From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sat, 16 Feb 2008 05:51:38 -0600 From: Robin Holt Subject: Re: [PATCH] KVM swapping with MMU Notifiers V7 Message-ID: <20080216115138.GA11391@sgi.com> References: <20080215064859.384203497@sgi.com> <20080216104827.GI11732@v2.random> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080216104827.GI11732@v2.random> Sender: owner-linux-mm@kvack.org Return-Path: To: Andrea Arcangeli Cc: Christoph Lameter , akpm@linux-foundation.org, Robin Holt , Avi Kivity , Izik Eidus , kvm-devel@lists.sourceforge.net, Peter Zijlstra , general@lists.openfabrics.org, Steve Wise , Roland Dreier , Kanoj Sarcar , steiner@sgi.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, daniel.blueman@quadrics.com List-ID: On Sat, Feb 16, 2008 at 11:48:27AM +0100, Andrea Arcangeli wrote: > Those below two patches enable KVM to swap the guest physical memory > through Christoph's V7. > > There's one last _purely_theoretical_ race condition I figured out and > that I'm wondering how to best fix. The race condition worst case is > that a few guest physical pages could remain pinned by sptes. The race > can materialize if the linux pte is zapped after get_user_pages > returns but before the page is mapped by the spte and tracked by > rmap. The invalidate_ calls can also likely be optimized further but > it's not a fast path so it's not urgent. I am doing this in xpmem with a stack-based structure in the function calling get_user_pages. That structure describes the start and end address of the range we are doing the get_user_pages on. If an invalidate_range_begin comes in while we are off to the kernel doing the get_user_pages, the invalidate_range_begin marks that structure indicating an invalidate came in. When the get_user_pages gets the structures relocked, it checks that flag (really a generation counter) and if it is set, retries the get_user_pages. After 3 retries, it returns -EAGAIN and the fault is started over from the remote side. Thanks, Robin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org