From: Anshuman Khandual <khandual@linux.vnet.ibm.com>
To: Mike Kravetz <mike.kravetz@oracle.com>,
Vlastimil Babka <vbabka@suse.cz>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Michal Hocko <mhocko@suse.com>, Aaron Lu <aaron.lu@intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Anshuman Khandual <khandual@linux.vnet.ibm.com>,
Linux API <linux-api@vger.kernel.org>
Subject: Re: [PATCH] mm/mremap: Fail map duplication attempts for private mappings
Date: Fri, 14 Jul 2017 10:21:26 +0530 [thread overview]
Message-ID: <b4470a3e-ce80-e3d4-c5ea-6cb8b5ced8ad@linux.vnet.ibm.com> (raw)
In-Reply-To: <415625d2-1be9-71f0-ca11-a014cef98a3f@oracle.com>
On 07/14/2017 04:03 AM, Mike Kravetz wrote:
> On 07/13/2017 12:11 PM, Vlastimil Babka wrote:
>> [+CC linux-api]
>>
>> On 07/13/2017 05:58 PM, Mike Kravetz wrote:
>>> mremap will create a 'duplicate' mapping if old_size == 0 is
>>> specified. Such duplicate mappings make no sense for private
>>> mappings. If duplication is attempted for a private mapping,
>>> mremap creates a separate private mapping unrelated to the
>>> original mapping and makes no modifications to the original.
>>> This is contrary to the purpose of mremap which should return
>>> a mapping which is in some way related to the original.
>>>
>>> Therefore, return EINVAL in the case where if an attempt is
>>> made to duplicate a private mapping.
>>>
>>> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
>> Acked-by: Vlastimil Babka <vbabka@suse.cz>
>>
> In another e-mail thread, Andrea makes the case that mremap(old_size == 0)
> of private file backed mappings could possibly be used for something useful.
> For example to create a private COW mapping. Of course, a better way to do
> this would be simply using the fd to create a private mapping.
>
> If returning EINVAL for all private mappings is too general, the following
> patch adds a check to only return EINVAL for private anon mappings.
>
> mm/mremap: Fail map duplication attempts for private anon mappings
>
> mremap will create a 'duplicate' mapping if old_size == 0 is
> specified. Such duplicate mappings make no sense for private
> anonymous mappings. If duplication is attempted for a private
> anon mapping, mremap creates a separate private mapping unrelated
> to the original mapping and makes no modifications to the original.
> This is contrary to the purpose of mremap which should return a
> mapping which is in some way related to the original.
>
> Therefore, return EINVAL in the case where an attempt is made to
> duplicate a private anon mapping.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> ---
> mm/mremap.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/mm/mremap.c b/mm/mremap.c
> index cd8a1b1..586ea3d 100644
> --- a/mm/mremap.c
> +++ b/mm/mremap.c
> @@ -383,6 +383,14 @@ static struct vm_area_struct *vma_to_resize(unsigned long addr,
> if (!vma || vma->vm_start > addr)
> return ERR_PTR(-EFAULT);
>
> + /*
> + * !old_len is a special case where a mapping is 'duplicated'.
> + * Do not allow this for private anon mappings.
> + */
> + if (!old_len && vma_is_anonymous(vma) &&
> + !(vma->vm_flags & (VM_SHARED | VM_MAYSHARE)))
> + return ERR_PTR(-EINVAL);
Sounds better compared to rejecting everything private.
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2017-07-14 4:51 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1499961495-8063-1-git-send-email-mike.kravetz@oracle.com>
[not found] ` <1499961495-8063-1-git-send-email-mike.kravetz-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2017-07-13 19:11 ` [PATCH] mm/mremap: Fail map duplication attempts for private mappings Vlastimil Babka
2017-07-13 22:33 ` Mike Kravetz
2017-07-14 4:51 ` Anshuman Khandual [this message]
[not found] ` <415625d2-1be9-71f0-ca11-a014cef98a3f-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2017-07-14 8:26 ` Michal Hocko
2017-07-14 17:29 ` Mike Kravetz
2017-07-17 6:44 ` Michal Hocko
2017-07-19 16:39 ` Mike Kravetz
2017-07-20 8:20 ` Michal Hocko
2017-07-20 20:37 ` [PATCH v2] " Mike Kravetz
2017-07-21 14:36 ` Michal Hocko
2017-07-21 21:18 ` Mike Kravetz
[not found] ` <cb9d9f6a-7095-582f-15a5-62643d65c736-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
2017-07-24 8:50 ` Michal Hocko
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=b4470a3e-ce80-e3d4-c5ea-6cb8b5ced8ad@linux.vnet.ibm.com \
--to=khandual@linux.vnet.ibm.com \
--cc=aarcange@redhat.com \
--cc=aaron.lu@intel.com \
--cc=akpm@linux-foundation.org \
--cc=kirill.shutemov@linux.intel.com \
--cc=linux-api@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@suse.com \
--cc=mike.kravetz@oracle.com \
--cc=vbabka@suse.cz \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).