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Message-ID: <56AB4053.4070007@citrix.com>
Date: Fri, 29 Jan 2016 10:34:59 +0000
From: David Vrabel <david.vrabel@...rix.com>
To: Andy Lutomirski <luto@...nel.org>,
"Michael S. Tsirkin" <mst@...hat.com>
CC: Cornelia Huck <cornelia.huck@...ibm.com>,
Joerg Roedel <jroedel@...e.de>, KVM <kvm@...r.kernel.org>,
linux-s390 <linux-s390@...r.kernel.org>,
"Benjamin Herrenschmidt" <benh@...nel.crashing.org>,
Stefano Stabellini <stefano.stabellini@...citrix.com>,
Sebastian Ott <sebott@...ux.vnet.ibm.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Christoph Hellwig <hch@....de>,
"Christian Borntraeger" <borntraeger@...ibm.com>,
David Vrabel <david.vrabel@...rix.com>,
<xen-devel@...ts.xenproject.org>, <sparclinux@...r.kernel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Linux Virtualization <virtualization@...ts.linux-foundation.org>,
David Woodhouse <dwmw2@...radead.org>,
"David S. Miller" <davem@...emloft.net>,
"Martin Schwidefsky" <schwidefsky@...ibm.com>
Subject: Re: [Xen-devel] [PATCH v5 09/10] vring: Use the DMA API on Xen
On 29/01/16 02:31, Andy Lutomirski wrote:
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
> 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
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