From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted Date: Tue, 5 Feb 2019 08:24:07 +0100 Message-ID: <20190205072407.GA4311@lst.de> References: <87zhrj8kcp.fsf@morokweng.localdomain> <87womn8inf.fsf@morokweng.localdomain> <20190129134750-mutt-send-email-mst@kernel.org> <6c68f7f7-1b28-6eba-9b8b-2c32efac9701@redhat.com> <20190129213137-mutt-send-email-mst@kernel.org> <20190130074427.GA29516@lst.de> <875ztzxvw2.fsf@morokweng.localdomain> <20190204152416-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190204152416-mutt-send-email-mst@kernel.org> Sender: linux-kernel-owner@vger.kernel.org To: "Michael S. Tsirkin" Cc: Thiago Jung Bauermann , Christoph Hellwig , Jason Wang , virtualization@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, David Gibson , Alexey Kardashevskiy , Paul Mackerras , Benjamin Herrenschmidt , Ram Pai , Jean-Philippe Brucker List-Id: iommu@lists.linux-foundation.org On Mon, Feb 04, 2019 at 04:38:21PM -0500, Michael S. Tsirkin wrote: > It was designed to make, when set, as many guests as we can work > correctly, and it seems to be successful in doing exactly that. > > Unfortunately there could be legacy guests that do work correctly but > become slow. Whether trying to somehow work around that > can paint us into a corner where things again don't > work for some people is a question worth discussing. The other problem is that some qemu machines just throw passthrough devices and virtio devices on the same virtual PCI(e) bus, and have a common IOMMU setup for the whole bus / root port / domain. I think this is completely bogus, but unfortunately it is out in the field. Given that power is one of these examples I suspect that is what Thiago referes to. But in this case the answer can't be that we pile on hack ontop of another, but instead introduce a new qemu machine that separates these clearly, and make that mandatory for the secure guest support.