On Fri 23-09-16 20:29:20, zijun_hu wrote: > On 2016/9/23 16:45, Michal Hocko wrote: > > On Thu 22-09-16 23:13:17, zijun_hu wrote: > >> On 2016/9/22 20:47, Michal Hocko wrote: > >>> On Wed 21-09-16 12:19:53, zijun_hu wrote: > >>>> From: zijun_hu <zijun_hu@xxxxxxx> > >>>> > >>>> endless loop maybe happen if either of parameter addr and end is not > >>>> page aligned for kernel API function ioremap_page_range() > >>> > >>> Does this happen in practise or this you found it by reading the code? > >>> > >> i found it by reading the code, this is a kernel API function and there > >> are no enough hint for parameter requirements, so any parameters > >> combination maybe be used by user, moreover, it seems appropriate for > >> many bad parameter combination, for example, provided PMD_SIZE=2M and > >> PAGE_SIZE=4K, 0x00 is used for aligned very well address > >> a user maybe want to map virtual range[0x1ff800, 0x200800) to physical address > >> 0x300800, it will cause endless loop > > > > Well, we are relying on the kernel to do the sane thing otherwise we > > would be screwed anyway. If this can be triggered by a userspace then it > > would be a different story. Just look at how we are doing mmap, we > > sanitize the page alignment at the high level and the lower level > > functions just assume sane values. > > > ioremap_page_range() is exported by EXPORT_SYMBOL_GPL() as a kernel interface > so perhaps it is called by not only any kernel module authors but also other > kernel parts > > if the bad range is used by a careless kernel user really, it seems a better > choice to alert the warning message or panic the kernel than hanging the system > due to endless loop, it can help them locate problem usefully I absolutely do not want to panic my system just because a crapy module or whatnot doesn't provide an aligned address. Warning and a fixup sounds much more sane to me. [...] > >> no, it don't work for many special case > >> for example, provided PMD_SIZE=2M > >> mapping [0x1f8800, 0x208800) virtual range will be split to two ranges > >> [0x1f8800, 0x200000) and [0x200000,0x208800) and map them separately > >> the first range will cause dead loop > > > > I am not sure I see your point. How can we deadlock if _both_ addresses > > get aligned to the page boundary and how does PMD_SIZE make any > > difference. > > > i will take a example to illustrate my considerations > provided PUD_SIZE == 1G, PMD_SIZE == 2M, PAGE_SIZE == 4K > it is used by arm64 normally > > we want to map virtual range [0xffffffff_ffc08800, 0xffffffff_fffff800) by > ioremap_page_range(),ioremap_pmd_range() is called to map the range > finally, ioremap_pmd_range() will call > ioremap_pte_range(pmd, 0xffffffff_ffc08800, 0xffffffff_fffe0000) and > ioremap_pte_range(pmd, 0xffffffff_fffe0000, 0xffffffff fffff800) separately but those ranges are not aligned and it ioremap_page_range fix them up to _be_ aligned then there is no problem, right? So either I am missing something or we are talking past each other. -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>