Messages in this thread | | | Date | Sat, 30 Dec 2006 22:46:04 +0000 | From | Russell King <> | Subject | Re: fuse, get_user_pages, flush_anon_page, aliasing caches and all that again |
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On Sat, Dec 30, 2006 at 10:26:20AM -0800, Linus Torvalds wrote: > > > On Sat, 30 Dec 2006, Russell King wrote: > > > > And here's the flush_anon_page() part. > > > > Add flush_anon_page() for ARM, to avoid data corruption issues when using > > fuse or other subsystems using get_user_pages(). > > Btw, since this doesn't actually change any code for anybody but ARM, just > adds a parameter that is obviously unused by everybody else, and if it > actually fixes a real bug for ARM, I'll obviously happily take it even > before 2.6.20. So go ahead put it in your ARM tree, and we'll get some > testing through that. And just ask me to pull at some point. > > I wonder why nobody else seems to have a "flush_anon_page()"? This would > seem to be a potential issue for architectures like sparc too.. Although > maybe sparc can do a flush by physical index with "flush_dcache_page()".
Well...
iirc, flush_anon_page() was introduced to fix non-working fuse on parisc, which occurs because fuse wants to use get_user_pages() to read data from the current processes memory space.
get_user_pages() contains a call to flush_dcache_page(), whose behaviour is defined for shared mappings. Anonymous pages are unspecified. It appears that flush_anon_page() was introduced to correct this oversight.
Looking at some of the other users of get_user_pages() which want to access the current processes memory space, one finds the following:
some use flush_cache_page(): - binfmt_elf coredump - ptrace (in arch code)
others don't: - aio - bio - block (block_dev::blk_get_page seems to be for direct-io, there's problems reported with this on ARM) - direct-io - fuse - vmsplice
So, anything except coredumps and ptrace are currently unsafe on ARM without something being added to get_user_pages() to ensure coherency of anonymous pages.
Given that we have reported corruption with direct-io, and debian bug #402876 for nonworking fuse, it seems the correct thing to do is to implement this function.
-- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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