From: Yang Shi <yang.shi@linux.alibaba.com>
To: Hugh Dickins <hughd@google.com>
Cc: aarcange@redhat.com, kirill.shutemov@linux.intel.com,
gavin.dg@linux.alibaba.com, akpm@linux-foundation.org,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [v2 PATCH] mm: thp: handle page cache THP correctly in PageTransCompoundMap
Date: Wed, 23 Oct 2019 13:50:14 -0700 [thread overview]
Message-ID: <d500d98e-3577-ced1-9614-7aa5e09e6dbe@linux.alibaba.com> (raw)
In-Reply-To: <alpine.LSU.2.11.1910231250260.1794@eggly.anvils>
On 10/23/19 1:00 PM, Hugh Dickins wrote:
> On Wed, 23 Oct 2019, Yang Shi wrote:
>> On 10/23/19 12:28 PM, Hugh Dickins wrote:
>>>> + return map_count >= 0 &&
>>> You have added a map_count >= 0 test there. Okay, not wrong, but not
>>> necessary, and not consistent with what's returned in the PageAnon
>>> case (if this were called for an unmapped page).
>> I was thinking about this too. I'm wondering there might be a case that the
>> PMD is split and it was the last PMD map, in this case subpage's _mapcount is
>> also equal to compound_mapcount (both is -1). So, it would return true, then
>> KVM may setup PMD map in EPT, but it might be PTE mapped later on the host.
>> But, I'm not quite sure if this is really possible or if this is really a
>> integrity problem. So, I thought it might be safer to add this check.
> The mmu_notifier_invalidate_range_start.._end() in __split_huge_pmd(),
> with KVM's locking and sequence counting, is required to protect
> against such races.
OK, it sounds safe. Thanks for confirming. Will post v4 soon.
>
> Hugh
prev parent reply other threads:[~2019-10-23 20:50 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-23 17:05 [v2 PATCH] mm: thp: handle page cache THP correctly in PageTransCompoundMap Yang Shi
2019-10-23 17:24 ` Matthew Wilcox
2019-10-23 17:57 ` Yang Shi
2019-10-23 18:57 ` Hugh Dickins
2019-10-23 19:28 ` Hugh Dickins
2019-10-23 19:37 ` Yang Shi
2019-10-23 20:00 ` Hugh Dickins
2019-10-23 20:50 ` Yang Shi [this message]
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=d500d98e-3577-ced1-9614-7aa5e09e6dbe@linux.alibaba.com \
--to=yang.shi@linux.alibaba.com \
--cc=aarcange@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=gavin.dg@linux.alibaba.com \
--cc=hughd@google.com \
--cc=kirill.shutemov@linux.intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=stable@vger.kernel.org \
/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).