From: Jason Wang <jasowang@redhat.com>
To: Parav Pandit <parav@nvidia.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
"virtio-dev@lists.oasis-open.org"
<virtio-dev@lists.oasis-open.org>,
"cohuck@redhat.com" <cohuck@redhat.com>,
"virtio-comment@lists.oasis-open.org"
<virtio-comment@lists.oasis-open.org>,
Shahaf Shuler <shahafs@nvidia.com>,
Satananda Burla <sburla@marvell.com>,
Maxime Coquelin <maxime.coquelin@redhat.com>,
Yan Vugenfirer <yan@daynix.com>
Subject: Re: [virtio-comment] Re: [PATCH 09/11] transport-pci: Describe PCI MMR dev config registers
Date: Fri, 14 Apr 2023 11:08:40 +0800 [thread overview]
Message-ID: <CACGkMEskPJgNrBQV10ieSaKCg_kBbi2E0z1BEbdyiiaDdD1zJA@mail.gmail.com> (raw)
In-Reply-To: <f9f01f9d-f6ec-0daa-a11d-c75589dcbe6c@nvidia.com>
On Fri, Apr 14, 2023 at 1:24 AM Parav Pandit <parav@nvidia.com> wrote:
>
>
>
> On 4/13/2023 1:14 AM, Jason Wang wrote:
>
> >> For LM BAR length and number should be same between two PCI VFs. But its
> >> orthogonal to this point. Such checks will be done anyway.
> >
> > Quoted the wrong sections, I think it should be:
> >
> > "
> > length MAY include padding, or fields unused by the driver, or future
> > extensions. Note: For example, a future device might present a large
> > structure size of several MBytes. As current devices never utilize
> > structures larger than 4KBytes in size, driver MAY limit the mapped
> > structure size to e.g. 4KBytes (thus ignoring parts of structure after
> > the first 4KBytes) to allow forward compatibility with such devices
> > without loss of functionality and without wasting resources.
> > "
> yes. This is the one.
>
> > If it's a transitional device but not placed at BAR0, it might have
> > side effects for Linux drivers which assumes BAR0 for legacy.
> >
> True. Transitional can be at BAR0.
>
> > I don't see how easy it could be a non transitional device:
> >
> > "
> > Devices or drivers with no legacy compatibility are referred to as
> > non-transitional devices and drivers, respectively.
> > "
> Michael has suggested rewording of the text.
> It is anyway new text so lets park it aside for now.
> It is mostly tweaking the text.
>
> >
> >> device can expose this optional capability and its attached MMIO region.
> >>
> >> Spec changes are similar to #2.
> >>> - non trivial spec changes which ends up of the tricky cases that
> >>> tries to workaround legacy to fit for a hardware implementation
> >>> - work only for the case of virtualization with the help of
> >>> meditation, can't work for bare metal
> >> For bare-metal PFs usually thin hypervisors are used that does very
> >> minimal setup. But I agree that bare-metal is relatively less important.
> >
> > This is not what I understand. I know several vendors that are using
> > virtio devices for bare metal.
> >
> I was saying the case for legacy bare metal is less of a problem because
> PCIe does not limit functionality, perf is still limited due to IOBAR.
>
> >>
> >>> - only work for some specific archs without SVQ
> >>>
> >> That is the legacy limitation that we don't worry about.
> >>
> >>> 2) allow BAR0 to be MMIO for transitional device
> >>>
> >>> Pros:
> >>> - very minor change for the spec
> >> Spec changes wise they are similar to #1.
> >
> > This is different since the changes for this are trivial.
> >
> >>> - work for virtualization (and it work even without dedicated
> >>> mediation for some setups)
> >> I am not aware where can it work without mediation. Do you know any
> >> specific kernel version where it actually works?
> >
> > E.g current Linux driver did:
> >
> > rc = pci_request_region(pci_dev, 0, "virtio-pci-legacy");
> >
> > It doesn't differ from I/O with memory. It means if you had a
> > "transitional" device with legacy MMIO BAR0, it just works.
> >
>
> Thanks to the abstract PCI API in Linux.
And this (legacy MMIO bar) has been supported by DPDK as well for a while.
>
> >>> - work for bare metal for some setups (without mediation)
> >>> Cons:
> >>> - only work for some specific archs without SVQ
> >>> - BAR0 is required
> >>>
> >> Both are not limitation as they are mainly coming from the legacy side
> >> of things.
> >>
> >>> 3) modern device mediation for legacy
> >>>
> >>> Pros:
> >>> - no changes in the spec
> >>> Cons:
> >>> - require mediation layer in order to work in bare metal
> >>> - require datapath mediation like SVQ to work for virtualization
> >>>
> >> Spec change is still require for net and blk because modern device do
> >> not understand legacy, even with mediation layer.
