linux-kernel - Re: [PATCH v4] virtio: add VIRTIO_F_NOTIFICATION

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Message-ID: <87mt44hh5f.fsf@redhat.com>
Date:   Wed, 22 Mar 2023 17:42:20 +0100
From:   Cornelia Huck <cohuck@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Viktor Prutyanov <viktor@...nix.com>
Cc:     jasowang@...hat.com, pasic@...ux.ibm.com, farman@...ux.ibm.com,
        linux-s390@...r.kernel.org, kvm@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, yan@...nix.com
Subject: Re: [PATCH v4] virtio: add VIRTIO_F_NOTIFICATION_DATA feature support

On Wed, Mar 22 2023, "Michael S. Tsirkin" <mst@...hat.com> wrote:

> On Wed, Mar 22, 2023 at 05:10:31PM +0300, Viktor Prutyanov wrote:
>> According to VirtIO spec v1.2, VIRTIO_F_NOTIFICATION_DATA feature
>> indicates that the driver passes extra data along with the queue
>> notifications.
>> 
>> In a split queue case, the extra data is 16-bit available index. In a
>> packed queue case, the extra data is 1-bit wrap counter and 15-bit
>> available index.
>> 
>> Add support for this feature for MMIO, channel I/O and modern PCI
>> transports.
>> 
>> Signed-off-by: Viktor Prutyanov <viktor@...nix.com>
>> ---
>>  v4: remove VP_NOTIFY macro and legacy PCI support, add
>>     virtio_ccw_kvm_notify_with_data to virtio_ccw
>>  v3: support feature in virtio_ccw, remove VM_NOTIFY, use avail_idx_shadow,
>>     remove byte swap, rename to vring_notification_data
>>  v2: reject the feature in virtio_ccw, replace __le32 with u32
>> 
>>  Tested with disabled VIRTIO_F_NOTIFICATION_DATA on qemu-system-s390x
>>  (virtio-blk-ccw), qemu-system-riscv64 (virtio-blk-device,
>>  virtio-rng-device), qemu-system-x86_64 (virtio-blk-pci, virtio-net-pci)
>>  to make sure nothing is broken.
>>  Tested with enabled VIRTIO_F_NOTIFICATION_DATA on 64-bit RISC-V Linux
>>  and my hardware implementation of virtio-rng.
>
> what did you test? virtio pci? mmio? guessing not ccw...
>
> Cornelia could you hack up something to quickly test ccw?

Hm, I'm not entirely sure how notification data is supposed to be used
in real life -- Viktor, what is your virtio-rng implementation doing;
can this be hacked into all transports?

(Also, if the other ccw folks have something handy, please speak up :)