On Tue, 15 Jan 2008, Avi Kivity wrote: > > But each guest has its own page structs. They cannot share page structs. > > Concurrent access of two independent kernel instances for synchronization > > and status maintenance to a single page struct? > > > > There's a host page struct (that the guest know nothing about and cannot > touch), and optionally a guest page struct for each guest (that the host and > the other guest know nothing about).
Ok so if two linux guests want to share memory three page structs are involved: 1. Host page struct 2. Guest #1 page struct 3. Guest #2 page struct I can understand that 1 and 2 point to the same physical page. Even all three could point to the same page if the page is readonly. However, lets say that Guest #1 allocates some anonymous memory and wants to share it with Guest #2. In that case something like PFNMAP is likely going to be used? Or are you remapping the physical page so that #1 and #2 share it? In that case two page struct describe state of the same physical page and we have no effective synchronization for writeback etc. > The host page struct may disappear if the host decides to swap the page into > its backing store and free the page. The guest page structs (if any) would > remain. Page structs never disappear. The pte's may disappear and the page may be unmapped from an address space of a process but the page struct stays. Page struct can only disappear if memory hotplug is activated and memory is taken out of the system. ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