> >
> > That's fine and easy since we work on top of modern devices.
> >
> >> FEATURE_1, RW cap via CVQ which is not really owned by the hypervisor.
> >
> > Hypervisors can trap if they wish.
> >
> Trapping non legacy accessing for 1.x doesn't make sense.
Actually not, I think I've mentioned the reason for several times:
It's a must for ABI and migration compatibility:
1) The offset is not necessarily a page boundary
2) The length is not necessarily times of a PAGE_SIZE
3) PAGE_SIZE varies among different archs
4) Two vendors may have two different layout for the structure
Thanks
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next prev parent reply other threads:[~2023-04-14 3:08 UTC|newest]
Thread overview: 199+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-30 22:58 [virtio-comment] [PATCH 00/11] Introduce transitional mmr pci device Parav Pandit
2023-03-30 22:58 ` [virtio-comment] [PATCH 01/11] transport-pci: Use lowecase alphabets Parav Pandit
2023-03-30 22:58 ` [virtio-comment] [PATCH 02/11] transport-pci: Move transitional device id to legacy section Parav Pandit
2023-03-31 6:43 ` [virtio-comment] " Michael S. Tsirkin
2023-03-31 21:24 ` [virtio-comment] " Parav Pandit
2023-04-02 7:54 ` [virtio-comment] " Michael S. Tsirkin
2023-04-03 14:42 ` [virtio-comment] " Parav Pandit
2023-04-03 14:50 ` [virtio-comment] " Michael S. Tsirkin
2023-04-03 14:58 ` [virtio-comment] " Parav Pandit
2023-04-03 15:14 ` [virtio-comment] " Michael S. Tsirkin
2023-03-30 22:58 ` [virtio-comment] [PATCH 03/11] transport-pci: Split notes of PCI Device Layout Parav Pandit
2023-03-30 22:58 ` [virtio-comment] [PATCH 04/11] transport-pci: Rename and move legacy PCI Device layout section Parav Pandit
2023-03-30 22:58 ` [virtio-comment] [PATCH 05/11] introduction: Add missing helping verb Parav Pandit
2023-03-30 22:58 ` [virtio-comment] [PATCH 06/11] introduction: Introduce transitional MMR interface Parav Pandit
2023-04-07 9:17 ` [virtio-comment] " Michael S. Tsirkin
2023-03-30 22:58 ` [virtio-comment] [PATCH 07/11] transport-pci: Introduce transitional MMR device id Parav Pandit
2023-04-04 7:28 ` [virtio-comment] " Michael S. Tsirkin
2023-04-04 16:08 ` Parav Pandit
2023-04-07 12:03 ` Michael S. Tsirkin
2023-04-07 15:18 ` Parav Pandit
2023-04-07 15:51 ` Michael S. Tsirkin
2023-04-09 3:15 ` Parav Pandit
2023-04-10 10:18 ` Michael S. Tsirkin
2023-04-10 14:34 ` Parav Pandit
2023-04-10 19:58 ` Michael S. Tsirkin
2023-04-10 20:16 ` Parav Pandit
2023-04-07 8:37 ` Michael S. Tsirkin
2023-03-30 22:58 ` [virtio-comment] [PATCH 08/11] transport-pci: Introduce virtio extended capability Parav Pandit
2023-04-04 7:35 ` [virtio-comment] " Michael S. Tsirkin
2023-04-04 7:54 ` Cornelia Huck
2023-04-04 12:43 ` Michael S. Tsirkin
2023-04-04 13:19 ` Cornelia Huck
2023-04-04 14:37 ` Michael S. Tsirkin
2023-04-10 16:21 ` Parav Pandit
2023-04-10 19:49 ` Michael S. Tsirkin
2023-04-10 19:57 ` [virtio-comment] " Parav Pandit
2023-04-10 20:02 ` [virtio-comment] " Michael S. Tsirkin
2023-04-11 8:39 ` Cornelia Huck
2023-04-04 21:18 ` [virtio-comment] " Parav Pandit
2023-04-05 5:10 ` [virtio-comment] " Michael S. Tsirkin
2023-04-05 13:16 ` [virtio-comment] " Parav Pandit
