On Tue, Jan 30, 2018 at 01:20:52AM +0000, David Dunn wrote: > Eduardo, > > This is why it would be good to have a CPUID bit that says: > "apply SkyLake RSB stuffing." That's preferable to "trust FMS" > for VMware. Agreed it would be more useful than "trust FMS". However, I believe a "no need to apply Skylake RSB stuffing" bit (which I called "we promise we won't migrate to Skylake" previously) would allow guests to enable safer behavior by default under older hypervisors that don't support this bit. > > If Intel defines such a feature flag, sets it on SkyLake, and > Linux uses it... that would be very helpful for VMware. > > I won't speak for GCE and AWS. But hopefully they can indicate > whether it would help them as well. I agree that having a standard flag on the CPUID space to specify that would be very helpful. > > If Intel cannot define/implement such a flag on SkyLake, then > maybe the engineers on this email could define a flag in the > hypervisor specific CPUID space. Linux would need to query > that flag if it sees CPUID[1].ECX[31] set. That's not as nice > since it makes detection on bare metal and virtualization > platforms different, but it better than keying off FMS. Agreed. -- Eduardo
