Re: [Xen-devel] identify a Xen PV domU to fix devmem_is_allowed

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.02.16 at 16:10, <konrad.wilk@xxxxxxxxxx> wrote:
> On Mon, Feb 29, 2016 at 11:28:49AM +0100, Olaf Hering wrote:
>> What is the correct way to identify a Xen PV domU in the kenrel?
>> devmem_is_allowed() used to disable access to pages < 256 in domU.
>> With pvops this check was removed, or never ported forward.
> 
> CC-ing Boris and Daniel.
> 
> Why is this needed? The first 640KB of memory in a guest are
> RAM pages with no BIOS data in it.

Exactly: devmem_is_allowed() is specifically meant to return true
if and only if the page is not RAM or otherwise special. The
question just is whether what Olaf suggested is also correct for
Dom0 - I don't recall whether the low 1Mb gets 1:1 mapped in
that case.

Jan


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