From: Dmitry Safonov <dima@arista.com>
To: Brian Geffon <bgeffon@google.com>, Hugh Dickins <hughd@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Axel Rasmussen <axelrasmussen@google.com>,
Lokesh Gidra <lokeshgidra@google.com>,
Mike Rapoport <rppt@linux.vnet.ibm.com>,
Peter Xu <peterx@redhat.com>,
"Michael S . Tsirkin" <mst@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Andy Lutomirski <luto@amacapital.net>,
Vlastimil Babka <vbabka@suse.cz>,
Andrea Arcangeli <aarcange@redhat.com>,
Sonny Rao <sonnyrao@google.com>, Minchan Kim <minchan@kernel.org>,
"Kirill A . Shutemov" <kirill@shutemov.name>,
Michael Kerrisk <mtk.manpages@gmail.com>,
Alejandro Colomar <alx.manpages@gmail.com>
Subject: Re: [PATCH] mm: Allow shmem mappings with MREMAP_DONTUNMAP
Date: Tue, 16 Mar 2021 19:31:05 +0000 [thread overview]
Message-ID: <98716204-0440-9550-e067-41a984a29512@arista.com> (raw)
In-Reply-To: <CADyq12z+o0Rtziprkfs=PX2MPRPZyWBSgONYrRggZ8TEifq2sg@mail.gmail.com>
Hi Brian, Hugh,
On 3/16/21 7:18 PM, Brian Geffon wrote:
> Hi Hugh,
> Thanks for this suggestion, responses in line.
>
>> A better patch would say:
>>
>> - if (flags & MREMAP_DONTUNMAP && (!vma_is_anonymous(vma) ||
>> - vma->vm_flags & VM_SHARED))
>> + if ((flags & MREMAP_DONTUNMAP) &&
>> + (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP)))
>> return ERR_PTR(-EINVAL);
>>
>> VM_DONTEXPAND is what has long been used on special mappings, to prevent
>> surprises from mremap changing the size of the mapping: MREMAP_DONTUNMAP
>> introduced a different way of expanding the mapping, so VM_DONTEXPAND
>> still seems a reasonable name (I've thrown in VM_PFNMAP there because
>> it's in the VM_DONTEXPAND test lower down: for safety I guess, and best
>> if both behave the same - though one says -EINVAL and the other -EFAULT).
>
> I like this idea and am happy to mail a new patch. I think it may make
> sense to bring the lower block up here so that it becomes more clear
> that it's not duplicate code and that the MREMAP_DONTUNMAP case
> returns -EINVAL and other cases return -EFAULT. I wonder if the
> -EFAULT error code would have made more sense from the start for both
> cases, do you have any thoughts on changing the error code at this
> point?
>
>> With that VM_DONTEXPAND check in, Dmitry's commit cd544fd1dc92
>> ("mremap: don't allow MREMAP_DONTUNMAP on special_mappings and aio")
>> can still be reverted (as you agreed on 28th December), even though
>> vma_is_anonymous() will no longer protect it.
>
> I agree and if Dmitry does not have time I would be happy to mail a
> revert to cd544fd1dc92 as we discussed in [1]. Dmitry, would you like
> me to do that?
Ack. I was planning to send a patches set that includes the revert, but
that's stalled a bit. As the patch just adds excessive checks, but
doesn't introduce an issue, I haven't sent it separately.
Feel free to revert it :-)
Thanks,
Dmitry
next prev parent reply other threads:[~2021-03-16 19:31 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-03 17:52 [PATCH] mm: Allow shmem mappings with MREMAP_DONTUNMAP Brian Geffon
2021-03-03 18:13 ` Brian Geffon
2021-03-03 19:04 ` Lokesh Gidra
2021-03-14 4:19 ` Hugh Dickins
2021-03-16 19:18 ` Brian Geffon
2021-03-16 19:31 ` Dmitry Safonov [this message]
2021-03-16 20:17 ` Peter Xu
2021-03-19 1:58 ` Hugh Dickins
2021-03-17 19:13 ` [PATCH v2 1/2] mm: Allow non-VM_DONTEXPAND and VM_PFNMAP " Brian Geffon
2021-03-17 19:13 ` [PATCH v2 2/2] Revert "mremap: don't allow MREMAP_DONTUNMAP on special_mappings and aio" Brian Geffon
2021-03-17 20:40 ` [PATCH v2 1/2] mm: Allow non-VM_DONTEXPAND and VM_PFNMAP mappings with MREMAP_DONTUNMAP Peter Xu
2021-03-17 20:44 ` Brian Geffon
2021-03-17 21:18 ` Peter Xu
2021-03-17 21:25 ` Brian Geffon
2021-03-17 21:41 ` [PATCH v3 " Brian Geffon
2021-03-17 21:41 ` [PATCH v3 2/2] Revert "mremap: don't allow MREMAP_DONTUNMAP on special_mappings and aio" Brian Geffon
2021-03-19 1:28 ` Hugh Dickins
2021-03-17 22:03 ` [PATCH v3 1/2] mm: Allow non-VM_DONTEXPAND and VM_PFNMAP mappings with MREMAP_DONTUNMAP Andrew Morton
2021-03-19 1:20 ` Hugh Dickins
2021-03-23 16:26 ` [PATCH v4 1/3] mm: Extend MREMAP_DONTUNMAP to non-anonymous mappings Brian Geffon
2021-03-23 16:26 ` [PATCH v4 2/3] Revert "mremap: don't allow MREMAP_DONTUNMAP on special_mappings and aio" Brian Geffon
2021-03-23 18:16 ` Hugh Dickins
2021-03-23 16:26 ` [PATCH v4 3/3] selftests: Add a MREMAP_DONTUNMAP selftest for shmem Brian Geffon
2021-03-23 16:26 ` [PATCH] mremap.2: MREMAP_DONTUNMAP to reflect to supported mappings Brian Geffon
2021-03-23 18:25 ` [PATCH v5 1/3] mm: Extend MREMAP_DONTUNMAP to non-anonymous mappings Brian Geffon
2021-03-23 18:25 ` [PATCH v5 2/3] Revert "mremap: don't allow MREMAP_DONTUNMAP on special_mappings and aio" Brian Geffon
2021-03-23 19:05 ` Dmitry Safonov
2021-03-23 18:25 ` [PATCH v5 3/3] selftests: Add a MREMAP_DONTUNMAP selftest for shmem Brian Geffon
2021-03-23 18:25 ` [PATCH] mremap.2: MREMAP_DONTUNMAP to reflect to supported mappings Brian Geffon
2021-03-25 21:34 ` Alejandro Colomar (man-pages)
2021-03-26 18:08 ` Brian Geffon
2022-05-10 20:50 ` Brian Geffon
2021-03-23 19:04 ` [PATCH v5 1/3] mm: Extend MREMAP_DONTUNMAP to non-anonymous mappings Dmitry Safonov
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