From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f69.google.com (mail-oi0-f69.google.com [209.85.218.69]) by kanga.kvack.org (Postfix) with ESMTP id 008E46B0038 for ; Sun, 26 Feb 2017 23:27:15 -0500 (EST) Received: by mail-oi0-f69.google.com with SMTP id m124so26201389oig.3 for ; Sun, 26 Feb 2017 20:27:15 -0800 (PST) Received: from NAM02-BL2-obe.outbound.protection.outlook.com (mail-bl2nam02on0128.outbound.protection.outlook.com. [104.47.38.128]) by mx.google.com with ESMTPS id r18si1605099otc.62.2017.02.26.20.27.12 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Sun, 26 Feb 2017 20:27:12 -0800 (PST) From: Zi Yan Subject: Re: Is MADV_HWPOISON supposed to work only on faulted-in pages? Date: Sun, 26 Feb 2017 22:27:02 -0600 Message-ID: <22763879-C335-41E6-8102-2022EED75DAE@cs.rutgers.edu> In-Reply-To: <20170227012029.GA28934@hori1.linux.bs1.fc.nec.co.jp> References: <6a445beb-119c-9a9a-0277-07866afe4924@redhat.com> <20170220050016.GA15533@hori1.linux.bs1.fc.nec.co.jp> <20170223032342.GA18740@hori1.linux.bs1.fc.nec.co.jp> <1ba376aa-5e7c-915f-35d1-2d4eef0cad88@huawei.com> <20170227012029.GA28934@hori1.linux.bs1.fc.nec.co.jp> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=_MailMate_1523C952-EB8A-4F67-AF55-E5482DFF313B_="; micalg=pgp-sha512; protocol="application/pgp-signature" Sender: owner-linux-mm@kvack.org List-ID: To: Naoya Horiguchi Cc: Yisheng Xie , Jan Stancek , "linux-mm@kvack.org" , "ltp@lists.linux.it" --=_MailMate_1523C952-EB8A-4F67-AF55-E5482DFF313B_= Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 26 Feb 2017, at 19:20, Naoya Horiguchi wrote: > On Sat, Feb 25, 2017 at 10:28:15AM +0800, Yisheng Xie wrote: >> hi Naoya, >> >> On 2017/2/23 11:23, Naoya Horiguchi wrote: >>> On Mon, Feb 20, 2017 at 05:00:17AM +0000, Horiguchi Naoya(=E5=A0=80=E5= =8F=A3 =E7=9B=B4=E4=B9=9F) wrote: >>>> On Tue, Feb 14, 2017 at 04:41:29PM +0100, Jan Stancek wrote: >>>>> Hi, >>>>> >>>>> code below (and LTP madvise07 [1]) doesn't produce SIGBUS, >>>>> unless I touch/prefault page before call to madvise(). >>>>> >>>>> Is this expected behavior? >>>> >>>> Thank you for reporting. >>>> >>>> madvise(MADV_HWPOISON) triggers page fault when called on the addres= s >>>> over which no page is faulted-in, so I think that SIGBUS should be >>>> called in such case. >>>> >>>> But it seems that memory error handler considers such a page as "res= erved >>>> kernel page" and recovery action fails (see below.) >>>> >>>> [ 383.371372] Injecting memory failure for page 0x1f10 at 0x7efcd= c569000 >>>> [ 383.375678] Memory failure: 0x1f10: reserved kernel page still = referenced by 1 users >>>> [ 383.377570] Memory failure: 0x1f10: recovery action for reserve= d kernel page: Failed >>>> >>>> I'm not sure how/when this behavior was introduced, so I try to unde= rstand. >>> >>> I found that this is a zero page, which is not recoverable for memory= >>> error now. >>> >>>> IMO, the test code below looks valid to me, so no need to change. >>> >>> I think that what the testcase effectively does is to test whether me= mory >>> handling on zero pages works or not. >>> And the testcase's failure seems acceptable, because it's simply not-= implemented yet. >>> Maybe recovering from error on zero page is possible (because there's= no data >>> loss for memory error,) but I'm not sure that code might be simple en= ough and/or >>> it's worth doing ... >> I question about it, if a memory error happened on zero page, it will= >> cause all of data read from zero page is error, I mean no-zero, right?= > > Hi Yisheng, > > Yes, the impact is serious (could affect many processes,) but it's poss= ibility > is very low because there's only one page in a system that is used for = zero page. > There are many other pages which are not recoverable for memory error l= ike > slab pages, so I'm not sure how I prioritize it (maybe it's not a > top-priority thing, nor low-hanging fruit.) > >> And can we just use re-initial it with zero data maybe by memset ? > > Maybe it's not enoguh. Under a real hwpoison, we should isolate the err= or > page to prevent the access on the broken data. > But zero page is statically defined as an array of global variable, so > it's not trival to replace it with a new zero page at runtime. > > Anyway, it's in my todo list, so hopefully revisited in the future. > Hi Naoya, The test case tries to HWPOISON a range of virtual addresses that do not map to any physical pages. I expected either madvise should fail because HWPOISON does not work on non-existing physical pages or madvise_hwpoison() should populate some physical pages for that virtual address range and poison them. As I tested it on kernel v4.10, the test application exited at madvise, because madvise returns -1 and error message is "Device or resource busy". I think this is a proper behavior. There might be some confusion in madvise's man page on MADV_HWPOISON. If you add some text saying madvise fails if any page is not mapped in the given address range, that can eliminate the confusion. -- Best Regards Yan Zi --=_MailMate_1523C952-EB8A-4F67-AF55-E5482DFF313B_= Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQEcBAEBCgAGBQJYs6qXAAoJEEGLLxGcTqbMi+cH/2LydO8wB9pA2qI+hQha6zT7 inLGbVPinD8VxXr/pYCSNUq/D9tvRD2JPR4YLv4syaHYB6V3so31nyyG0oUlniEZ Rpw4wWwuBDa8T556XFKbgQgka7INSvPmepdqSeUjSSPvD0KoDMSOcuPLfZfrgZwT T+Y+FXkiwz7SpQDjb7puT4yJDc3mTeq0W73S4udqPq24CIVjIi2jxate3v9aqYsL v5WCUjOeU1AiYgAgkJ3Sb3xPyHdxJZ1+uD3W2YxW0AwQRryFAtGw/pQdNHOMx4BS uFYQNsD2569EoaPR+Z+KTY23TP6wRil59/QLGv1l9jF9La4MIMs7bCmGn5ueiAA= =QLzN -----END PGP SIGNATURE----- --=_MailMate_1523C952-EB8A-4F67-AF55-E5482DFF313B_=-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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