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Tue, 18 Nov 2025 06:48:22 -0800 (PST) X-Google-Smtp-Source: AGHT+IFrm3GxGBjtmINbt7K1rCocJGlvgD6Ff0LKI7XUHA90nBLUK0Hku97YGJthjHfBMeNVNwT5NQ== X-Received: by 2002:a05:6000:26ce:b0:42b:4279:eddd with SMTP id ffacd0b85a97d-42b5934aca1mr16105266f8f.24.1763477301780; Tue, 18 Nov 2025 06:48:21 -0800 (PST) Received: from [192.168.0.7] ([47.64.114.102]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42b53f174afsm31738370f8f.33.2025.11.18.06.48.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Nov 2025 06:48:21 -0800 (PST) Message-ID: <9d1ee20f-7533-422d-b72e-00d10912997e@redhat.com> Date: Tue, 18 Nov 2025 15:48:20 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] hw/s390x: Fix a possible crash with passed-through virtio devices To: Cornelia Huck , Halil Pasic Cc: qemu-s390x@nongnu.org, Christian Borntraeger , Eric Farman , Matthew Rosato , qemu-devel@nongnu.org, David Hildenbrand , =?UTF-8?Q?C=C3=A9dric_Le_Goater?= References: <20251118093945.35062-1-thuth@redhat.com> <20251118130218.30d3da33.pasic@linux.ibm.com> <50f79156-dd93-40c4-831e-66e558531be8@redhat.com> <87h5urquyq.fsf@redhat.com> From: Thomas Huth Content-Language: en-US Autocrypt: addr=thuth@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=thuth@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 18/11/2025 15.25, Cornelia Huck wrote: > On Tue, Nov 18 2025, Thomas Huth wrote: > >> On 18/11/2025 13.02, Halil Pasic wrote: >>> On Tue, 18 Nov 2025 10:39:45 +0100 >>> Thomas Huth wrote: >>> >>>> Consider the following nested setup: An L1 host uses some virtio device >>>> (e.g. virtio-keyboard) for the L2 guest, and this L2 guest passes this >>>> device through to the L3 guest. Since the L3 guest sees a virtio device, >>>> it might send virtio notifications to the QEMU in L2 for that device. ... >>> So I think it would really make sense to prevent passing through >>> virtio-ccw devices with vfio-ccw. >> >> That could be a nice addition on top (in another patch), but we have to fix >> handle_virtio_ccw_notify() anyway to avoid that the L3 guest can crash QEMU, >> so it's certainly not a replacement for this patch, I think. > > "Prevent crashing" is certainly the correct first step :) > > I'm not sure where we would want prevent assignment of non-dasd > devices. The kernel can't (because we're dealing with a subchannel > driver.) I think maybe management software on top of QEMU? > > The other direction would be supporting things like diag500, so we could > pass through virtio-ccw devices as well. But I'm not really seeing a > use case for it, or is there one? It could be a very nice test setup to check vfio-ccw in CI pipelines (where you likely don't have access to a real DASD) ... but apart from that, I also don't see a real usecase for it. Thomas