Re: [PATCH] hvmloader: probe memory below 4G before allocation for OVMF

[Jan Beulich <jbeulich@xxxxxxxx>]

On 03.04.2020 16:26, Igor Druzhinin wrote:
> On 03/04/2020 14:53, Jan Beulich wrote:
>> On 02.04.2020 18:18, Igor Druzhinin wrote:
>>> The area just below 4G where OVMF image is originally relocated is not
>>> necessarily a hole - it might contain pages preallocated by device model
>>> or the toolstack. By unconditionally populating on top of this memory
>>> the original pages are getting lost while still potentially foreign mapped
>>> in Dom0.
>>
>> When there are pre-allocated pages - have they been orphaned? If
>> so, shouldn't whoever populated them unpopulate rather than
>> orphaning them? Or if not - how is the re-use you do safe?
> 
> There is no signal to the device model when that happens - it has no idea 
> when the
> memory it populated and hold a mapping to becomes suddenly unmapped in the 
> guest.
> Re-use is safe as the memory prepopulated before OVMF starts has not been put
> in use yet until after it's finished initializing.

I guess I'm lacking some details here to fully understand what
you're saying: What is it that may pre-populate this range, and
for what purpose?

Jan