linux-kernel - Re: [PATCH v3 03/14] KVM: s390: pv: leak the ASCE page when destroy fails

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Message-ID: <f2902086-6c77-eb7d-c4c9-15abb738b214@redhat.com>
Date:   Fri, 6 Aug 2021 13:39:07 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc:     kvm@...r.kernel.org, cohuck@...hat.com, borntraeger@...ibm.com,
        frankja@...ux.ibm.com, thuth@...hat.com, pasic@...ux.ibm.com,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ulrich.Weigand@...ibm.com
Subject: Re: [PATCH v3 03/14] KVM: s390: pv: leak the ASCE page when destroy
 fails

On 06.08.21 11:32, Claudio Imbrenda wrote:
> On Fri, 6 Aug 2021 09:31:54 +0200
> David Hildenbrand <david@...hat.com> wrote:
> 
>> On 04.08.21 17:40, Claudio Imbrenda wrote:
>>> When a protected VM is created, the topmost level of page tables of
>>> its ASCE is marked by the Ultravisor; any attempt to use that
>>> memory for protected virtualization will result in failure.
>>>
>>> Only a successful Destroy Configuration UVC will remove the marking.
>>>
>>> When the Destroy Configuration UVC fails, the topmost level of page
>>> tables of the VM does not get its marking cleared; to avoid issues
>>> it must not be used again.
>>>
>>> Since the page becomes in practice unusable, we set it aside and
>>> leak it.
>>
>> Instead of leaking, can't we add it to some list and try again later?
>> Or do we only expect permanent errors?
> 
> once the secure VM has been destroyed unsuccessfully, there is nothing
> that can be done, this is a permanent error
> 
>> Also, we really should bail out loud (pr_warn) to tell the admin that
>> something really nasty is going on.
> 
> when a destroy secure VM UVC fails, there are already other warnings
> printed, no need to add one more
> 

Okay, makes sense then to me, thanks! Might be worth adding some of that 
info to the patch description.

-- 
Thanks,

David / dhildenb