On Thu, Sep 10, 2020 at 02:27:48PM +0100, Dr. David Alan Gilbert wrote: > * Andrew Jones (drjones@xxxxxxxxxx) wrote: > > On Wed, Sep 09, 2020 at 06:45:33PM -0700, Richard Henderson wrote: > > > On 9/9/20 8:25 AM, Andrew Jones wrote: > > > >> * Provide a KVM-specific method to extract the tags from guest memory. > > > >> This might also have benefits in terms of providing an easy way to > > > >> read bulk tag data from guest memory (since the LDGM instruction > > > >> isn't available at EL0). > > > > > > > > Maybe we need a new version of KVM_GET_DIRTY_LOG that also provides > > > > the tags for all addresses of each dirty page. > > > > > > KVM_GET_DIRTY_LOG just provides one bit per dirty page, no? Then VMM copies > > > the data out from its local address to guest memory. > > > > > > There'd be no difference with or without tags, afaik. It's just about how VMM > > > copies the data, with or without tags. > > > > Right, as long as it's fast enough to do > > > > for_each_dirty_page(page, dirty_log) > > for (i = 0; i < host-page-size/16; i += 16) > > append_tag(LDG(page + i)) > > > > to get all the tags for each dirty page. I understood it would be faster > > to use LDGM, but we'd need a new ioctl for that. So I was proposing we > > just piggyback on a new dirty-log ioctl instead. > > That feels a bad idea to me; there's a couple of different ways dirty > page checking work; lets keep extracting the tags separate. > It's sounding like it was a premature optimization anyway. We don't yet know if an ioctl for LDGM is worth it. Looping over LDG may work fine. Thanks, drew _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
