linux-kernel - Re: [PATCH] virtio-net: Read MAC only after initializing MSI-X

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Date:	Tue, 16 Aug 2011 01:17:07 +0300
From:	Sasha Levin <levinsasha928@...il.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	linux-kernel@...r.kernel.org,
	"Michael S. Tsirkin" <mst@...hat.com>,
	virtualization@...ts.linux-foundation.org, netdev@...r.kernel.org,
	kvm@...r.kernel.org
Subject: Re: [PATCH] virtio-net: Read MAC only after initializing MSI-X

On Mon, 2011-08-15 at 09:55 +0930, Rusty Russell wrote:
> On Sun, 14 Aug 2011 16:57:32 +0300, Sasha Levin <levinsasha928@...il.com> wrote:
> > On Sun, 2011-08-14 at 12:23 +0930, Rusty Russell wrote:
> > > On Sat, 13 Aug 2011 11:51:01 +0300, Sasha Levin <levinsasha928@...il.com> wrote:
> > > > The MAC of a virtio-net device is located at the first field of the device
> > > > specific header. This header is located at offset 20 if the device doesn't
> > > > support MSI-X or offset 24 if it does.
> > > 
> > > Erk.  This means, in general, we have to do virtio_find_single_vq or
> > > config->find_vqs before we examine any config options.
> > > 
> > > Look at virtio_blk, which has the same error.
> > > 
> > > Solutions in order of best to worst:
> > > (1) Enable MSI-X before calling device probe.  This means reserving two
> > >     vectors in virtio_pci_probe to ensure we *can* do this, I think.  Michael?
> > 
> > Do you mean reserving the vectors even before we probed the device for
> > MSI-X support? Wouldn't we need 3 vectors then? (config, input, output).
> 
> We want three, but *need* two: see vp_find_vqs().  Also, the generic
> code doesn't know how many virtqueues we have on the device.

We can just pci_enable_msix() and see if we can get 2 vectors, if we can
- we assume the device has msix on, right?


-- 

Sasha.

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