From: Will Deacon Subject: Re: [RFC 0/2] arm-smmu-v3 tlbi-on-map option Date: Wed, 12 Jul 2017 18:54:56 +0100 Message-ID: <20170712175454.GF15191@arm.com> References: <1499613303-30173-1-git-send-email-eric.auger@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1499613303-30173-1-git-send-email-eric.auger-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Eric Auger Cc: mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Marc.Zyngier-5wv7dgnIgG8@public.gmane.org, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, christoffer.dall-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, eric.auger.pro-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org List-Id: iommu@lists.linux-foundation.org Hi Eric, On Sun, Jul 09, 2017 at 05:15:01PM +0200, Eric Auger wrote: > This series adds a new tlbi-on-map option to the smmuv3 driver. > When set, the IO_PGTABLE_QUIRK_TLBI_ON_MAP quirk is applied for > LPAE tables and the smmuv3 driver sends TLB invalidations on map. > > This mode is useful when running the driver on a guest as it allows > the virtualizer to trap any change to the translation structures. > This is similar to the Intel vtd caching mode (CM). > > This is especially needed for VFIO integration integration where > guest mappings must be applied to the physical IOMMU. > > At the moment the option only is available for DT probing. I'm really not a fan of this approach. If a virtual IOMMU implementation is advertising itself as an SMMUv3, then it should adhere to the SMMUv3 architecture and not require non-standard behaviour from the driver. If we're going to allow that, then we're better off going the extra mile and using a PV approach. Given that the the SMMU3 architecture does *not* require TLBI on map, then I don't think we should be quirking our behaviour in this way. The fact that you only have this implemented for DT is the canary in the coal mine imo. Will