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[91.12.106.22]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-39c30226acfsm11018796f8f.88.2025.04.07.00.18.22 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 07 Apr 2025 00:18:22 -0700 (PDT) Message-ID: <4450ec71-8a8f-478c-a66e-b53d858beb02@redhat.com> Date: Mon, 7 Apr 2025 09:18:21 +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: "Michael S. Tsirkin" Cc: Halil Pasic , linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, virtualization@lists.linux.dev, kvm@vger.kernel.org, Chandra Merla , Stable@vger.kernel.org, Cornelia Huck , Thomas Huth , Eric Farman , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Wei Wang References: <20250402203621.940090-1-david@redhat.com> <20250403161836.7fe9fea5.pasic@linux.ibm.com> <20250404063619.0fa60a41.pasic@linux.ibm.com> <4a33daa3-7415-411e-a491-07635e3cfdc4@redhat.com> <20250404153620.04d2df05.pasic@linux.ibm.com> <20250406144025-mutt-send-email-mst@kernel.org> 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: <20250406144025-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 06.04.25 20:42, Michael S. Tsirkin wrote: > On Fri, Apr 04, 2025 at 03:48:49PM +0200, David Hildenbrand wrote: >> On 04.04.25 15:36, Halil Pasic wrote: >>> On Fri, 4 Apr 2025 12:55:09 +0200 >>> David Hildenbrand wrote: >>> >>>> For virito-balloon, we should probably do the following: >>>> >>>> From 38e340c2bb53c2a7cc7c675f5dfdd44ecf7701d9 Mon Sep 17 00:00:00 2001 >>>> From: David Hildenbrand >>>> Date: Fri, 4 Apr 2025 12:53:16 +0200 >>>> Subject: [PATCH] virtio-balloon: Fix queue index assignment for >>>> non-existing queues >>>> >>>> Signed-off-by: David Hildenbrand >>>> --- >>>> device-types/balloon/description.tex | 22 ++++++++++++++++------ >>>> 1 file changed, 16 insertions(+), 6 deletions(-) >>>> >>>> diff --git a/device-types/balloon/description.tex b/device-types/balloon/description.tex >>>> index a1d9603..a7396ff 100644 >>>> --- a/device-types/balloon/description.tex >>>> +++ b/device-types/balloon/description.tex >>>> @@ -16,6 +16,21 @@ \subsection{Device ID}\label{sec:Device Types / Memory Balloon Device / Device I >>>> 5 >>>> \subsection{Virtqueues}\label{sec:Device Types / Memory Balloon Device / Virtqueues} >>>> + >>>> +\begin{description} >>>> +\item[inflateq] Exists unconditionally. >>>> +\item[deflateq] Exists unconditionally. >>>> +\item[statsq] Only exists if VIRTIO_BALLOON_F_STATS_VQ is set. >>>> +\item[free_page_vq] Only exists if VIRTIO_BALLOON_F_FREE_PAGE_HINT is set. >>>> +\item[reporting_vq] Only exists if VIRTIO_BALLOON_F_PAGE_REPORTING is set. >>> >>> s/is set/is negotiated/? >>> >>> I think we should stick to "feature is offered" and "feature is >>> negotiated". >>> >>>> +\end{description} >>>> + >>>> +\begin{note} >>>> +Virtqueue indexes are assigned sequentially for existing queues, starting >>>> +with index 0; consequently, if a virtqueue does not exist, it does not get >>>> +an index assigned. Assuming all virtqueues exist for a device, the indexes >>>> +are: >>>> + >>>> \begin{description} >>>> \item[0] inflateq >>>> \item[1] deflateq >>>> @@ -23,12 +38,7 @@ \subsection{Virtqueues}\label{sec:Device Types / Memory Balloon Device / Virtque >>>> \item[3] free_page_vq >>>> \item[4] reporting_vq >>>> \end{description} >>>> - >>>> - statsq only exists if VIRTIO_BALLOON_F_STATS_VQ is set. >>>> - >>>> - free_page_vq only exists if VIRTIO_BALLOON_F_FREE_PAGE_HINT is set. >>>> - >>>> - reporting_vq only exists if VIRTIO_BALLOON_F_PAGE_REPORTING is set. >>>> +\end{note} >>>> \subsection{Feature bits}\label{sec:Device Types / Memory Balloon Device / Feature bits} >>>> \begin{description} >>> >>> Sounds good to me! But I'm still a little confused by the "holes". What >>> confuses me is that i can think of at least 2 distinct types of "holes": >>> 1) Holes that can be filled later. The queue conceptually exists, but >>> there is no need to back it with any resources for now because it is >>> dormant (it can be seen a hole in comparison to queues that need to >>> materialize -- vring, notifiers, ...) >>> 2) Holes that can not be filled without resetting the device: i.e. if >>> certain features are not negotiated, then a queue X does not exist, >>> but subsequent queues retain their index. >> >> I think it is not about "negotiated", that might be the wrong terminology. >> >> E.g., in QEMU virtio_balloon_device_realize() we define the virtqueues >> (virtio_add_queue()) if virtio_has_feature(s->host_features). >> >> That is, it's independent of a feature negotiation (IIUC), it's static for >> the device -- "host_features" > > > No no that is a bad idea. Breaks forward compatibility. > > Oh my. I did not realize. It is really broken hopelessly. > > Because, note, the guest looks at the guest features :) Can you elaborate why? statsq = 2 free_page_vq = statsq + host_offered_feat(VIRTIO_BALLOON_F_STATS_VQ) reporting_vq = free_page_vq + host_offered_feat(VIRTIO_BALLOON_F_FREE_PAGE_HINT) Independent of any upcoming features. And if a new feature defines a new virtqueue new_vq = reporting_vq + host_offered_feat(VIRTIO_BALLOON_F_PAGE_REPORTING) We only have to make sure in the spec that these calculations always hold. Querying of the host offered features already happens as part of determining the actual guest usable feature (driver_offered & host_offered). > Now I am beginning to think we should leave the spec alone > and fix the drivers ... Ugh .... We could always say that starting with feature X, queue indexes are fixed again. E.g., VIRTIO_BALLOON_F_X would have it's virtqueue fixed at index 5, independent of the other (older) features where the virtqueue indexes are determined like today. Won't make the implementation easier, though, I'm afraid. (I also thought about a way to query the virtqueue index for a feature, but that's probably overengineering) -- Cheers, David / dhildenb