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received-spf: None (protection.outlook.com: wavecomp.com does not designate permitted sender hosts) authentication-results: spf=none (sender IP is ) smtp.mailfrom=pburton@wavecomp.com; x-ms-exchange-senderadcheck: 1 x-microsoft-antispam-message-info: JW9hGi75CRVl95jsZX74CeVCFw2/xM8XPjtAq424n7cW8CWfkmZ1kaoX6SmpKqfBfDxouyYd1Fw3ouvrDu0czh0C3JXABjn7W2bFRyWewWwwZE8nhpnPDDkqzN+H2TJAaVVK5d3HBaKC+dwKoBQ0iCELph0s/slTsfqV7/2JvlQShkuMlhGGSmfIeTut923cJkgZIt4HHIiR2txHsML51UvHbuB+JM89l5jr5SpO+SRMCrgPVbC9dtclFfQLe9TwD4n8jsfzFTEYuYeu/6P81LHppsja0CYr0OJBOXJbn7PvElI0FjoW11K+9eHF+u6ROCQOtWxdiVGWHtI//nzK9Ojt98DmegTut2h22ml1acg7O/yvxpg3kPuLni5rxS1qEQZsCdcDJ8WzKKnoZXlWS30gXV97zgHz1IVHfSmFy/Q= Content-Type: text/plain; charset="us-ascii" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: mips.com X-MS-Exchange-CrossTenant-Network-Message-Id: 00515087-bed6-4c29-5454-08d6983c34ec X-MS-Exchange-CrossTenant-originalarrivaltime: 21 Feb 2019 20:36:07.2306 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-id: 463607d3-1db3-40a0-8a29-970c56230104 X-MS-Exchange-Transport-CrossTenantHeadersStamped: MWHPR2201MB1021 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Hi Lars, On Tue, Feb 19, 2019 at 01:32:12PM +0100, Lars Persson wrote: > Our MIPS 1004Kc SoCs were seeing random userspace crashes with SIGILL > and SIGSEGV that could not be traced back to a userspace code > bug. They had all the magic signs of an I/D cache coherency issue. >=20 > Now recently we noticed that the /proc/sys/vm/compact_memory interface > was quite efficient at provoking this class of userspace crashes. >=20 > Studying the code in mm/migrate.c there is a distinction made between > migrating a page that is mapped at the instant of migration and one > that is not mapped. Our problem turned out to be the non-mapped pages. >=20 > For the non-mapped page the code performs a copy of the page content > and all relevant meta-data of the page without doing the required > D-cache maintenance. This leaves dirty data in the D-cache of the CPU > and on the 1004K cores this data is not visible to the I-cache. A > subsequent page-fault that triggers a mapping of the page will happily > serve the process with potentially stale code. >=20 > What about ARM then, this bug should have seen greater exposure? Well > ARM became immune to this flaw back in 2010, see commit c01778001a4f > ("ARM: 6379/1: Assume new page cache pages have dirty D-cache"). >=20 > My proposed fix moves the D-cache maintenance inside move_to_new_page > to make it common for both cases. >=20 > Signed-off-by: Lars Persson Reviewed-by: Paul Burton Thanks, Paul > --- > mm/migrate.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-)