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(p200300cbc71a5900d1064706528a7cd5.dip0.t-ipconnect.de. [2003:cb:c71a:5900:d106:4706:528a:7cd5]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39d893773b6sm5555224f8f.27.2025.04.10.11.44.05 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 10 Apr 2025 11:44:06 -0700 (PDT) Message-ID: <065d46ba-83c1-473a-9cbe-d5388237d1ea@redhat.com> Date: Thu, 10 Apr 2025 20:44:04 +0200 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] s390/virtio_ccw: don't allocate/assign airqs for non-existing queues To: linux-kernel@vger.kernel.org Cc: linux-s390@vger.kernel.org, virtualization@lists.linux.dev, kvm@vger.kernel.org, Chandra Merla , Stable@vger.kernel.org, Cornelia Huck , Thomas Huth , Halil Pasic , Eric Farman , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , "Michael S. Tsirkin" , Wei Wang References: <20250402203621.940090-1-david@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <20250402203621.940090-1-david@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 02.04.25 22:36, David Hildenbrand wrote: > If we finds a vq without a name in our input array in > virtio_ccw_find_vqs(), we treat it as "non-existing" and set the vq pointer > to NULL; we will not call virtio_ccw_setup_vq() to allocate/setup a vq. > > Consequently, we create only a queue if it actually exists (name != NULL) > and assign an incremental queue index to each such existing queue. > > However, in virtio_ccw_register_adapter_ind()->get_airq_indicator() we > will not ignore these "non-existing queues", but instead assign an airq > indicator to them. > > Besides never releasing them in virtio_ccw_drop_indicators() (because > there is no virtqueue), the bigger issue seems to be that there will be a > disagreement between the device and the Linux guest about the airq > indicator to be used for notifying a queue, because the indicator bit > for adapter I/O interrupt is derived from the queue index. > > The virtio spec states under "Setting Up Two-Stage Queue Indicators": > > ... indicator contains the guest address of an area wherein the > indicators for the devices are contained, starting at bit_nr, one > bit per virtqueue of the device. > > And further in "Notification via Adapter I/O Interrupts": > > For notifying the driver of virtqueue buffers, the device sets the > bit in the guest-provided indicator area at the corresponding > offset. > > For example, QEMU uses in virtio_ccw_notify() the queue index (passed as > "vector") to select the relevant indicator bit. If a queue does not exist, > it does not have a corresponding indicator bit assigned, because it > effectively doesn't have a queue index. > > Using a virtio-balloon-ccw device under QEMU with free-page-hinting > disabled ("free-page-hint=off") but free-page-reporting enabled > ("free-page-reporting=on") will result in free page reporting > not working as expected: in the virtio_balloon driver, we'll be stuck > forever in virtballoon_free_page_report()->wait_event(), because the > waitqueue will not be woken up as the notification from the device is > lost: it would use the wrong indicator bit. > > Free page reporting stops working and we get splats (when configured to > detect hung wqs) like: > > INFO: task kworker/1:3:463 blocked for more than 61 seconds. > Not tainted 6.14.0 #4 > "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. > task:kworker/1:3 [...] > Workqueue: events page_reporting_process > Call Trace: > [<000002f404e6dfb2>] __schedule+0x402/0x1640 > [<000002f404e6f22e>] schedule+0x3e/0xe0 > [<000002f3846a88fa>] virtballoon_free_page_report+0xaa/0x110 [virtio_balloon] > [<000002f40435c8a4>] page_reporting_process+0x2e4/0x740 > [<000002f403fd3ee2>] process_one_work+0x1c2/0x400 > [<000002f403fd4b96>] worker_thread+0x296/0x420 > [<000002f403fe10b4>] kthread+0x124/0x290 > [<000002f403f4e0dc>] __ret_from_fork+0x3c/0x60 > [<000002f404e77272>] ret_from_fork+0xa/0x38 > > There was recently a discussion [1] whether the "holes" should be > treated differently again, effectively assigning also non-existing > queues a queue index: that should also fix the issue, but requires other > workarounds to not break existing setups. > > Let's fix it without affecting existing setups for now by properly ignoring > the non-existing queues, so the indicator bits will match the queue > indexes. > > [1] https://lore.kernel.org/all/cover.1720611677.git.mst@redhat.com/ > > Fixes: a229989d975e ("virtio: don't allocate vqs when names[i] = NULL") > Reported-by: Chandra Merla > Cc: > Cc: Cornelia Huck > Cc: Thomas Huth > Cc: Halil Pasic > Cc: Eric Farman > Cc: Heiko Carstens > Cc: Vasily Gorbik > Cc: Alexander Gordeev > Cc: Christian Borntraeger > Cc: Sven Schnelle > Cc: "Michael S. Tsirkin" > Cc: Wei Wang > Signed-off-by: David Hildenbrand > --- So, given that (a) people are actively running into this (b) we'll have to backport this quite a lot (c) the spec issue is not a s390x-only issue (d) it's still unclear how to best deal with the spec issue I suggest getting this fix here upstream asap. It will neither making sorting out the spec issue easier nor harder :) I can spot it in the s390 fixes tree already. -- Cheers, David / dhildenb