linux-kernel - Re: [PATCH v6 02/20] liveupdate: luo

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Message-ID: <CA+CK2bC6sZe1qYd4=KjqDY-eUb95RBPK-Us+-PZbvkrVsvS5Cw@mail.gmail.com>
Date: Tue, 18 Nov 2025 10:46:35 -0500
From: Pasha Tatashin <pasha.tatashin@...een.com>
To: Jason Gunthorpe <jgg@...dia.com>
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Subject: Re: [PATCH v6 02/20] liveupdate: luo_core: integrate with KHO

> > This won't leak data, as /dev/liveupdate is completely disabled, so
> > nothing preserved in memory will be recoverable.
>
> This seems reasonable, but it is still dangerous.
>
> At the minimum the KHO startup either needs to succeed, panic, or fail
> to online most of the memory (ie run from the safe region only)

Allowing degrade booting using only scratch memory sounds like a very
good compromise. This allows the live-update boot to stay alive as a
sort of "crash kernel," particularly since kdump functionality is not
available here. However, it would require some work in KHO to enable
such a feature.

> The above approach works better for things like VFIO or memfd where
> you can boot significantly safely. Not sure about iommu though, if
> iommu doesn't deserialize properly then it probably corrupts all
> memory too.

Yes, DMA may corrupt memory if KHO is broken, *but* we are discussing
broken LUO recovering, the KHO preserved memory should still stay as
preserved but unretriable, so DMA activity should only happen to those
regions...

Pasha

>
> Jason