linux-kernel - Re: [PATCH V2] VFIO driver: Non-privileged user level PCI drivers

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Date:	Wed, 30 Jun 2010 22:16:23 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Tom Lyon <pugs@...co.com>
Cc:	randy.dunlap@...cle.com, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, chrisw@...s-sol.org, joro@...tes.org,
	hjk@...utronix.de, mst@...hat.com, avi@...hat.com, gregkh@...e.de,
	aafabbri@...co.com, scofeldm@...co.com
Subject: Re: [PATCH V2] VFIO driver: Non-privileged user level PCI drivers

On Tue, 2010-06-08 at 14:21 -0700, Tom Lyon wrote:
> +int vfio_dma_unmap_dm(struct vfio_listener *listener, struct vfio_dma_map *dmp)
> +{
> +	unsigned long start, npage;
> +	struct dma_map_page *mlp;
> +	struct list_head *pos, *pos2;
> +	int ret;
> +
> +	start = dmp->vaddr & ~PAGE_SIZE;
> +	npage = dmp->size >> PAGE_SHIFT;
> +
> +	ret = -ENXIO;
> +	mutex_lock(&listener->vdev->dgate);
> +	list_for_each_safe(pos, pos2, &listener->dm_list) {
> +		mlp = list_entry(pos, struct dma_map_page, list);
> +		if (dmp->vaddr != mlp->vaddr || mlp->npage != npage)
> +			continue;
> +		ret = 0;
> +		vfio_dma_unmap(listener, mlp);
> +		break;
> +	}

Hi Tom,

Shouldn't we be matching the mlp based on daddr instead of vaddr?  We
can have multiple dma address pointing at the same virtual address, so
dma address is the unique element.  I'm also nervous about this dm_list.
For qemu device assignment, we're potentially statically mapping many GB
of iova space.  It seems like this could get incredibly bloated and
slow.  Thanks,

Alex

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