From 10bcc80e9dbced128e3b4aa86e4737e5486a45d0 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Mon, 29 Jan 2018 15:20:18 -0500 Subject: membarrier/x86: Provide core serializing command There are two places where core serialization is needed by membarrier: 1) When returning from the membarrier IPI, 2) After scheduler updates curr to a thread with a different mm, before going back to user-space, since the curr->mm is used by membarrier to check whether it needs to send an IPI to that CPU. x86-32 uses IRET as return from interrupt, and both IRET and SYSEXIT to go back to user-space. The IRET instruction is core serializing, but not SYSEXIT. x86-64 uses IRET as return from interrupt, which takes care of the IPI. However, it can return to user-space through either SYSRETL (compat code), SYSRETQ, or IRET. Given that SYSRET{L,Q} is not core serializing, we rely instead on write_cr3() performed by switch_mm() to provide core serialization after changing the current mm, and deal with the special case of kthread -> uthread (temporarily keeping current mm into active_mm) by adding a sync_core() in that specific case. Use the new sync_core_before_usermode() to guarantee this. Signed-off-by: Mathieu Desnoyers Acked-by: Thomas Gleixner Acked-by: Peter Zijlstra (Intel) Cc: Andrea Parri Cc: Andrew Hunter Cc: Andy Lutomirski Cc: Avi Kivity Cc: Benjamin Herrenschmidt Cc: Boqun Feng Cc: Dave Watson Cc: David Sehr Cc: Greg Hackmann Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Maged Michael Cc: Michael Ellerman Cc: Paul E. McKenney Cc: Paul Mackerras Cc: Russell King Cc: Will Deacon Cc: linux-api@vger.kernel.org Cc: linux-arch@vger.kernel.org Link: http://lkml.kernel.org/r/20180129202020.8515-10-mathieu.desnoyers@efficios.com Signed-off-by: Ingo Molnar --- arch/x86/Kconfig | 1 + arch/x86/entry/entry_32.S | 5 +++++ arch/x86/entry/entry_64.S | 4 ++++ arch/x86/mm/tlb.c | 7 ++++--- 4 files changed, 14 insertions(+), 3 deletions(-) (limited to 'arch') diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index 31030ade4690..e095bdb9afdf 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -54,6 +54,7 @@ config X86 select ARCH_HAS_FORTIFY_SOURCE select ARCH_HAS_GCOV_PROFILE_ALL select ARCH_HAS_KCOV if X86_64 + select ARCH_HAS_MEMBARRIER_SYNC_CORE select ARCH_HAS_PMEM_API if X86_64 select ARCH_HAS_REFCOUNT select ARCH_HAS_UACCESS_FLUSHCACHE if X86_64 diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S index 2a35b1e0fb90..abee6d2b9311 100644 --- a/arch/x86/entry/entry_32.S +++ b/arch/x86/entry/entry_32.S @@ -566,6 +566,11 @@ restore_all: .Lrestore_nocheck: RESTORE_REGS 4 # skip orig_eax/error_code .Lirq_return: + /* + * ARCH_HAS_MEMBARRIER_SYNC_CORE rely on IRET core serialization + * when returning from IPI handler and when returning from + * scheduler to user-space. + */ INTERRUPT_RETURN .section .fixup, "ax" diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index a83570495162..5816858c8820 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -804,6 +804,10 @@ GLOBAL(restore_regs_and_return_to_kernel) POP_EXTRA_REGS POP_C_REGS addq $8, %rsp /* skip regs->orig_ax */ + /* + * ARCH_HAS_MEMBARRIER_SYNC_CORE rely on IRET core serialization + * when returning from IPI handler. + */ INTERRUPT_RETURN ENTRY(native_iret) diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 9fa7d2e0e15e..9b34121c8f05 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -229,9 +229,10 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, this_cpu_write(cpu_tlbstate.is_lazy, false); /* - * The membarrier system call requires a full memory barrier - * before returning to user-space, after storing to rq->curr. - * Writing to CR3 provides that full memory barrier. + * The membarrier system call requires a full memory barrier and + * core serialization before returning to user-space, after + * storing to rq->curr. Writing to CR3 provides that full + * memory barrier and core serializing instruction. */ if (real_prev == next) { VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[prev_asid].ctx_id) != -- cgit v1.2.3