linux-kernel - Re: [PATCH v3 0/3] virtio DMA API core stuff

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Date:	Wed, 28 Oct 2015 00:09:54 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Andy Lutomirski <luto@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Joerg Roedel <jroedel@...e.de>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Christoph Hellwig <hch@....de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	KVM <kvm@...r.kernel.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-s390 <linux-s390@...r.kernel.org>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH v3 0/3] virtio DMA API core stuff

On Tue, Oct 27, 2015 at 11:53 PM, David Woodhouse <dwmw2@...radead.org> wrote:
> On Tue, 2015-10-27 at 23:38 -0700, Andy Lutomirski wrote:
>>
>> Changes from v2:
>>  - Fix really embarrassing bug.  This version actually works.
>
> So embarrassing you didn't want to tell us what it was? ...

Shhh, it's a secret!

I somehow managed to test-boot a different kernel than I thought I was booting.

>
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -292,7 +292,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
>                         vq, desc, total_sg * sizeof(struct vring_desc),
>                         DMA_TO_DEVICE);
>
> -               if (vring_mapping_error(vq, vq->vring.desc[head].addr))
> +               if (vring_mapping_error(vq, addr))
>                         goto unmap_release;
>
>                 vq->vring.desc[head].flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_INDIRECT);
>
> That wasn't going to be the reason for Christian's failure, was it?
>

Not obviously, but it's possible.  Now that I'm staring at it, I have
some more big-endian issues, so there'll be a v4.  I'll also play with
Michael's thing.  Expect a long delay, though -- my flight's about to
leave.

The readme notwithstanding, virtme (https://github.com/amluto/virtme)
actually has s390x support, so I can try to debug when I get home.
I'm not about to try doing this on a laptop :)

--Andy
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