From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [RFC PATCH] virtio_ring: Use DMA API if guest memory is encrypted Date: Tue, 5 Feb 2019 11:13:39 -0500 Message-ID: <20190205111128-mutt-send-email-mst__20255.0972507865$1549383246$gmane$org@kernel.org> 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> <20190205072407.GA4311@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20190205072407.GA4311@lst.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: Christoph Hellwig Cc: Jean-Philippe Brucker , Benjamin Herrenschmidt , Alexey Kardashevskiy , Ram Pai , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Paul Mackerras , iommu@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, Thiago Jung Bauermann , David Gibson List-Id: virtualization@lists.linuxfoundation.org On Tue, Feb 05, 2019 at 08:24:07AM +0100, Christoph Hellwig wrote: > 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. That could we one approach, assuming one exists that guests already support. -- MST