Re: [Xen-devel] [PATCH] x86/setup: do not relocate below the end of current Xen image placement

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 29.11.17 at 19:56, <daniel.kiper@xxxxxxxxxx> wrote:
> On Tue, Nov 28, 2017 at 07:28:25AM -0700, Jan Beulich wrote:
>> Another option is to consider not moving Xen based on other
>> criteria: The main goal here is to free up memory below 16Mb. If
>> the machine has no memory above 16Mb, moving Xen around
>> won't do any good in this regard.
> 
> This is also an option. However, I am not sure why everything below
> 16 MiB is so precious. I have a feeling that it is related somehow
> to ancient PC days but I do not remember details.

Indeed I believe this was mainly to keep the range free for
ISA-style DMA (like what the 82077 floppy disk controllers do).
There are reportedly other (non-ISA) devices with random
restrictions on the range they can DMA to, however, but I
don't think any goes as low as 16Mb.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel