Izik Eidus wrote: >> >> That's not quite what I was wondering. >> >> When you do an madvise() in userspace, the result is that when that >> memory is accessed again, linux will demand-fault in a zero page and >> COW it appropriately. If we do madvise() on the VA representing >> guest physical memory, what I'm curious about is whether the guest >> will actually see this change. If the guest happens to have the page >> mapped before we do the madvise(), what triggers KVM to kick any >> shadow page table entries out of it's cache? >> >> IIUC, today, after the madvise, the guest will have access to the old >> page until that entry gets evicted and reloaded from the shadow page >> table cache. > ok i am no familier with madvise() so i might talk nonsense but, > if the guest have the page mapped before the madvise(), this mean we > have high refernce to it, this is our only protection and as far as i > understand this should be enough
Right, we will have a reference to the page. But we want to propagate this change to the guest. So madvise() may be a bad example. What if you wanted to do shared memory for multiple guests. You start out with an anonymous mmap(), and you now what to mmap() a file in /dev/shm to be shared among multiple guests so you mmap(MAP_FIXED) to phys_ram_base + guest_pa in each guest. So what if guest_pa was in the guest's shadow page cache? In order for the guest to see the right hpa (the new shared memory), we have to be able to evict guest_pa. We could do this with something like mmu_unshadow(). What I don't understand, is how we can have something like mmu_unshadow() called automatically when an mmap() is initiated from userspace. We could just add an ioctl() to do it from userspace but I think it would be nicer if it Just Worked. Regards, Anthony Liguori > > > > ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
