From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:49573) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aassn-0007WQ-Mo for qemu-devel@nongnu.org; Tue, 01 Mar 2016 17:35:10 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aassk-00076R-I6 for qemu-devel@nongnu.org; Tue, 01 Mar 2016 17:35:09 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41840) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aassk-00075O-DW for qemu-devel@nongnu.org; Tue, 01 Mar 2016 17:35:06 -0500 Date: Wed, 2 Mar 2016 00:35:03 +0200 From: "Michael S. Tsirkin" Message-ID: <20160302001835-mutt-send-email-mst@redhat.com> References: <1456078260-6669-1-git-send-email-davidkiarie4@gmail.com> <20160301134419-mutt-send-email-mst@redhat.com> <56D59DA3.3040002@siemens.com> <56D5A069.9030004@siemens.com> <20160301220139-mutt-send-email-mst@redhat.com> <56D5F8F6.2000001@siemens.com> <20160301223551-mutt-send-email-mst@redhat.com> <56D6086B.3010004@siemens.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <56D6086B.3010004@siemens.com> Subject: Re: [Qemu-devel] [V6 0/4] AMD IOMMU List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: valentine.sinitsyn@gmail.com, marcel@redhat.com, David Kiarie , qemu-devel@nongnu.org On Tue, Mar 01, 2016 at 10:23:55PM +0100, Jan Kiszka wrote: > On 2016-03-01 21:39, Michael S. Tsirkin wrote: > > On Tue, Mar 01, 2016 at 09:17:58PM +0100, Jan Kiszka wrote: > >> On 2016-03-01 21:11, Michael S. Tsirkin wrote: > >>> > >>> What this seems to call for is a new kind of protection > >>> where yes PTE is write protected, but instead of > >>> making PTE writeable (or killing guest) > >>> KVM handles it as an MMIO: emulates the write and then skips the instruction. > >>> > >>> Emulation can be in kernel, just writing into guest memory > >>> on behalf of the guest - with some kind of notifier > >>> to flush the vfio cache - or instead it can exit to userspace > >>> and have QEMU handle it like MMIO and write into guest memory. > >> > >> Exactly, but that's nothing new, is it? It's "just" slow, like other > >> shadow MMUs. > >> > >> Jan > > > > Well AFAIK KVM does not have such an option ATM: MMIO causes exits for > > reads and writes. We want MMIO exits for writes but not reads. > > I agree it should be easy to implement. > > We have read-only memory slot support for quite a while. It's used to > support execute (and read) from emulated ROM devices. > > Jan I didn't realize this causes an mmio exit. > -- > Siemens AG, Corporate Technology, CT RDA ITP SES-DE > Corporate Competence Center Embedded Linux