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Date: Tue, 29 Jul 2008 02:53:58 +0200 From: Johannes Weiner <hannes@...urebad.de> To: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Alexey Dobriyan <adobriyan@...il.com>, akpm@...uxfoundation.org, torvalds@...uxfoundation.org, npiggin@...e.de, linux-kernel@...r.kernel.org Subject: Re: [PATCH] x86: do not overrun page table ranges in gup Hi, Linus Torvalds <torvalds@...ux-foundation.org> writes: > On Tue, 29 Jul 2008, Johannes Weiner wrote: >> >> Actually, I think the prettier fix would be to just establish that >> garuantee: >> >> --- a/arch/x86/mm/gup.c >> +++ b/arch/x86/mm/gup.c >> @@ -223,7 +223,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write, >> struct page **pages) >> { >> struct mm_struct *mm = current->mm; >> - unsigned long end = start + (nr_pages << PAGE_SHIFT); >> + unsigned long end = PAGE_ALIGN(start + (nr_pages << PAGE_SHIFT)); > > Umm. 'end' is guaranteed to be page-aligned if 'start' is. > > So if this makes a difference, that implies that _start_ isn't > page-aligned, and then you when you add PAGE_SIZE to 'addr', you are going > to miss 'end' again. > > So no, the right fix would be to align 'start' first, which means that > everything else (including 'end') will be page-aligned. Aligning just one > or the other is very very wrong. Blah, I just should call it a day. Thanks for the explanation, you are right. Hannes -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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