Messages in this thread | | | Subject | Re: [PATCH] mm: migrate: add missing flush_dcache_page for non-mapped page migrate | From | Lars Persson <> | Date | Tue, 26 Feb 2019 09:40:30 +0100 |
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On 2/25/19 4:07 PM, Vlastimil Babka wrote: > On 2/19/19 1:32 PM, 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. >> >> Now recently we noticed that the /proc/sys/vm/compact_memory interface >> was quite efficient at provoking this class of userspace crashes. >> >> 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. >> >> 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. >> >> 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"). >> >> My proposed fix moves the D-cache maintenance inside move_to_new_page >> to make it common for both cases. >> >> Signed-off-by: Lars Persson <larper@axis.com> > > What about CC stable and a Fixes tag, would it be applicable here? >
Yes this is candidate for stable so let's add: Cc: <stable@vger.kernel.org>
I do not find a good candidate for a Fixes tag.
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