From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>, Ajay Kaher <akaher@vmware.com>
Cc: gregkh@linuxfoundation.org, stable@vger.kernel.org,
torvalds@linux-foundation.org, punit.agrawal@arm.com,
akpm@linux-foundation.org, kirill.shutemov@linux.intel.com,
willy@infradead.org, will.deacon@arm.com, mszeredi@redhat.com,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
srivatsab@vmware.com, srivatsa@csail.mit.edu,
amakhalov@vmware.com, srinidhir@vmware.com, bvikas@vmware.com,
anishs@vmware.com, vsirnapalli@vmware.com, srostedt@vmware.com,
Vlastimil Babka <vbabka@suse.cz>,
Oscar Salvador <osalvador@suse.de>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Juergen Gross <jgross@suse.com>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH v3 8/8] x86, mm, gup: prevent get_page() race with munmap in paravirt guest
Date: Mon, 16 Dec 2019 14:30:44 +0100 [thread overview]
Message-ID: <87lfrc9z3v.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20191216130443.GN2844@hirez.programming.kicks-ass.net>
Peter Zijlstra <peterz@infradead.org> writes:
> On Tue, Dec 17, 2019 at 02:15:48AM +0530, Ajay Kaher wrote:
>> From: Vlastimil Babka <vbabka@suse.cz>
>>
>> The x86 version of get_user_pages_fast() relies on disabled interrupts to
>> synchronize gup_pte_range() between gup_get_pte(ptep); and get_page() against
>> a parallel munmap. The munmap side nulls the pte, then flushes TLBs, then
>> releases the page. As TLB flush is done synchronously via IPI disabling
>> interrupts blocks the page release, and get_page(), which assumes existing
>> reference on page, is thus safe.
>> However when TLB flush is done by a hypercall, e.g. in a Xen PV guest, there is
>> no blocking thanks to disabled interrupts, and get_page() can succeed on a page
>> that was already freed or even reused.
>>
>> We have recently seen this happen with our 4.4 and 4.12 based kernels, with
>> userspace (java) that exits a thread, where mm_release() performs a futex_wake()
>> on tsk->clear_child_tid, and another thread in parallel unmaps the page where
>> tsk->clear_child_tid points to. The spurious get_page() succeeds, but futex code
>> immediately releases the page again, while it's already on a freelist. Symptoms
>> include a bad page state warning, general protection faults acessing a poisoned
>> list prev/next pointer in the freelist, or free page pcplists of two cpus joined
>> together in a single list. Oscar has also reproduced this scenario, with a
>> patch inserting delays before the get_page() to make the race window larger.
>>
>> Fix this by removing the dependency on TLB flush interrupts the same way as the
>
> This is suppsed to be fixed by:
>
> arch/x86/Kconfig: select HAVE_RCU_TABLE_FREE if PARAVIRT
>
Yes,
but HAVE_RCU_TABLE_FREE was enabled on x86 only in 4.14:
commit 9e52fc2b50de3a1c08b44f94c610fbe998c0031a
Author: Vitaly Kuznetsov <vkuznets@redhat.com>
Date: Mon Aug 28 10:22:51 2017 +0200
x86/mm: Enable RCU based page table freeing (CONFIG_HAVE_RCU_TABLE_FREE=y)
and, if I understood correctly, Ajay is suggesting the patch for older
stable kernels (4.9 and 4.4 I would guess).
--
Vitaly
next prev parent reply other threads:[~2019-12-16 13:30 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-16 20:45 [PATCH v3 0/8] Backported fixes for 4.4 stable tree Ajay Kaher
2019-12-16 20:45 ` [PATCH v3 1/8] mm: make page ref count overflow check tighter and more explicit Ajay Kaher
2019-12-16 20:45 ` [PATCH v3 2/8] mm: add 'try_get_page()' helper function Ajay Kaher
2019-12-16 20:45 ` [PATCH v3 3/8] mm, gup: remove broken VM_BUG_ON_PAGE compound check for hugepages Ajay Kaher
2019-12-16 20:45 ` [PATCH v3 4/8] mm, gup: ensure real head page is ref-counted when using hugepages Ajay Kaher
2019-12-16 20:45 ` [PATCH v3 5/8] mm: prevent get_user_pages() from overflowing page refcount Ajay Kaher
2019-12-16 20:45 ` [PATCH v3 6/8] pipe: add pipe_buf_get() helper Ajay Kaher
2019-12-16 20:45 ` [PATCH v3 7/8] fs: prevent page refcount overflow in pipe_buf_get Ajay Kaher
2019-12-16 20:45 ` [PATCH v3 8/8] x86, mm, gup: prevent get_page() race with munmap in paravirt guest Ajay Kaher
2019-12-16 13:04 ` Peter Zijlstra
2019-12-16 13:30 ` Vitaly Kuznetsov [this message]
2019-12-16 13:47 ` Peter Zijlstra
2019-12-16 15:11 ` Vlastimil Babka
2019-12-16 16:08 ` Vitaly Kuznetsov
2019-12-17 4:13 ` Ajay Kaher
2020-01-31 12:51 ` Ajay Kaher
[not found] <1575999773-4628-1-git-send-email-akaher@vmware.com>
2019-12-10 17:42 ` Ajay Kaher
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=87lfrc9z3v.fsf@vitty.brq.redhat.com \
--to=vkuznets@redhat.com \
--cc=akaher@vmware.com \
--cc=akpm@linux-foundation.org \
--cc=amakhalov@vmware.com \
--cc=anishs@vmware.com \
--cc=bp@alien8.de \
--cc=bvikas@vmware.com \
--cc=dave.hansen@linux.intel.com \
--cc=gregkh@linuxfoundation.org \
--cc=jgross@suse.com \
--cc=kirill.shutemov@linux.intel.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=luto@kernel.org \
--cc=mingo@redhat.com \
--cc=mszeredi@redhat.com \
--cc=osalvador@suse.de \
--cc=peterz@infradead.org \
--cc=punit.agrawal@arm.com \
--cc=srinidhir@vmware.com \
--cc=srivatsa@csail.mit.edu \
--cc=srivatsab@vmware.com \
--cc=srostedt@vmware.com \
--cc=stable@vger.kernel.org \
--cc=tglx@linutronix.de \
--cc=torvalds@linux-foundation.org \
--cc=vbabka@suse.cz \
--cc=vsirnapalli@vmware.com \
--cc=will.deacon@arm.com \
--cc=willy@infradead.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).