On 10/04/2012 11:39 PM, Jan Beulich wrote:
We should have the check, but at least for Linux support we require
P <= V-2.
Not really imo - P <= V - 1 should be sufficient here, as all that is
necessary is that the result represents a 1:1 mapping. Specifically,
there's no constraint to the virtual space limitation of the direct
mapping of RAM.
The P <= V-2 limitation doesn't come from this, it comes from the fact
that we need to have the regular kernel 1:1 map and still have space for
the kernel, vmalloc, ioremap and so on in the kernel part of the address
space; in theory it *could* be some fraction between 1 and 2, but since
hardware doesn't do fractional bits very well the above is what we have
been telling the hardware folks. :)
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
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