From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42273) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YqJqy-00033n-4a for qemu-devel@nongnu.org; Thu, 07 May 2015 07:20:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YqJqt-0004ok-A1 for qemu-devel@nongnu.org; Thu, 07 May 2015 07:20:32 -0400 Received: from mail-la0-f43.google.com ([209.85.215.43]:35522) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YqJqt-0004oY-3W for qemu-devel@nongnu.org; Thu, 07 May 2015 07:20:27 -0400 Received: by labbd9 with SMTP id bd9so28103121lab.2 for ; Thu, 07 May 2015 04:20:26 -0700 (PDT) Date: Thu, 7 May 2015 13:20:27 +0200 From: Christoffer Dall Message-ID: <20150507112027.GC25885@cbox> References: <1430817191-6231-1-git-send-email-j.fanguede@virtualopensystems.com> <20150506141249.GA6796@cbox> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Subject: Re: [Qemu-devel] [RFC] ARM/ARM64: KVM: Implement KVM_FLUSH_DCACHE_GPA ioctl List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?iso-8859-1?B?Suly6W15IEZhbmd16GRl?= Cc: "open list:Overall" , QEMU Developers , Paolo Bonzini , VirtualOpenSystems Technical Team , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org On Thu, May 07, 2015 at 12:50:50PM +0200, Jérémy Fanguède wrote: > On Wed, May 6, 2015 at 4:12 PM, Christoffer Dall > wrote: > > Hi Jérémy, > > > > On Tue, May 05, 2015 at 11:13:11AM +0200, Jérémy Fanguède wrote: > >> To maintain cache coherency on ARM, we may need a mechanism to flush > >> the data cache. > > > > In addition to generally just making this functionality available (see > > below), do you have an actual use case in mind for this? To solve the > > VGA issue, for example, we already have a patch series from Drew trying > > to address this. Does that not work for you? > > > > There was a long discussion about this here: > > https://lists.cs.columbia.edu/pipermail/kvmarm/2015-February/013593.html > > > > Drew then created a patch set, here: > > https://lists.nongnu.org/archive/html/qemu-devel/2015-03/msg01254.html > > > > and replied to himself, here: > > https://www.marc.info/?l=android-virt&m=142670523929132&w=3 > > > > Which basically says that he doesn't like having to do flushes all over > > QEMU (IIUC), so he sent this version instead: > > https://lists.cs.columbia.edu/pipermail/kvmarm/2015-March/014027.html > > > > Which he now said he'd respin. > > In fact, I used this ioctl in pairs with this QEMU patch series: > https://lists.nongnu.org/archive/html/qemu-devel/2015-05/msg00407.html > My current work doesn't do anything about vga ram, so vga issue > probably still persists, but it solves others issues with some > emulated devices (mainly PCI) which were failing before and now work > fine with this patch. Why does Drew's approach not work and your approach works here? What is the case that we haven't though about yet? -Christoffer