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Subject: Re: [PATCH v3 03/14] KVM: s390: pv: leak the ASCE page when destroy
 fails
To:     Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc:     kvm@vger.kernel.org, cohuck@redhat.com, borntraeger@de.ibm.com,
        frankja@linux.ibm.com, thuth@redhat.com, pasic@linux.ibm.com,
        linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
        Ulrich.Weigand@de.ibm.com
References: <20210804154046.88552-1-imbrenda@linux.ibm.com>
 <20210804154046.88552-4-imbrenda@linux.ibm.com>
 <6b75cc71-b996-cf3d-ce57-dbcd475ebc3a@redhat.com>
 <20210806113244.4d0712d2@p-imbrenda>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <f2902086-6c77-eb7d-c4c9-15abb738b214@redhat.com>
Date:   Fri, 6 Aug 2021 13:39:07 +0200
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On 06.08.21 11:32, Claudio Imbrenda wrote:
> On Fri, 6 Aug 2021 09:31:54 +0200
> David Hildenbrand <david@redhat.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