> -----Original Message----- > From: Marcelo Tosatti [mailto:[email protected]] > Sent: Tuesday, May 15, 2012 10:20 AM > To: Mao, Junjie > Cc: Eric Northup; [email protected] > Subject: Re: [PATCH] KVM: x86: Implement PCID/INVPCID for guests with EPT > > On Mon, May 14, 2012 at 07:15:18AM +0000, Mao, Junjie wrote: > > > On Wed, May 9, 2012 at 5:32 PM, Mao, Junjie <[email protected]> > wrote: > > > > This patch handles PCID/INVPCID for guests. > > > > > > > > Process-context identifiers (PCIDs) are a facility by which a logical > processor may cache information for multiple linear-address spaces so that the > processor may retain cached information when software switches to a > different linear-address space. Refer to section 4.10.1 in IA32 Intel Software > Developer's Manual Volume 3A for details. > > > > > > > > For guests with EPT, the PCID feature is enabled and INVPCID behaves as > running natively. > > > > For guests without EPT, the PCID feature is disabled and INVPCID > > > > triggers > #UD. > > > > > > > Do I understand correctly that this means it is impossible to migrate a > guest which is using PCID from a host with EPT to a host without EPT (by > passing enable_ept=0 to the module, for example) ? > > > > I think you are right. Guests using PCID/INVPCID cannot migrate to a host > without it, and EPT is a precondition of this feature. > > Are there processors that support PCI/INVPCID for the host but lack support > for SECONDARY_EXEC_ENABLE_INVPCID?
There're some with PCID but without INVPCID. For those processors support INVPCID, SECONDARY_EXEC_ENABLE_INVPCID support should be present. As PCID has little benefits without INVPCID, these two features are exposed/hidden as a whole. > > > > Does the emulated CR3 load need to learn about the new function of the > low bits? > > > > I have not found any restrictions on writing CR3 brings about by PCID. > > It would be good for completeness. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
