On Wed, May 23, 2012 at 05:02:28AM +0000, Mao, Junjie wrote: > > > > > > The previous patch regards PCID and INVPCID as a whole because qemu > > doesn't support cpuid leaf 7 configuration at present. This is not the case > > in this > > version. > > > > The problem with cpu_has_hypervisor check is that its Linux specific. > > > > Any solution should also take into account other OSes running as L1 > > > > guest and virtualizing L2 guest. > > > > > > Is there any other way, which applies to all host hypervisors, to know if > > > kvm is > > running as a guest hypervisor? > > > > The point is that other hypervisor might be running as L1 guest. > > > > The problem with enabling PCID for the L2 guest is that it can share same > > PCID > > values with the L1 hypervisor. > > > > However, if the L1 hypervisor enables and configures VPID (given that > > the L0 hypervisor emulates and exposes it), there is no problem in enabling > > PCID for both L1 and L2 guests because TLB entries will be differentiated by > > their VPID values, even if their PCID values are the same. > > > > This may not be a problem because: > > 1. If both L1 and L2 use VPID, there's no problem as you have mentioned. > 2. If neither L1 and L2 use VPID, the TLB entries are all tagged with VPID 0 > and any VM entries or exits will invalidate them. > 3. If one of L1 and L2 uses VPID but the other don't, the TLB entries still > have different VPID and won't affect each other. > > I haven't thought over exposing PCID to L2 guests before but it seems that no > problem exists in exposing PCID to L2 guests. Is it looks ok to you if PCID > is always exposed, no matter for L1 or L2 guests?
Yes, it appears to be OK, because of the TLB flush on vm-entry/vm-exit without VPID (2 above). Avi ? > > So i think that checking whether EPT _and_ VPID are supported should be a > > precondition to enable PCID support for guests. > > > > Should this check be carried out on L0 too? If so, this will add one more > dependency of PCID on VPID, which doesn't exist in the manual. Actually it is not necessary because L0 cannot access data which is EPT-tagged (and you already require EPT). So it is fine to remove the cpu_has_hypervisor check along with vmx_pcid_supported(). -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
