On Tue, Feb 19, 2008 at 05:40:50PM -0600, Jack Steiner wrote: > On Wed, Feb 20, 2008 at 12:11:57AM +0100, Nick Piggin wrote: > > On Tue, Feb 19, 2008 at 02:58:51PM +0100, Andrea Arcangeli wrote: > > > On Tue, Feb 19, 2008 at 09:43:57AM +0100, Nick Piggin wrote: > > > > anything when changing the pte to be _more_ permissive, and I don't > > > > > > Note that in my patch the invalidate_pages in mprotect can be > > > trivially switched to a mprotect_pages with proper params. This will > > > prevent page faults completely in the secondary MMU (there will only > > > be tlb misses after the tlb flush just like for the core linux pte), > > > and it'll allow all the secondary MMU pte blocks (512/1024 at time > > > with my PT lock design) to be updated to have proper permissions > > > matching the core linux pte. > > > > Sorry, I realise I still didn't get this through my head yet (and also > > have not seen your patch recently). So I don't know exactly what you > > are doing... > > > > But why does _anybody_ (why does Christoph's patches) need to invalidate > > when they are going to be more permissive? This should be done lazily by > > the driver, I would have thought. > > > Agree. Although for most real applications, the performance difference > is probably negligible.
But importantly, doing it that way means you share test coverage with the CPU TLB flushing code, and you don't introduce a new concept to the VM. So, it _has_ to be lazy flushing, IMO (as there doesn't seem to be a good reason otherwise). mprotect shouldn't really be a special case, because it still has to flush the CPU tlbs as well when restricting access. ------------------------------------------------------------------------- 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