From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52217) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b8SF5-0003it-0i for qemu-devel@nongnu.org; Thu, 02 Jun 2016 09:00:56 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b8SF0-0005Ie-1q for qemu-devel@nongnu.org; Thu, 02 Jun 2016 09:00:55 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54787) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b8SEz-0005Ia-Ro for qemu-devel@nongnu.org; Thu, 02 Jun 2016 09:00:49 -0400 Date: Thu, 2 Jun 2016 07:00:46 -0600 From: Alex Williamson Message-ID: <20160602070046.761be49c@ul30vt.home> In-Reply-To: <20160602084439.GB3477@pxdev.xzpeter.org> References: <1463847590-22782-1-git-send-email-bd.aviv@gmail.com> <1463847590-22782-2-git-send-email-bd.aviv@gmail.com> <57408FDB.1010000@web.de> <20160602084439.GB3477@pxdev.xzpeter.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v3 1/3] IOMMU: add VTD_CAP_CM to vIOMMU capability exposed to guest List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Peter Xu Cc: Jan Kiszka , "Aviv B.D" , qemu-devel@nongnu.org, "Michael S. Tsirkin" On Thu, 2 Jun 2016 16:44:39 +0800 Peter Xu wrote: > On Sat, May 21, 2016 at 06:42:03PM +0200, Jan Kiszka wrote: > > On 2016-05-21 18:19, Aviv B.D wrote: > > > From: "Aviv Ben-David" > > > > > > This flag tells the guest to invalidate tlb cache also after unmap operations. > > > > > > Signed-off-by: Aviv Ben-David > > > --- > > > hw/i386/intel_iommu.c | 3 ++- > > > hw/i386/intel_iommu_internal.h | 1 + > > > 2 files changed, 3 insertions(+), 1 deletion(-) > > > > > > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c > > > index 347718f..1af8da8 100644 > > > --- a/hw/i386/intel_iommu.c > > > +++ b/hw/i386/intel_iommu.c > > > @@ -1949,7 +1949,8 @@ static void vtd_init(IntelIOMMUState *s) > > > s->iq_last_desc_type = VTD_INV_DESC_NONE; > > > s->next_frcd_reg = 0; > > > s->cap = VTD_CAP_FRO | VTD_CAP_NFR | VTD_CAP_ND | VTD_CAP_MGAW | > > > - VTD_CAP_SAGAW | VTD_CAP_MAMV | VTD_CAP_PSI | VTD_CAP_SLLPS; > > > + VTD_CAP_SAGAW | VTD_CAP_MAMV | VTD_CAP_PSI | VTD_CAP_SLLPS | > > > + VTD_CAP_CM; > > > > Again, needs to be optional because not all guests will support it or > > behave differently when it's set (I've one that refuses to work). > > There should be more than one way to make it optional. Which is > better? What I can think of: > > (Assume we have Marcel's "-device intel_iommu" working already) > > 1. Let the CM bit optional, or say, we need to specify something like > "-device intel_iommu,cmbit=on" or we will disable CM bit. If we > have CM disabled but with VFIO device, let QEMU raise error. > > 2. We automatically detect whether we need CM bit. E.g., if we have > VFIO and vIOMMU both enabled, we automatically set the bit. Another > case is maybe we would in the future support nested vIOMMU? If so, > we can do the same thing for the nested feature. Why do we need to support VT-d for guests that do not support CM=1? The VT-d spec indicates that software should be written to handle both caching modes (6.1). Granted this is a *should* and not a *must*, but can't we consider guests that do not support CM=1 incompatible with emulated VT-d? If CM=0 needs to be supported then we need to shadow all of the remapping structures since vfio effectively becomes a cache of the that would otherwise depend on the invalidation of both present and non-present entries. What guests do not support CM=1? Thanks, Alex