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Date: Fri, 25 Jan 2008 09:18:04 +0000 From: "Jan Beulich" <jbeulich@...ell.com> To: "Nick Piggin" <nickpiggin@...oo.com.au> Cc: "Keir Fraser" <Keir.Fraser@...cam.ac.uk>, "Ingo Molnar" <mingo@...e.hu>, "Harvey Harrison" <harvey.harrison@...il.com>, "Jeremy Fitzhardinge" <jeremy@...p.org>, "Matt Mackall" <mpm@...enic.com>, "Andi Kleen" <ak@...e.de>, "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH UPDATE] x86: ignore spurious faults >>> Nick Piggin <nickpiggin@...oo.com.au> 25.01.08 09:38 >>> >On Friday 25 January 2008 19:15, Jan Beulich wrote: >> Actually, another thought: permitting (and handling) spurious faults for >> kernel mappings conflicts with NMI handling, i.e. great care would be >> needed to ensure the NMI path cannot touch any such mapping. So >> even the present Xen/Linux Dom0 implementation may have some >> (perhaps unlikely) problems here, and it would get worse if we added >> e.g. a virtual watchdog NMI (something I am considering, which would >> then extend the problem to DomU-s). > >Can you explain how they conflict? In the same way as vmalloc faults do (which is why vmalloc_sync_all() got introduced): a page fault nested inside an NMI will, by virtue of executing IRET, prematurely tell the processor that NMI handling is done (and specifically unmask further NMIs). Jan -- 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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