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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
