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Re: Problems with UVM pagefaults

On Thu, Jan 10, 2013 at 05:41:38PM +0100, Roger Pau Monné wrote:
> [...]
> That's how is done in Linux, and that was my first attempt to implement
> this device under NetBSD. However, I've also found problems with this
> implementation. In d_mmap you have to return physical addresses, the
> problem with that is that Xen has physical addresses and machine
> addresses, and there's a mapping between physical and machine addresses
> (physical addresses are used as a translation to machine addresses, so
> the OS thinks memory is contiguous, when it is not).
> When returning physical addresses from the d_mmap handler I've found
> that the memory system extracts the machine address behind that physical
> address and tries to assign that machine address to a VA in the calling
> process virtual memory. This did not work, because the machine address
> behind the physical address returned in the handler doesn't belong to
> the same domain, so trying to map this to a different VA in userspace is
> not allowed (Xen only allows this by using a set of specific hypercalls,
> as you can see in gntmap_grant_ref).

Can't your ioctl work in the same way as IOCTL_PRIVCMD_MMAP ?
Reading quickly the code, I think this one works with machine adresses and
its onw fault handler, and doesn't deal with physical addresses at all.
I think this is what you need.

Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference

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