2023-04-07 8:15 ` [virtio-comment] " Michael S. Tsirkin
2023-04-10 1:36 ` [virtio-comment] Re: [virtio-dev] " Jason Wang
2023-04-10 6:24 ` Michael S. Tsirkin
2023-04-10 7:16 ` Jason Wang
2023-04-10 10:04 ` Michael S. Tsirkin
2023-04-11 2:19 ` Jason Wang
2023-04-11 7:00 ` Michael S. Tsirkin
2023-04-11 9:07 ` Jason Wang
2023-04-11 10:43 ` Michael S. Tsirkin
2023-04-11 13:59 ` [virtio-comment] " Parav Pandit
2023-04-11 14:11 ` [virtio-comment] " Michael S. Tsirkin
2023-04-11 13:47 ` Parav Pandit
2023-04-11 14:02 ` Michael S. Tsirkin
2023-04-11 14:07 ` Parav Pandit
2023-04-11 14:10 ` Michael S. Tsirkin
2023-04-11 14:30 ` Parav Pandit
2023-04-10 17:54 ` Parav Pandit
2023-04-10 17:58 ` Parav Pandit
2023-04-11 3:28 ` Jason Wang
2023-04-11 19:01 ` [virtio-comment] " Parav Pandit
2023-04-11 21:25 ` [virtio-comment] " Michael S. Tsirkin
2023-04-12 0:40 ` [virtio-comment] " Parav Pandit
2023-04-12 2:56 ` [virtio-comment] " Michael S. Tsirkin
2023-04-12 4:07 ` Jason Wang
2023-04-12 4:20 ` Michael S. Tsirkin
2023-04-12 4:53 ` Jason Wang
2023-04-12 5:25 ` Michael S. Tsirkin
2023-04-12 5:37 ` Jason Wang
2023-04-13 17:03 ` Michael S. Tsirkin
2023-04-12 4:04 ` Jason Wang
2023-04-12 4:13 ` [virtio-comment] " Parav Pandit
2023-04-12 4:20 ` [virtio-comment] " Michael S. Tsirkin
2023-04-12 4:55 ` Jason Wang
2023-05-19 6:10 ` [virtio-comment] " Michael S. Tsirkin
2023-05-19 21:02 ` [virtio-comment] " Parav Pandit
2023-05-21 5:57 ` [virtio-comment] " Michael S. Tsirkin
2023-05-21 13:24 ` [virtio-comment] " Parav Pandit
2023-05-21 14:34 ` [virtio-comment] " Michael S. Tsirkin
2023-03-30 22:58 ` [virtio-comment] [PATCH 09/11] transport-pci: Describe PCI MMR dev config registers Parav Pandit
2023-04-07 8:55 ` [virtio-comment] " Michael S. Tsirkin
2023-04-10 1:33 ` Jason Wang
2023-04-10 6:14 ` Michael S. Tsirkin
2023-04-10 6:20 ` Jason Wang
2023-04-10 6:39 ` Michael S. Tsirkin
2023-04-10 7:20 ` Jason Wang
2023-04-10 10:06 ` Michael S. Tsirkin
2023-04-11 2:13 ` Jason Wang
2023-04-11 7:04 ` Michael S. Tsirkin
2023-04-11 9:01 ` Jason Wang
[not found] ` <CALBs2cXURMEzCGnULicXbsBfwnKE5cZOz=M-_hhFCXZ=Lqb9Nw@mail.gmail.com>
2023-04-11 10:39 ` Michael S. Tsirkin
2023-04-11 10:42 ` Michael S. Tsirkin
2023-04-12 3:58 ` Jason Wang
2023-04-12 4:15 ` Michael S. Tsirkin
2023-04-12 4:51 ` Jason Wang
2023-04-12 5:01 ` Parav Pandit
2023-04-12 5:14 ` Jason Wang
2023-04-12 5:30 ` Parav Pandit
2023-04-12 5:38 ` Jason Wang
2023-04-12 5:55 ` Parav Pandit
2023-04-12 6:15 ` Jason Wang
2023-04-12 14:23 ` Parav Pandit
2023-04-13 1:48 ` Jason Wang
2023-04-13 3:31 ` Parav Pandit
2023-04-13 5:14 ` Jason Wang
2023-04-13 17:19 ` Michael S. Tsirkin
2023-04-13 19:39 ` Parav Pandit
2023-04-14 3:09 ` Jason Wang
2023-04-14 3:18 ` Parav Pandit
2023-04-14 3:37 ` Jason Wang
2023-04-14 3:51 ` Parav Pandit
2023-04-14 7:05 ` Michael S. Tsirkin
2023-04-17 3:22 ` Jason Wang
2023-04-17 17:23 ` Parav Pandit
2023-04-17 20:26 ` Michael S. Tsirkin
2023-04-17 20:28 ` Parav Pandit
2023-04-18 0:36 ` Jason Wang
2023-04-18 1:30 ` Parav Pandit
2023-04-18 11:58 ` Michael S. Tsirkin
2023-04-18 12:09 ` Parav Pandit
2023-04-18 12:30 ` Michael S. Tsirkin
2023-04-18 12:36 ` Parav Pandit
2023-04-18 1:01 ` Jason Wang
2023-04-18 1:48 ` Parav Pandit
