linux-kernel - Re: [PATCH v5 2/3] Revert "mremap: don't allow MREMAP_DONTUNMAP on special

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Date:   Tue, 23 Mar 2021 19:05:05 +0000
From:   Dmitry Safonov <0x7f454c46@...il.com>
To:     Brian Geffon <bgeffon@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Axel Rasmussen <axelrasmussen@...gle.com>,
        Lokesh Gidra <lokeshgidra@...gle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Peter Xu <peterx@...hat.com>, Hugh Dickins <hughd@...gle.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andy Lutomirski <luto@...capital.net>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Sonny Rao <sonnyrao@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Dmitry Safonov <dima@...sta.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Alejandro Colomar <alx.manpages@...il.com>
Subject: Re: [PATCH v5 2/3] Revert "mremap: don't allow MREMAP_DONTUNMAP on
 special_mappings and aio"

On 3/23/21 6:25 PM, Brian Geffon wrote:
> This reverts commit cd544fd1dc9293c6702fab6effa63dac1cc67e99.
> 
> As discussed in [1] this commit was a no-op because the mapping type was
> checked in vma_to_resize before move_vma is ever called. This meant that
> vm_ops->mremap() would never be called on such mappings. Furthermore,
> we've since expanded support of MREMAP_DONTUNMAP to non-anonymous
> mappings, and these special mappings are still protected by the existing
> check of !VM_DONTEXPAND and !VM_PFNMAP which will result in a -EINVAL.
> 
> 1. https://lkml.org/lkml/2020/12/28/2340
> 
> Signed-off-by: Brian Geffon <bgeffon@...gle.com>
> Acked-by: Hugh Dickins <hughd@...gle.com>

Reviewed-by: Dmitry Safonov <0x7f454c46@...il.com>

Thanks,
Dmitry