Messages in this thread | | | From | Ingo Oeser <> | Subject | Re: mlockall and mmap of IO devices don't mix | Date | Sat, 4 Oct 2003 16:19:49 +0200 |
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Hi there,
CC'ed linux-mm and Andrew Morton for expertise.
On Saturday 04 October 2003 12:13, Russell King wrote: > It has to be correct. We do the following in a hell of a lot of places: > > pfn = pte_pfn(pte); > if (pfn_valid(pfn)) { > struct page *page = pfn_to_page(pfn); > /* do something with page */ > } > > basically this type of thing happens in any of the PTE manipulation > functions (eg, copy_page_range, zap_pte_range, etc.)
These functions are called always with pages, where we know, that this is RAM, AFICS. Since sometimes other things are encoded in the PTE, whe check this via pfn_valid().
If I'm wrong about this the gurus from LINUX-MM should complain loudly.
> If pfn_valid is returning false positives, and you happen to mmap() an > area which gives false positives from a user space application, your > kernel will either oops or will corrupt RAM when that application exits. > > I believe the comment in mmzone.h therefore is an opinion, and indicates > a concern for performance rather than correctness and stability.
I hope you are wrong about this, but I'm not totally sure. So I included the linux-mm mailing list and Andrew Morton for expert advice.
Regards
Ingo Oeser
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