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Date: Thu, 4 Oct 2007 21:52:31 -0400 From: Rik van Riel <riel@...hat.com> To: Jeremy Fitzhardinge <jeremy@...p.org> Cc: Hugh Dickens <hugh@...itas.com>, David Rientjes <rientjes@...gle.com>, Zachary Amsden <zach@...are.com>, Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@...e.de>, Keir Fraser <keir@...source.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: race with page_referenced_one->ptep_test_and_clear_young and pagetable setup/pulldown On Thu, 04 Oct 2007 18:43:32 -0700 Jeremy Fitzhardinge <jeremy@...p.org> wrote: > It seems to me that there are a few ways to fix this: > > 1. Use asm-generic/pgtable.h when CONFIG_PARAVIRT is enabled. This > will clearly work, but is pretty blunt. > 2. Make test_and_clear_pte_flags a new paravirt-op, which can be > implemented in Xen as a hypercall, and as a raw > test_and_clear_bit for everyone else. The downside is adding yet > another pv-op. Either of these two would work. Another alternative could be to let test_and_clear_pte_flags have an exception table entry, where we jump right to the next instruction if the instruction clearing the flag fails. That is the essentially variant you need for Xen, except the fast path is still exactly the same it is as when running on native hardware. -- "Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." - Brian W. Kernighan - 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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