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

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Mar 01, 2016 at 03:38:55AM -0700, Jan Beulich wrote:
> >>> 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.

Would it be just better to change that code to scan the E820 instead
of using hard-coded values?

> 
> Jan
> 

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