From: Catalin Marinas <catalin.marinas@arm.com>
To: Jianyong Wu <Jianyong.Wu@arm.com>
Cc: Anshuman Khandual <Anshuman.Khandual@arm.com>,
"will@kernel.org" <will@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
"maz@kernel.org" <maz@kernel.org>,
"ardb@kernel.org" <ardb@kernel.org>,
"david@redhat.com" <david@redhat.com>,
"gshan@redhat.com" <gshan@redhat.com>,
Justin He <Justin.He@arm.com>, nd <nd@arm.com>
Subject: Re: [PATCH v1] arm64/mm: avoid race condition of update page table when kernel init
Date: Fri, 3 Dec 2021 17:44:11 +0000 [thread overview]
Message-ID: <YapXa8JWPNhkePwO@arm.com> (raw)
In-Reply-To: <AM9PR08MB72767A6DFA5A7ED8117E7C44F4869@AM9PR08MB7276.eurprd08.prod.outlook.com>
On Thu, Oct 28, 2021 at 08:36:07AM +0100, Jianyong Wu wrote:
> From Anshuman Khandual <anshuman.khandual@arm.com>:
> > On 10/27/21 3:18 PM, Jianyong Wu wrote:
> > > Race condition of page table update can happen in kernel boot period
> > > as both of memory hotplug action when kernel init and the
> > > mark_rodata_ro can update page table. For virtio-mem, the function excute flow chart is:
> > >
> > > -------------------------
> > > kernel_init
> > > kernel_init_freeable
> > > ...
> > > do_initcall
> > > ...
> > > module_init [A]
> > >
> > > ...
> > > mark_readonly
> > > mark_rodata_ro [B]
> > > -------------------------
[...]
> > > We can see that the error derived from the l3 translation as the pte
> > > value is *0*. That is because the fixmap has been clear when access.
> > >
> > > Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
> > > ---
> > > arch/arm64/mm/mmu.c | 2 ++
> > > 1 file changed, 2 insertions(+)
> > >
> > > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index
> > > cfd9deb347c3..567dfba8f08a 100644
> > > --- a/arch/arm64/mm/mmu.c
> > > +++ b/arch/arm64/mm/mmu.c
> > > @@ -564,8 +564,10 @@ void mark_rodata_ro(void)
> > > * to cover NOTES and EXCEPTION_TABLE.
> > > */
> > > section_size = (unsigned long)__init_begin - (unsigned long)__start_rodata;
> > > + get_online_mems();
> > > update_mapping_prot(__pa_symbol(__start_rodata), (unsigned long)__start_rodata,
> > > section_size, PAGE_KERNEL_RO);
> > > + put_online_mems();
> > >
> > > debug_checkwx();
> > > }
> >
> > While this should solve the current problem i.e race between concurrent
> > memory hotplug operation and mark_rodata_ro(), but I am still wondering
> > whether this is the fix at the right place and granularity. Basically a hotplug
> > operation queued in an work queue at [A] can execute during [B] is the root
> > cause of this problem.
>
> Not exactly, this issue doesn't only happen at the the *pure* kernel
> boot. For example, hotplug memory through VM monitor when VM boot. We
> can't foresee when that happen. Thus, this issue can affect all kinds
> of memory hotplug mechanism, including ACPI based memory hotplug and
> virtio-mem. I'm not sure that fix it here is the best way. If the race
> only happens between kernel init and memory hotplug, I think it's fine
> to fix it here. IMO, this issue results from the race for "fixmap"
> resource. I wonder why this global resource is not protected by a
> lock. Maybe we can add one and fix it there.
IIUC the race is caused by multiple attempts to use the fixmap at the
same time. We can add a fixmap_lock and hold it during
__create_pgd_mapping().
--
Catalin
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-12-03 17:45 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-27 9:48 [PATCH v1] arm64/mm: avoid race condition of update page table when kernel init Jianyong Wu
2021-10-28 5:57 ` Anshuman Khandual
2021-10-28 7:04 ` David Hildenbrand
2021-10-28 7:36 ` Jianyong Wu
2021-11-15 2:07 ` Jianyong Wu
2021-12-03 17:44 ` Catalin Marinas [this message]
2021-12-03 18:13 ` David Hildenbrand
2021-12-06 15:14 ` Catalin Marinas
2021-12-06 2:11 ` Jianyong Wu
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=YapXa8JWPNhkePwO@arm.com \
--to=catalin.marinas@arm.com \
--cc=Anshuman.Khandual@arm.com \
--cc=Jianyong.Wu@arm.com \
--cc=Justin.He@arm.com \
--cc=ardb@kernel.org \
--cc=david@redhat.com \
--cc=gshan@redhat.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=maz@kernel.org \
--cc=nd@arm.com \
--cc=will@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).