From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 41jH1h3f1zzF3GD for ; Sat, 4 Aug 2018 18:21:28 +1000 (AEST) Date: Sat, 4 Aug 2018 01:21:20 -0700 From: Christoph Hellwig To: Benjamin Herrenschmidt Cc: Christoph Hellwig , "Michael S. Tsirkin" , Will Deacon , Anshuman Khandual , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, aik@ozlabs.ru, robh@kernel.org, joe@perches.com, elfring@users.sourceforge.net, david@gibson.dropbear.id.au, jasowang@redhat.com, mpe@ellerman.id.au, linuxram@us.ibm.com, haren@linux.vnet.ibm.com, paulus@samba.org, srikar@linux.vnet.ibm.com, robin.murphy@arm.com, jean-philippe.brucker@arm.com, marc.zyngier@arm.com Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices Message-ID: <20180804082120.GB4421@infradead.org> References: <20180802182959-mutt-send-email-mst@kernel.org> <82ccef6ec3d95ee43f3990a4a2d0aea87eb45e89.camel@kernel.crashing.org> <20180802200646-mutt-send-email-mst@kernel.org> <20180802225738-mutt-send-email-mst@kernel.org> <20180803070507.GA1344@infradead.org> <20180803160246.GA13794@infradead.org> <22310f58605169fe9de83abf78b59f593ff7fbb7.camel@kernel.crashing.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <22310f58605169fe9de83abf78b59f593ff7fbb7.camel@kernel.crashing.org> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, Aug 03, 2018 at 01:58:46PM -0500, Benjamin Herrenschmidt wrote: > You are saying something along the lines of "I don't like an > instruction in your ISA, let's not support your entire CPU architecture > in Linux". No. I'm saying if you can't describe your architecture in the virtio spec document it is bogus. > Our setup is not fucked. It makes a LOT of sense and it's a very > sensible design. It's hitting a problem due to a corner case oddity in > virtio bypassing the MMU, we've worked around such corner cases many > times in the past without any problem, I fail to see what the problem > is here. No matter if you like it or not (I don't!) virtio is defined to bypass dma translations, it is very clearly stated in the spec. It has some ill-defined bits to bypass it, so if you want the dma mapping API to be used you'll have to set that bit (in its original form, a refined form, or an entirely newly defined sane form) and make sure your hypersivors always sets it. It's not rocket science, just a little bit for work to make sure your setup is actually going to work reliably and portably. > We aren't going to cancel years of HW and SW development for our Maybe you should have actually read the specs you are claiming to implemented before spending all that effort.