Subject: Re: [RFC PATCH 00/20] mshv: enable kexec with Hyper-V donated pages and partitions

From: Jork Loeser <[email-masked]>
Date: Mon, 1 Jun 2026 13:15:11 -0700 (PDT)

On Mon, 1 Jun 2026, Pasha Tatashin wrote:

> On 05-31 20:10, Mike Rapoport wrote:

>>>  - A freeze mechanism to lock the tree before serializing for kexec
>>>    (patch 13).
>>
>> There were a lot of effort to make KHO stateless and drop the requirement
>> for finalization/freeze.
>
> Yes, using KHO directly here is incorrect. The state machine is provided
> by LUO, so we should use LUO here. MSHV should provide a file that
> userspace adds to LUO, and all state machine management would be the
> same as for all other clients participating in LU.

The thing is, there is no file handle to rely on. Even once partitions are 
all removed, Hyper-V might hang onto pages (and won't return them even if 
asked). However, these pages very much must be excluded from Linux 
post-kexec, or the system will crash. We cannot rely on UM to ensure 
integrity of memory management.

Contrast that to standard LUO use: If you drop individual file handles, or 
even skip the LUO phase entirely, the worst that will happen is that the 
objects will be gone post-kexec. The MM itself will still be consistent. 
For MSHV & page donation, this is different.

(And yes, partition preservation will very much tie into LUO)

Best,
Jork