Re: [Xen-devel] [PATCH v2 0/2] Introduce runstate area registration with phys address

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

Hello Julien,

On 08.05.19 16:39, Julien Grall wrote:
> That's a translation fault level 0 on a stage-1 page-table walk. To confirm you 
> have kpti disabled, right?
Yes, KPTI is disabled. That's why I'm curious what's wrong with that.

> Does it always fail, or only time to time?
It happens on boot. And those prints are permanent and makes boot time 
enormous. I once waited till user prompt (half an hour or so), they calmed on 
visible idle, but printed from time to time (maybe on userspace activities).

> Could you dump the guest register when this happen?
Could you please remember how to do that?

> Even with kpti disabled, you are still potentially facing issue using virtual 
> address (although they may be more difficult to trigger). Indeed, you are 
> relying on the guest OS to unmap the regions or touch the page-tables entries 
> used for the walk.
> Unfortunately we can't prevent a guest playing with its page-table. So at best 
> we can only workaround it.
And that's why we turned to guest phys address used for runstate area.

--
Sincerely,
Andrii Anisov.

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