From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoffer Dall Subject: Re: [RFC] ARM/ARM64: KVM: Implement KVM_FLUSH_DCACHE_GPA ioctl Date: Thu, 7 May 2015 13:20:27 +0200 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-Transfer-Encoding: QUOTED-PRINTABLE Cc: kvmarm@lists.cs.columbia.edu, Paolo Bonzini , linux-arm-kernel@lists.infradead.org, "open list:Overall" , QEMU Developers , VirtualOpenSystems Technical Team To: =?iso-8859-1?B?Suly6W15IEZhbmd16GRl?= Return-path: Received: from mail-lb0-f173.google.com ([209.85.217.173]:35171 "EHLO mail-lb0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750806AbbEGLU1 (ORCPT ); Thu, 7 May 2015 07:20:27 -0400 Received: by lbbuc2 with SMTP id uc2so28388506lbb.2 for ; Thu, 07 May 2015 04:20:26 -0700 (PDT) Content-Disposition: inline In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: On Thu, May 07, 2015 at 12:50:50PM +0200, J=E9r=E9my Fangu=E8de wrote: > On Wed, May 6, 2015 at 4:12 PM, Christoffer Dall > wrote: > > Hi J=E9r=E9my, > > > > On Tue, May 05, 2015 at 11:13:11AM +0200, J=E9r=E9my Fangu=E8de wro= te: > >> To maintain cache coherency on ARM, we may need a mechanism to flu= sh > >> 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 tr= ying > > 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= =2Ehtml > > > > Drew then created a patch set, here: > > https://lists.nongnu.org/archive/html/qemu-devel/2015-03/msg01254.h= tml > > > > and replied to himself, here: > > https://www.marc.info/?l=3Dandroid-virt&m=3D142670523929132&w=3D3 > > > > 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.ht= ml > > > > Which he now said he'd respin. >=20 > In fact, I used this ioctl in pairs with this QEMU patch series: > https://lists.nongnu.org/archive/html/qemu-devel/2015-05/msg00407.htm= l > 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 i= s the case that we haven't though about yet? -Christoffer