* Roman Kagan (rka...@virtuozzo.com) wrote: > On Tue, Feb 13, 2018 at 03:05:03PM +0000, Dr. David Alan Gilbert wrote: > > * Denis V. Lunev (d...@virtuozzo.com) wrote: > > > On 02/13/2018 05:59 PM, Dr. David Alan Gilbert wrote: > > > > * Daniel P. Berrangé (berra...@redhat.com) wrote: > > > >> That doesn't seem practical unless you can instantaneously write out > > > >> the entire guest RAM to disk without blocking, or can somehow snapshot > > > >> the RAM so you can write out a consistent view of the original RAM, > > > >> while the guest continues to dirty RAM pages. > > > > People have suggested doing something like that with userfault write > > > > mode; but the same would also be doable just by write protecting the > > > > whole of RAM and then following the faults. > > > > > > nope, userfault fd does not help :( We have tried, the functionality is > > > not > > > enough. Better to have small extension to KVM to protect all memory > > > and notify QEMU with accessed address. > > > > Can you explain why? I thought the write-protect mode of userfaultfd was > > supposed to be able to do that; cc'ing in Andrea > > IIRC it would if it worked; it just didn't when we tried.
Hmm that doesn't seem to be the ideal reason to create new KVM functionality, especially since there were a bunch of people wanting the userfaultfd-write mode for other uses. Dave > Roman. -- Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
