[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Shadow Page Tables in Xen
On Fri, Apr 24, 2009 at 6:33 AM, priya sehgal <priyagps@xxxxxxxxxxx> wrote: > >> Ok that seems, but please note that at the moment shadows >> always set the DIRTY bit (unless we're tracking a VRAM >> address), so you might have to set the dirty bit clean when >> propagating the shadow, which is a bit too intrusive >> perhaps. But yes, that would work. >> > > I see one problem, which we might introduce by making the SPTE entries of > all the pages in the group RW, but not marking their corresponding GPTE entry > as DIRTY -- if the Guest writes to a page (marked as RW in SPTE) and makes it > dirty, there is no way Hypervisor will know about it, and so it cannot mark > GPTE's entry as DIRTY. This might lead to inconsistency between the shadow > and guest page tables. Also, the OS running inside the guest will not see > correct picture about the dirty pages, thereby not flushing the dirty pages. Yes, that's a common problem when you "prefetch" write accesses in shadows. You can just set dirty (as in log_dirty) pages that have guest's ptes dirty. Of course you must be very careful in case you have an entry coming from a splintered L1 in shadow (that is the guest sets the PSE bit) because in that case you have to check at the guest L2 (guest PDE level) the dirty bit. Anyway, I think it's kind of clear that I was trying to convince you to the idea of getting rid of shadow_blow_tables at each log dirty cleanup, since this feature you have in mind is both intrusive and very specific, and perhaps not worth it. Of course, you might prove my non-proved assumption wrong. :) Thanks, Gianluca -- It was a type of people I did not know, I found them very strange and they did not inspire confidence at all. Later I learned that I had been introduced to electronic engineers. E. W. Dijkstra _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
|
Lists.xenproject.org is hosted with RackSpace, monitoring our |