On 10/29/2012 09:44 PM, Jeremy Fitzhardinge wrote: > On 10/29/2012 07:45 AM, Glauber Costa wrote: >> On 10/24/2012 05:13 PM, Marcelo Tosatti wrote: >>> Allow a guest to register a second location for the VCPU time info >>> >>> structure for each vcpu (as described by MSR_KVM_SYSTEM_TIME_NEW). >>> This is intended to allow the guest kernel to map this information >>> into a usermode accessible page, so that usermode can efficiently >>> calculate system time from the TSC without having to make a syscall. >>> >>> Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx> >> Can you please be a bit more specific about why we need this? Why does >> the host need to provide us with two pages with the exact same data? Why >> can't just do it with mapping tricks in the guest? > > In Xen the pvclock structure is embedded within a pile of other stuff > that shouldn't be mapped into guest memory, so providing for a second > location allows it to be placed whereever is convenient for the guest. > That's a restriction of the Xen ABI, but I don't know if it affects KVM. > > J > In kvm the exported data seems to be exactly the same. So it makes sense to have a single page exported to the guest. The guest may have a facility that maps the vsyscall clock and the normal clock to a specific location given a page - that can be either a different page or the same page. Any reason why it wouldn't work? -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
