From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH] KVM: x86: Implement PCID/INVPCID for guests with EPT Date: Mon, 14 May 2012 23:20:14 -0300 Message-ID: <20120515022014.GA16859@amt.cnet> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Eric Northup , "kvm@vger.kernel.org" To: "Mao, Junjie" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:4758 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965177Ab2EOCsy (ORCPT ); Mon, 14 May 2012 22:48:54 -0400 Content-Disposition: inline In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On Mon, May 14, 2012 at 07:15:18AM +0000, Mao, Junjie wrote: > > On Wed, May 9, 2012 at 5:32 PM, Mao, Junjie 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? > > 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.