On 12/2/20 5:17 AM, Ankur Arora wrote: > On 2020-12-01 5:26 p.m., David Woodhouse wrote >> On Tue, 2020-12-01 at 16:40 -0800, Ankur Arora wrote: >>> On 2020-12-01 5:07 a.m., David Woodhouse wrote: [...] >>>> If that was allowed, wouldn't it have been a much simpler fix for >>>> CVE-2019-3016? What am I missing? >>> >>> Agreed. >>> >>> Perhaps, Paolo can chime in with why KVM never uses pinned page >>> and always prefers to do cached mappings instead? >>> >>>> >>>> Should I rework these to use kvm_write_guest_cached()? >>> >>> kvm_vcpu_map() would be better. The event channel logic does RMW operations >>> on shared_info->vcpu_info. >> >> I've ported the shared_info/vcpu_info parts and made a test case, and >> was going back through to make it use kvm_write_guest_cached(). But I >> should probably plug on through the evtchn bits before I do that. >> >> I also don't see much locking on the cache, and can't convince myself >> that accessing the shared_info page from multiple CPUs with >> kvm_write_guest_cached() or kvm_map_gfn() is sane unless they each have >> their own cache. > > I think you could get a VCPU specific cache with kvm_vcpu_map(). > steal clock handling creates such a mapping cache (struct gfn_to_pfn_cache). Joao
