Re: X server in dom0: Bad VBT signature

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Mon, Sep 03, 2012 at 07:44:23PM -0400, Konrad Rzeszutek Wilk wrote:
> > The problem is to identify, when the pmap module gets a request to
> > map a an address, if this is a PA (which has to be translated to a MA), or
> > if it's already a MA.
> > Device drivers requests are already identified as being MA (thanks to the
> > bus_space interface, driver requests have their own path separate from
> > VM requests). The problem is when a mapping request comes from userland
> > via /dev/mem: we don't know if it is a PA or a MA (it depends on who is
> > doing the request) and as both spaces uses the same addresses there
> > are conflicts.
> 
> Right, but the address that is provided I presume is a physical address?

physical or machine, depending on what the userland process wants.

> And based on that, and on the E820 (where that data is plugged in the
> P2M array/tree), you can figure out whether to treat this as MA or PA?

I can't see how, as the 2 spaces have overlapping addresses.
For a domain with 512MB RAM, Xen gives a physical address space of
0x0 -> 0x20000000. The ISA hole (for example) is at machine
address 0x0a0000 -> 0x100000 (there are memory-mapped ressources outside
this range too). When a process mmaps /dev/mem at 0x0a0000, how do
you know if it wants the RAM at physical address 0x0a0000 (this address then
has to be translated to machine address), or a device mapped
at machine address 0x0a0000 ?

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