From: Andrew Morton <akpm@linux-foundation.org>
To: liusongtang <liusongtang@huawei.com>
Cc: <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
<nixiaoming@huawei.com>, <young.liuyang@huawei.com>,
<wangkefeng@huawei.com>
Subject: Re: [PATCH] mm/mprotect: reduce Committed_AS if memory protection is changed to PROT_NONE
Date: Tue, 26 Apr 2022 13:34:01 -0700 [thread overview]
Message-ID: <20220426133401.9404190c5a5c6ff58b694c59@linux-foundation.org> (raw)
In-Reply-To: <20220426112705.3323-1-liusongtang@huawei.com>
On Tue, 26 Apr 2022 19:27:05 +0800 liusongtang <liusongtang@huawei.com> wrote:
> If PROT_WRITE is set, the size of vm area will be added to Committed_AS.
> However, if memory protection is changed to PROT_NONE,
> the corresponding physical memory will not be used, but Committed_AS still
> count the size of the PROT_NONE memory.
>
> This patch reduce Committed_AS and free the corresponding memory if
> memory protection is changed to PROT_NONE.
>
> ...
>
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -497,6 +497,12 @@ mprotect_fixup(struct vm_area_struct *vma, struct vm_area_struct **pprev,
> }
>
> success:
> + if ((newflags & (VM_READ | VM_WRITE | VM_EXEC | VM_LOCKED | VM_ACCOUNT)) == VM_ACCOUNT) {
> + zap_page_range(vma, start, end - start);
> + newflags &= ~VM_ACCOUNT;
> + vm_unacct_memory((end - start) >> PAGE_SHIFT);
> + }
> +
> /*
> * vm_flags and vm_page_prot are protected by the mmap_lock
> * held in write mode.
Surprised. If userspace does mprotect(addr, len. PROT_NONE) then
mprotect(addr, len. PROT_READ), what is now at *addr? Zeroes?
next prev parent reply other threads:[~2022-04-26 20:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-26 11:27 [PATCH] mm/mprotect: reduce Committed_AS if memory protection is changed to PROT_NONE liusongtang
2022-04-26 20:34 ` Andrew Morton [this message]
2022-04-27 6:34 ` liusongtang
2022-05-03 18:35 ` David Hildenbrand
2022-04-30 15:41 ` [mm/mprotect] 5e1e18b334: kvm-unit-tests.eventinj.fail kernel test robot
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=20220426133401.9404190c5a5c6ff58b694c59@linux-foundation.org \
--to=akpm@linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=liusongtang@huawei.com \
--cc=nixiaoming@huawei.com \
--cc=wangkefeng@huawei.com \
--cc=young.liuyang@huawei.com \
/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).