2023-04-13 17:24 ` Parav Pandit
2023-04-13 21:02 ` Michael S. Tsirkin
2023-04-13 21:08 ` Parav Pandit
2023-04-14 2:36 ` Jason Wang
2023-04-14 2:43 ` Parav Pandit
2023-04-14 6:57 ` Michael S. Tsirkin
2023-04-16 13:41 ` Parav Pandit
2023-04-16 20:44 ` Michael S. Tsirkin
2023-04-17 16:59 ` Parav Pandit
2023-04-18 1:09 ` Jason Wang
2023-04-18 1:37 ` Parav Pandit
2023-04-14 6:58 ` Michael S. Tsirkin
2023-04-14 3:08 ` Jason Wang [this message]
2023-04-14 3:13 ` Parav Pandit
2023-04-14 3:18 ` Jason Wang
2023-04-14 3:22 ` Parav Pandit
2023-04-14 3:29 ` Jason Wang
2023-04-11 13:57 ` Parav Pandit
2023-04-12 4:33 ` Michael S. Tsirkin
2023-03-30 22:58 ` [virtio-comment] [PATCH 10/11] transport-pci: Use driver notification PCI capability Parav Pandit
2023-04-12 4:31 ` [virtio-comment] " Michael S. Tsirkin
2023-04-12 4:37 ` [virtio-comment] " Parav Pandit
2023-04-12 4:43 ` [virtio-comment] " Michael S. Tsirkin
2023-04-12 4:48 ` [virtio-comment] " Parav Pandit
2023-04-12 5:02 ` [virtio-comment] " Michael S. Tsirkin
2023-04-12 5:06 ` Parav Pandit
2023-04-12 5:17 ` Michael S. Tsirkin
2023-04-12 5:24 ` Parav Pandit
2023-04-12 5:27 ` Michael S. Tsirkin
2023-03-30 22:58 ` [virtio-comment] [PATCH 11/11] conformance: Add transitional MMR interface conformance Parav Pandit
2023-03-31 7:03 ` [virtio-comment] Re: [PATCH 00/11] Introduce transitional mmr pci device Michael S. Tsirkin
2023-03-31 21:43 ` Parav Pandit
2023-04-03 14:53 ` Michael S. Tsirkin
2023-04-03 14:57 ` [virtio-comment] " Parav Pandit
2023-04-03 15:06 ` [virtio-comment] " Michael S. Tsirkin
2023-04-03 15:16 ` [virtio-comment] " Parav Pandit
2023-04-03 15:23 ` [virtio-comment] " Michael S. Tsirkin
2023-04-03 15:34 ` Michael S. Tsirkin
2023-04-03 15:47 ` [virtio-comment] " Parav Pandit
2023-04-03 17:28 ` [virtio-comment] " Michael S. Tsirkin
2023-04-03 17:35 ` Parav Pandit
2023-04-03 17:39 ` Michael S. Tsirkin
2023-04-03 15:36 ` Parav Pandit
2023-04-03 17:16 ` Michael S. Tsirkin
2023-04-03 17:29 ` Parav Pandit
2023-04-03 18:02 ` Michael S. Tsirkin
2023-04-03 20:25 ` Parav Pandit
2023-04-03 21:04 ` Michael S. Tsirkin
2023-04-03 22:00 ` Parav Pandit
2023-04-07 9:35 ` Michael S. Tsirkin
2023-04-10 1:52 ` Jason Wang
2023-04-03 14:45 ` [virtio-comment] " Stefan Hajnoczi
2023-04-03 14:53 ` Parav Pandit
2023-04-03 17:48 ` Michael S. Tsirkin
2023-04-03 19:11 ` Stefan Hajnoczi
2023-04-03 20:03 ` Michael S. Tsirkin
2023-04-03 19:48 ` Parav Pandit
2023-04-03 20:02 ` Michael S. Tsirkin
2023-04-03 20:42 ` Parav Pandit
2023-04-03 21:14 ` Michael S. Tsirkin
2023-04-03 22:08 ` Parav Pandit
2023-04-03 19:10 ` Stefan Hajnoczi
2023-04-03 20:27 ` Parav Pandit
2023-04-04 14:30 ` Stefan Hajnoczi
2023-04-12 4:48 ` [virtio-comment] " Michael S. Tsirkin
2023-04-12 4:52 ` [virtio-comment] " Parav Pandit
2023-04-12 5:12 ` [virtio-comment] " Michael S. Tsirkin
2023-04-12 5:15 ` Parav Pandit
2023-04-12 5:23 ` Michael S. Tsirkin
2023-04-12 5:39 ` Parav Pandit
2023-04-12 6:02 ` Parav Pandit
2023-04-12 5:10 ` [virtio-comment] Re: [virtio-dev] " Halil Pasic
2023-04-25 2:42 ` [virtio-comment] " Parav Pandit
2023-05-02 7:17 ` David Edmondson
2023-05-02 13:54 ` Parav Pandit
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