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[91.12.97.4]) by smtp.gmail.com with ESMTPSA id b15sm9184520wrx.73.2021.08.06.04.39.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Aug 2021 04:39:08 -0700 (PDT) Subject: Re: [PATCH v3 03/14] KVM: s390: pv: leak the ASCE page when destroy fails To: Claudio Imbrenda 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 Organization: Red Hat Message-ID: Date: Fri, 6 Aug 2021 13:39:07 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210806113244.4d0712d2@p-imbrenda> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06.08.21 11:32, Claudio Imbrenda wrote: > On Fri, 6 Aug 2021 09:31:54 +0200 > David Hildenbrand 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