From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [Xen-devel] [PATCH v5 09/10] vring: Use the DMA API on Xen Date: Sun, 31 Jan 2016 22:18:17 +0200 Message-ID: <20160131221600-mutt-send-email-mst@redhat.com> References: <64e979cc139c5e6a9bbfae9f1bc5e6693d91bea9.1454034075.git.luto@kernel.org> <56AB4053.4070007@citrix.com> <20160131220601-mutt-send-email-mst@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: 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: Andy Lutomirski Cc: linux-s390 , sparclinux@vger.kernel.org, Joerg Roedel , KVM , Stefano Stabellini , Benjamin Herrenschmidt , Sebastian Ott , "linux-kernel@vger.kernel.org" , Linux Virtualization , Christian Borntraeger , "David S. Miller" , David Vrabel , Andy Lutomirski , Paolo Bonzini , "xen-devel@lists.xenproject.org" , David Woodhouse , Christoph Hellwig , Martin Schwidefsky List-Id: virtualization@lists.linuxfoundation.org On Sun, Jan 31, 2016 at 12:13:58PM -0800, Andy Lutomirski wrote: > On Sun, Jan 31, 2016 at 12:09 PM, Michael S. Tsirkin wrote: > > On Fri, Jan 29, 2016 at 10:34:59AM +0000, David Vrabel wrote: > >> On 29/01/16 02:31, Andy Lutomirski wrote: > >> > Signed-off-by: Andy Lutomirski > >> > --- > >> > drivers/virtio/virtio_ring.c | 12 ++++++++++++ > >> > 1 file changed, 12 insertions(+) > >> > > >> > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > >> > index c169c6444637..305c05cc249a 100644 > >> > --- a/drivers/virtio/virtio_ring.c > >> > +++ b/drivers/virtio/virtio_ring.c > >> > @@ -47,6 +47,18 @@ > >> > > >> > static bool vring_use_dma_api(void) > >> > { > >> > +#if defined(CONFIG_X86) && defined(CONFIG_XEN) > >> > + /* > >> > + * In theory, it's possible to have a buggy QEMU-supposed > >> > + * emulated Q35 IOMMU and Xen enabled at the same time. On > >> > + * such a configuration, virtio has never worked and will > >> > + * not work without an even larger kludge. Instead, enable > >> > + * the DMA API if we're a Xen guest, which at least allows > >> > + * all of the sensible Xen configurations to work correctly. > >> > + */ > >> > + return static_cpu_has(X86_FEATURE_XENPV); > >> > >> You want: > >> > >> if (xen_domain()) > >> return true; > >> > >> Without the #if so we use the DMA API for all types of Xen guest on all > >> architectures. > >> > >> David > > > > I doubt HVM domains can have virtio devices. > > > > They certainly can under nested virt (L0 provides virtio device, L1 is > Xen, and L2 is Linux). Of course, this won't work given the current > QEMU situation unless Xen can pass things through to dom0 without an > IOMMU, which seems plausible to me. > > But yes, xen_domain() sounds right to me. I just failed to find that > function when I wrote this patch. > > Michael, if you like the rest of the series, I'd be okay if you > changed this patch to use xen_domain() when you apply it. If I send a > v2, I'll fix it up. > > --Andy I'd rather you just posted a tested v2 of 9/10 for now as I don't test Xen. It seems easy but I had more than my share of obvious fixes failing spectacularly. -- MST