On Wed, 2008-12-03 at 08:35 +1030, Rusty Russell wrote:
> On Wednesday 03 December 2008 05:38:21 Hollis Blanchard wrote:
> > I just spent a number of hours tracking this one down, and I'm not too
> > thrilled about it. vp_find_vq() does the memory allocation for virtio
> > PCI rings, and it uses kzalloc() to do it. This is bad because the ring
> > memory *must* be page-aligned.
> >
> > According to Anthony, at the time this code was written, various slab
> > allocators were checked and all happened to return page-aligned buffers.
> > So how did I hit a problem? I had enabled CONFIG_SLUB_DEBUG_ON while
> > investigating an unrelated problem, which offset the address by 64
> > bytes.
> >
> > One option is to add a BUG_ON(addr & ~PAGE_MASK) to vp_find_vq(). That's
> > better than nothing, but still stinks.
>
> It's a bug, we fix it. I've complained before, but since there was no
> evidence of it actually breaking, I didn't push.
>
> Prepare a patch, I'll try to get it in this release.
virtio: ring queues must be page-aligned
kzalloc() does not guarantee page alignment, and in fact this broke when
I enabled CONFIG_SLUB_DEBUG_ON.
Signed-off-by: Hollis Blanchard <[EMAIL PROTECTED]>
---
Tested with virtio-blk root filesystem.
diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -237,7 +237,8 @@ static struct virtqueue *vp_find_vq(stru
info->queue_index = index;
info->num = num;
- info->queue = kzalloc(PAGE_ALIGN(vring_size(num)), GFP_KERNEL);
+ info->queue = alloc_pages_exact(PAGE_ALIGN(vring_size(num)),
+ GFP_KERNEL|__GFP_ZERO);
if (info->queue == NULL) {
err = -ENOMEM;
goto out_info;
--
Hollis Blanchard
IBM Linux Technology Center
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