Re: [Xen-devel] [PATCH for 4.13] x86/shim: don't reserve 640k - 1M region in E820

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.10.2019 12:08, Sergey Dyasli wrote:
> On 28/10/2019 09:06, Jan Beulich wrote:
>> On 28.10.2019 09:56, Sergey Dyasli wrote:
>>> Converting a guest from PV to PV-in-PVH makes the guest to have 384k
>>> less memory, which may confuse guest's balloon driver. This happens
>>> because Xen unconditionally reserves 640k - 1M region in E820 despite
>>> the fact that it's really a usable RAM in PVH boot mode.
>>
>> This is a PVH property according to your description and according
>> to my understanding. Why would you then ...
>>
>>> Fix this by skipping the region type change for pv-shim mode.
>>
>> ... alter behavior for shim mode only, rather than when booted in
>> PVH mode in general?
> 
> This is just me being cautious.
> 
> My original email does have this text after ---
> "The condition can be relaxed to be just !pvh_boot if there are no
> plans to support VGA MMIO / ROMs for PVH guests."

I doubt emulated ones are intended to be supported, but of
course a graphics card could be passed through. Iirc passthrough
is a pending work item still anyway for PVH, so dealing with the
case right now may not even be necessary.

Jan

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