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[2003:cb:c701:d200:ee5d:1275:f171:136d]) by smtp.gmail.com with ESMTPSA id o11-20020a5d408b000000b0020c9520a940sm4946313wrp.54.2022.05.12.06.22.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 May 2022 06:22:18 -0700 (PDT) Message-ID: <77f6f5e7-5945-c478-0e41-affed62252eb@redhat.com> Date: Thu, 12 May 2022 15:22:17 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.0 Content-Language: en-US To: Janis Schoetterl-Glausch , Paolo Bonzini , Jonathan Corbet , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , Heiko Carstens , Vasily Gorbik , Alexander Gordeev Cc: Sven Schnelle , kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org References: <20220512131019.2594948-1-scgl@linux.ibm.com> <20220512131019.2594948-2-scgl@linux.ibm.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH v3 1/2] KVM: s390: Don't indicate suppression on dirtying, failing memop In-Reply-To: <20220512131019.2594948-2-scgl@linux.ibm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On 12.05.22 15:10, Janis Schoetterl-Glausch wrote: > If user space uses a memop to emulate an instruction and that > memop fails, the execution of the instruction ends. > Instruction execution can end in different ways, one of which is > suppression, which requires that the instruction execute like a no-op. > A writing memop that spans multiple pages and fails due to key > protection may have modified guest memory, as a result, the likely > correct ending is termination. Therefore, do not indicate a > suppressing instruction ending in this case. I think that is possibly problematic handling. In TCG we stumbled in similar issues in the past for MVC when crossing page boundaries. Failing after modifying the first page already seriously broke some user space, because the guest would retry the instruction after fixing up the fault reason on the second page: if source and destination operands overlap, you'll be in trouble because the input parameters already changed. For this reason, in TCG we make sure that all accesses are valid before starting modifications. See target/s390x/tcg/mem_helper.c:do_helper_mvc with access_prepare() and friends as an example. Now, I don't know how to tackle that for KVM, I just wanted to raise awareness that injecting an interrupt after modifying page content is possible dodgy and dangerous. -- Thanks, David / dhildenb