linux-kernel - Re: [PATCH v6 0/7] fixes of TLB batching races

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Date:   Thu, 3 Aug 2017 08:26:24 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Nadav Amit <namit@...are.com>
Cc:     linux-mm@...ck.org, nadav.amit@...il.com,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH v6 0/7] fixes of TLB batching races

On Tue, Aug 01, 2017 at 05:08:11PM -0700, Nadav Amit wrote:
> It turns out that Linux TLB batching mechanism suffers from various races.
> Races that are caused due to batching during reclamation were recently
> handled by Mel and this patch-set deals with others. The more fundamental
> issue is that concurrent updates of the page-tables allow for TLB flushes
> to be batched on one core, while another core changes the page-tables.
> This other core may assume a PTE change does not require a flush based on
> the updated PTE value, while it is unaware that TLB flushes are still
> pending.
> 
> This behavior affects KSM (which may result in memory corruption) and
> MADV_FREE and MADV_DONTNEED (which may result in incorrect behavior). A
> proof-of-concept can easily produce the wrong behavior of MADV_DONTNEED.
> Memory corruption in KSM is harder to produce in practice, but was observed
> by hacking the kernel and adding a delay before flushing and replacing the
> KSM page.
> 
> Finally, there is also one memory barrier missing, which may affect
> architectures with weak memory model.
> 
> v5 -> v6:
> * Combining with Minchan Kim's patch set, adding ack's (Andrew)
> * Minor: missing header, typos (Nadav)
> * Renaming arch_generic_tlb_finish_mmu (Mel)

Thanks for intergrating/correction, Nadav.