Re: [Xen-devel] mapping of memory below 16Mb

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 24/1/08 15:15, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> One point I got a little surprised about while doing the 1Gb page support:
> The 1:1 mapping of the low 16 Mb (and most significantly the first Mb)
> created at boot time is being retained permanently. Shouldn't Xen be
> following the E820 map also for this memory range (by either not
> mapping non-RAM at all or at best mapping them UC/WP)?

Below 1MB is a special case, and 1MB-16MB we're dodging BIOS tables, not
actual hardware. At least this is the case for all system I know about. If
there are exceptions which we care about, then we can try harder. Otherwise
that code is quite complicated enough as it is.

> The WP attribute raises another question: Are there any plans to make
> Xen use PAT rather than (relying on) MTRRs? Linux folks seem to be
> finally getting closer to this, too, so even virtual PAT support may be
> needed in not too distant future...

We already support PAT for both PV guests and HVM guests.

 -- Keir

> Jan
> 
> 
> 
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