From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51712) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YJ2Tv-0006w7-5h for qemu-devel@nongnu.org; Wed, 04 Feb 2015 11:07:16 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YJ2Tp-0004X6-O9 for qemu-devel@nongnu.org; Wed, 04 Feb 2015 11:07:11 -0500 Received: from mx1.redhat.com ([209.132.183.28]:57864) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YJ2Tp-0004Wx-Fe for qemu-devel@nongnu.org; Wed, 04 Feb 2015 11:07:05 -0500 Received: from int-mx10.intmail.prod.int.phx2.redhat.com (int-mx10.intmail.prod.int.phx2.redhat.com [10.5.11.23]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id t14G73rX003434 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL) for ; Wed, 4 Feb 2015 11:07:04 -0500 Date: Wed, 4 Feb 2015 17:07:02 +0100 From: "Michael S. Tsirkin" Message-ID: <20150204160702.GA22311@redhat.com> References: <1418745044-3986-1-git-send-email-ghammer@redhat.com> <1418745044-3986-3-git-send-email-ghammer@redhat.com> <20150122145246.5d020fab@nial.brq.redhat.com> <54CE227A.9020000@redhat.com> <20150202134635.434233f7@nial.brq.redhat.com> <54CF7803.7020906@redhat.com> <20150202145502.72dd11cd@nial.brq.redhat.com> <1894120274.5221719.1423062578928.JavaMail.zimbra@redhat.com> <20150204165354.5e7106c5@nial.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150204165354.5e7106c5@nial.brq.redhat.com> Subject: Re: [Qemu-devel] [PATCH V11 2/3] i386: Add a Virtual Machine Generation ID device List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Igor Mammedov Cc: Gal Hammer , qemu-devel@nongnu.org On Wed, Feb 04, 2015 at 04:53:54PM +0100, Igor Mammedov wrote: > > > > Isn't this will cause a VMEXIT when the guest is reading the GUID? If it > > > > is then this idea was already presented and Michael didn't approve it. > > > It will, but is it performance critical? VM supposed to read it > > > at start-up and on getting notification. So I think VMEXIT in this case > > > is not sufficient to drop simple and strait-forward design. > > > > I agree with you on that and one of the previous patches did used a fixed-address to store the GUID while read/write access were handled by qemu driver code. But as I wrote before, it was Michael who didn't approved it so I proposed this method although it is a bit more complicated. > > > > I don't know how to break out of this dead-lock... :( > Could you post a link to driver based version of series. > Perhaps we could address Michael's comments and still stay > with a simple implementation. The point is to keep all allocations in guest. I don't want to "steal" a page from guest. > > > > > > > > BTW: > > > For start-up fw_cfg file is not any way better, it's also causes VMEXIT > > > for every byte it reads from it. > > > > I don't understand your claim. Accessing the fw_cfg "file" doesn't cause VMEXIT as it located somewhere in the guest's memory range. > As far as I'm aware MMIO or ioport is used for reading fw_cfg contents > on guest side, one byte at a time and every such access causes VMEXIT > into QEMU callback. It's highly unlikely to be measureable. Prove me wrong if you like. -- MST