lkml.org 
[lkml]   [2016]   [Jan]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [Xen-devel] [PATCH v5 09/10] vring: Use the DMA API on Xen
On Sun, Jan 31, 2016 at 12:18 PM, Michael S. Tsirkin <mst@redhat.com> wrote:
> 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 <mst@redhat.com> 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 <luto@kernel.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
>> >
>> > 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.
>

In that case, let me test for real. Can you point me to a git tree
when you have patches 1-8 staged and I'll spin patch 9 v2 and test it
with the real context?

--Andy

\
 
 \ /
  Last update: 2016-01-31 22:01    [W:0.074 / U:0.908 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site