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From: Nadav Amit <nadav.amit@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Will Deacon <will@kernel.org>, Yu Zhao <yuzhao@google.com>,
	Nick Piggin <npiggin@gmail.com>, X86 ML <x86@kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC 01/20] mm/tlb: fix fullmm semantics
Date: Tue, 2 Feb 2021 13:35:38 -0800	[thread overview]
Message-ID: <5E9B0429-7E72-4E86-B91B-4718C4134B0F@gmail.com> (raw)
In-Reply-To: <YBkwyEL2FKxlsgZ5@hirez.programming.kicks-ass.net>

> On Feb 2, 2021, at 3:00 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> 
> On Tue, Feb 02, 2021 at 01:32:36AM -0800, Nadav Amit wrote:
>>> On Feb 1, 2021, at 3:36 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>>> 
>>> 
>>> https://lkml.kernel.org/r/20210127235347.1402-1-will@kernel.org
>> 
>> I have seen this series, and applied my patches on it.
>> 
>> Despite Will’s patches, there were still inconsistencies between fullmm
>> and need_flush_all.
>> 
>> Am I missing something?
> 
> I wasn't aware you were on top. I'll look again.

Looking on arm64’s tlb_flush() makes me think that there is currently a bug
that this patch fixes. Arm64’s tlb_flush() does:

       /*
        * If we're tearing down the address space then we only care about
        * invalidating the walk-cache, since the ASID allocator won't
        * reallocate our ASID without invalidating the entire TLB.
        */
       if (tlb->fullmm) {
               if (!last_level)
                       flush_tlb_mm(tlb->mm);
               return;
       } 

But currently tlb_mmu_finish() can mistakenly set fullmm incorrectly (if
mm_tlb_flush_nested() is true), which might skip the TLB flush.

Lucky for us, arm64 flushes each VMA separately (which as we discussed
separately may not be necessary), so the only PTEs that might not be flushed
are PTEs that are updated concurrently by another thread that also defer
their flushes. It therefore seems that the implications are more on the
correctness of certain syscalls (e.g., madvise(DONT_NEED)) without
implications on security or memory corruptions.

Let me know if you want me to send this patch separately with an updated
commit log for faster inclusion.

  reply	other threads:[~2021-02-02 21:36 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-31  0:11 [RFC 00/20] TLB batching consolidation and enhancements Nadav Amit
2021-01-31  0:11 ` [RFC 01/20] mm/tlb: fix fullmm semantics Nadav Amit
2021-01-31  1:02   ` Andy Lutomirski
2021-01-31  1:19     ` Nadav Amit
2021-01-31  2:57       ` Andy Lutomirski
2021-02-01  7:30         ` Nadav Amit
2021-02-01 11:36   ` Peter Zijlstra
2021-02-02  9:32     ` Nadav Amit
2021-02-02 11:00       ` Peter Zijlstra
2021-02-02 21:35         ` Nadav Amit [this message]
2021-02-03  9:44           ` Will Deacon
2021-02-04  3:20             ` Nadav Amit
2021-01-31  0:11 ` [RFC 02/20] mm/mprotect: use mmu_gather Nadav Amit
2021-01-31  0:11 ` [RFC 03/20] mm/mprotect: do not flush on permission promotion Nadav Amit
2021-01-31  1:07   ` Andy Lutomirski
2021-01-31  1:17     ` Nadav Amit
2021-01-31  2:59       ` Andy Lutomirski
     [not found]     ` <7a6de15a-a570-31f2-14d6-a8010296e694@citrix.com>
2021-02-01  5:58       ` Nadav Amit
2021-02-01 15:38         ` Andrew Cooper
2021-01-31  0:11 ` [RFC 04/20] mm/mapping_dirty_helpers: use mmu_gather Nadav Amit
2021-01-31  0:11 ` [RFC 05/20] mm/tlb: move BATCHED_UNMAP_TLB_FLUSH to tlb.h Nadav Amit
2021-01-31  0:11 ` [RFC 06/20] fs/task_mmu: use mmu_gather interface of clear-soft-dirty Nadav Amit
2021-01-31  0:11 ` [RFC 07/20] mm: move x86 tlb_gen to generic code Nadav Amit
2021-01-31 18:26   ` Andy Lutomirski
2021-01-31  0:11 ` [RFC 08/20] mm: store completed TLB generation Nadav Amit
2021-01-31 20:32   ` Andy Lutomirski
2021-02-01  7:28     ` Nadav Amit
2021-02-01 16:53       ` Andy Lutomirski
2021-02-01 11:52   ` Peter Zijlstra
2021-01-31  0:11 ` [RFC 09/20] mm: create pte/pmd_tlb_flush_pending() Nadav Amit
2021-01-31  0:11 ` [RFC 10/20] mm: add pte_to_page() Nadav Amit
2021-01-31  0:11 ` [RFC 11/20] mm/tlb: remove arch-specific tlb_start/end_vma() Nadav Amit
2021-02-01 12:09   ` Peter Zijlstra
2021-02-02  6:41     ` Nicholas Piggin
2021-02-02  7:20       ` Nadav Amit
2021-02-02  9:31         ` Peter Zijlstra
2021-02-02  9:54           ` Nadav Amit
2021-02-02 11:04             ` Peter Zijlstra
2021-01-31  0:11 ` [RFC 12/20] mm/tlb: save the VMA that is flushed during tlb_start_vma() Nadav Amit
2021-02-01 12:28   ` Peter Zijlstra
2021-01-31  0:11 ` [RFC 13/20] mm/tlb: introduce tlb_start_ptes() and tlb_end_ptes() Nadav Amit
2021-01-31  9:57   ` Damian Tometzki
2021-01-31 10:07   ` Damian Tometzki
2021-02-01  7:29     ` Nadav Amit
2021-02-01 13:19   ` Peter Zijlstra
2021-02-01 23:00     ` Nadav Amit
2021-01-31  0:11 ` [RFC 14/20] mm: move inc/dec_tlb_flush_pending() to mmu_gather.c Nadav Amit
2021-01-31  0:11 ` [RFC 15/20] mm: detect deferred TLB flushes in vma granularity Nadav Amit
2021-02-01 22:04   ` Nadav Amit
2021-02-02  0:14     ` Andy Lutomirski
2021-02-02 20:51       ` Nadav Amit
2021-02-04  4:35         ` Andy Lutomirski
2021-01-31  0:11 ` [RFC 16/20] mm/tlb: per-page table generation tracking Nadav Amit
2021-01-31  0:11 ` [RFC 17/20] mm/tlb: updated completed deferred TLB flush conditionally Nadav Amit
2021-01-31  0:11 ` [RFC 18/20] mm: make mm_cpumask() volatile Nadav Amit
2021-01-31  0:11 ` [RFC 19/20] lib/cpumask: introduce cpumask_atomic_or() Nadav Amit
2021-01-31  0:11 ` [RFC 20/20] mm/rmap: avoid potential races Nadav Amit
2021-08-23  8:05   ` Huang, Ying
2021-08-23 15:50     ` Nadav Amit
2021-08-24  0:36       ` Huang, Ying
2021-01-31  0:39 ` [RFC 00/20] TLB batching consolidation and enhancements Andy Lutomirski
2021-01-31  1:08   ` Nadav Amit
2021-01-31  3:30 ` Nicholas Piggin
2021-01-31  7:57   ` Nadav Amit
2021-01-31  8:14     ` Nadav Amit
2021-02-01 12:44     ` Peter Zijlstra
2021-02-02  7:14       ` Nicholas Piggin

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