16 10:20 ` Peter Zijlstra 2021-06-16 10:34 ` Russell King (Oracle) 2021-06-16 10:34 ` Russell King (Oracle) 2021-06-16 11:10 ` Peter Zijlstra 2021-06-16 11:10 ` Peter Zijlstra 2021-06-16 13:22 ` Russell King (Oracle) 2021-06-16 13:22 ` Russell King (Oracle) 2021-06-16 15:04 ` Catalin Marinas 2021-06-16 15:04 ` Catalin Marinas 2021-06-16 15:23 ` Russell King (Oracle) 2021-06-16 15:23 ` Russell King (Oracle) 2021-06-16 15:45 ` Catalin Marinas 2021-06-16 15:45 ` Catalin Marinas 2021-06-16 16:00 ` Catalin Marinas 2021-06-16 16:00 ` Catalin Marinas 2021-06-16 16:27 ` Russell King (Oracle) 2021-06-16 16:27 ` Russell King (Oracle) 2021-06-17 8:55 ` Krzysztof Hałasa 2021-06-17 8:55 ` Krzysztof Hałasa 2021-06-17 8:55 ` Krzysztof Hałasa 2021-06-18 12:54 ` Linus Walleij 2021-06-18 12:54 ` Linus Walleij 2021-06-18 12:54 ` Linus Walleij 2021-06-18 13:19 ` Russell King (Oracle) 2021-06-18 13:19 ` Russell King (Oracle) 2021-06-18 13:36 ` Arnd Bergmann 2021-06-18 13:36 ` Arnd Bergmann 2021-06-18 13:36 ` Arnd Bergmann 2021-06-17 10:40 ` Mark Rutland 2021-06-17 10:40 ` Mark Rutland 2021-06-17 11:23 ` Russell King (Oracle) 2021-06-17 11:23 ` Russell King (Oracle) 2021-06-17 11:33 ` Mark Rutland 2021-06-17 11:33 ` Mark Rutland 2021-06-17 13:41 ` Andy Lutomirski 2021-06-17 13:41 ` Andy Lutomirski 2021-06-17 13:51 ` Mark Rutland 2021-06-17 13:51 ` Mark Rutland 2021-06-17 14:00 ` Andy Lutomirski 2021-06-17 14:00 ` Andy Lutomirski 2021-06-17 14:20 ` Mark Rutland 2021-06-17 14:20 ` Mark Rutland 2021-06-17 15:01 ` Peter Zijlstra 2021-06-17 15:01 ` Peter Zijlstra 2021-06-17 15:13 ` Peter Zijlstra 2021-06-17 15:13 ` Peter Zijlstra 2021-06-17 14:16 ` Mathieu Desnoyers 2021-06-17 14:16 ` Mathieu Desnoyers 2021-06-17 14:05 ` Peter Zijlstra 2021-06-17 14:05 ` Peter Zijlstra 2021-06-18 0:07 ` Andy Lutomirski 2021-06-18 0:07 ` Andy Lutomirski 2021-06-16 3:21 ` [PATCH 8/8] membarrier: Rewrite sync_core_before_usermode() and improve documentation Andy Lutomirski 2021-06-16 3:21 ` Andy Lutomirski 2021-06-16 3:21 ` Andy Lutomirski 2021-06-16 4:45 ` Nicholas Piggin 2021-06-16 4:45 ` Nicholas Piggin 2021-06-16 4:45 ` Nicholas Piggin 2021-06-16 18:52 ` Andy Lutomirski 2021-06-16 18:52 ` Andy Lutomirski 2021-06-16 18:52 ` Andy Lutomirski 2021-06-16 23:48 ` Andy Lutomirski 2021-06-16 23:48 ` Andy Lutomirski 2021-06-16 23:48 ` Andy Lutomirski 2021-06-18 15:27 ` Christophe Leroy 2021-06-18 15:27 ` Christophe Leroy 2021-06-18 15:27 ` Christophe Leroy 2021-06-16 10:20 ` Will Deacon 2021-06-16 10:20 ` Will Deacon 2021-06-16 10:20 ` Will Deacon 2021-06-16 23:58 ` Andy Lutomirski 2021-06-16 23:58 ` Andy Lutomirski 2021-06-16 23:58 ` Andy Lutomirski 2021-06-17 14:47 ` Mathieu Desnoyers 2021-06-17 14:47 ` Mathieu Desnoyers 2021-06-17 14:47 ` Mathieu Desnoyers 2021-06-17 14:47 ` Mathieu Desnoyers 2021-06-18 0:12 ` Andy Lutomirski 2021-06-18 0:12 ` Andy Lutomirski 2021-06-18 0:12 ` Andy Lutomirski 2021-06-18 16:31 ` Mathieu Desnoyers 2021-06-18 16:31 ` Mathieu Desnoyers 2021-06-18 16:31 ` Mathieu Desnoyers 2021-06-18 16:31 ` Mathieu Desnoyers 2021-06-18 19:58 ` Andy Lutomirski 2021-06-18 19:58 ` Andy Lutomirski 2021-06-18 19:58 ` Andy Lutomirski 2021-06-18 20:09 ` Mathieu Desnoyers 2021-06-18 20:09 ` Mathieu Desnoyers 2021-06-18 20:09 ` Mathieu Desnoyers 2021-06-18 20:09 ` Mathieu Desnoyers 2021-06-19 6:02 ` Nicholas Piggin 2021-06-19 6:02 ` Nicholas Piggin 2021-06-19 6:02 ` Nicholas Piggin 2021-06-19 15:50 ` Andy Lutomirski 2021-06-19 15:50 ` Andy Lutomirski 2021-06-19 15:50 ` Andy Lutomirski 2021-06-20 2:10 ` Nicholas Piggin 2021-06-20 2:10 ` Nicholas Piggin 2021-06-20 2:10 ` Nicholas Piggin 2021-06-17 15:16 ` Mathieu Desnoyers 2021-06-17 15:16 ` Mathieu Desnoyers 2021-06-17 15:16 ` Mathieu Desnoyers 2021-06-17 15:16 ` Mathieu Desnoyers 2021-06-18 0:13 ` Andy Lutomirski 2021-06-18 0:13 ` Andy Lutomirski 2021-06-18 0:13 ` Andy Lutomirski
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