From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44656) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eYg2k-0003yr-En for qemu-devel@nongnu.org; Mon, 08 Jan 2018 17:37:23 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eYg2f-0000ae-Eh for qemu-devel@nongnu.org; Mon, 08 Jan 2018 17:37:22 -0500 Received: from mx1.redhat.com ([209.132.183.28]:52012) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eYg2f-0000aA-5h for qemu-devel@nongnu.org; Mon, 08 Jan 2018 17:37:17 -0500 Date: Mon, 8 Jan 2018 17:37:16 -0500 (EST) From: Paolo Bonzini Message-ID: <242287261.31733448.1515451036017.JavaMail.zimbra@redhat.com> In-Reply-To: <20180108211623.GJ6646@localhost.localdomain> References: <20180108205052.24385-1-vincent@bernat.im> <20180108211623.GJ6646@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] target-i386: add pcid to both Sandy Bridge and Ivy Bridge List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost Cc: Vincent Bernat , Richard Henderson , qemu-devel@nongnu.org ----- Original Message ----- > From: "Eduardo Habkost" > To: "Vincent Bernat" > Cc: "Paolo Bonzini" , "Richard Henderson" , qemu-devel@nongnu.org > Sent: Monday, January 8, 2018 10:16:23 PM > Subject: Re: [PATCH] target-i386: add pcid to both Sandy Bridge and Ivy Bridge > > On Mon, Jan 08, 2018 at 09:50:52PM +0100, Vincent Bernat wrote: > > PCID has been introduced in Sandy Bridge and, currently, KVM doesn't > > object exposing it to VM as long as it is present on the host. Update > > CPU model for both Sandy Bridge and Ivy Bridge accordingly. > > > > Signed-off-by: Vincent Bernat > > Thanks for your patch. > > We need two things, though: > > First, confirming that all hosts where the SandyBridge and > IvyBridge CPU models are runnable will support exposing PCID to > guests (otherwise updating QEMU can make a runnable VM > configuration suddenly stop being runnable). This can happen if > the host kernel is too old. I've been reading it's also Westmere. I'll check more carefully tomorrow. The difference between consumer and server SKUs is important too. > One possible way to work around this problem is to declare that > QEMU 2.12 with KVM will require Linux v3.6 and newer (because we > need Linux kernel commit ad756a1603c5 "KVM: VMX: Implement > PCID/INVPCID for guests with EPT"). Note that PCID is still not supported for guests without EPT, so this would break ept=0 with recent "-cpu" models. I'm not sure of a way to fix it; probably it just has to be documented. Paolo