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Re: [Qemu-devel] [RFC PATCH] vfio: VFIO Driver core framework
From: |
Benjamin Herrenschmidt |
Subject: |
Re: [Qemu-devel] [RFC PATCH] vfio: VFIO Driver core framework |
Date: |
Tue, 15 Nov 2011 11:49:29 +1100 |
On Tue, 2011-11-15 at 11:05 +1100, David Gibson wrote:
> Being strict, or at least enforcing strictness, requires that the
> infrastructure track all the maps, so that the unmaps can be
> matching. This is not a natural thing with the data structures you
> want for all IOMMUs. For example on POWER, the IOMMU (aka TCE table)
> is a simple 1-level pagetable. One pointer with a couple of
> permission bits per IOMMU page. Handling oddly overlapping operations
> on that data structure is natural, enforcing strict matching of maps
> and unmaps is not and would require extra information to be stored by
> vfio. On POWER, the IOMMU operations often *are* a hot path, so
> manipulating those structures would have a real cost, too.
In fact they are a very hot path even. There's no way we can afford the
cost of tracking per page mapping/unmapping (other than bumping the page
count on a page that's currently mapped or via some debug-only feature).
Cheers,
Ben.
Re: [Qemu-devel] [RFC PATCH] vfio: VFIO Driver core framework, Konrad Rzeszutek Wilk, 2011/11/11
Re: [Qemu-devel] [RFC PATCH] vfio: VFIO Driver core framework, Scott Wood, 2011/11/16
Re: [Qemu-devel] [RFC PATCH] vfio: VFIO Driver core framework, Alex Williamson, 2011/11/17
Re: [Qemu-devel] [RFC PATCH] vfio: VFIO Driver core framework, Scott Wood, 2011/11/11