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From:   Jason Wang <jasowang@redhat.com>
Date:   Fri, 22 Sep 2023 11:17:35 +0800
Message-ID: <CACGkMEtx-i_9dgdONFzEmmWYNRhaoJQZX7a5OmLfDvGoUaajPQ@mail.gmail.com>
Subject: Re: [virtio-dev] Re: [VIRTIO PCI PATCH v5 1/1] transport-pci: Add
 freeze_mode to virtio_pci_common_cfg
To:     "Chen, Jiqian" <Jiqian.Chen@amd.com>
Cc:     Gerd Hoffmann <kraxel@redhat.com>,
        "Michael S . Tsirkin" <mst@redhat.com>,
        Xuan Zhuo <xuanzhuo@linux.alibaba.com>,
        David Airlie <airlied@redhat.com>,
        Gurchetan Singh <gurchetansingh@chromium.org>,
        Chia-I Wu <olvaffe@gmail.com>,
        =?UTF-8?B?TWFyYy1BbmRyw6kgTHVyZWF1?= <marcandre.lureau@gmail.com>,
        Robert Beckett <bob.beckett@collabora.com>,
        Mikhail Golubev-Ciuchea <Mikhail.Golubev-Ciuchea@opensynergy.com>,
        Parav Pandit <parav@nvidia.com>,
        "virtio-comment@lists.oasis-open.org" 
        <virtio-comment@lists.oasis-open.org>,
        "virtio-dev@lists.oasis-open.org" <virtio-dev@lists.oasis-open.org>,
        "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Stefano Stabellini <sstabellini@kernel.org>,
        =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= <roger.pau@citrix.com>,
        "Deucher, Alexander" <Alexander.Deucher@amd.com>,
        "Koenig, Christian" <Christian.Koenig@amd.com>,
        "Hildebrand, Stewart" <Stewart.Hildebrand@amd.com>,
        Xenia Ragiadakou <burzalodowa@gmail.com>,
        "Huang, Honglei1" <Honglei1.Huang@amd.com>,
        "Zhang, Julia" <Julia.Zhang@amd.com>,
        "Huang, Ray" <Ray.Huang@amd.com>
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On Thu, Sep 21, 2023 at 2:28=E2=80=AFPM Chen, Jiqian <Jiqian.Chen@amd.com> =
wrote:
>
> Hi Jason,
>
> On 2023/9/21 12:22, Jason Wang wrote:
> > On Tue, Sep 19, 2023 at 7:43=E2=80=AFPM Jiqian Chen <Jiqian.Chen@amd.co=
m> wrote:
> >>
> >> When guest vm does S3, Qemu will reset and clear some things of virtio
> >> devices, but guest can't aware that, so that may cause some problems.
> >> For excample, Qemu calls virtio_reset->virtio_gpu_gl_reset when guest
> >> resume, that function will destroy render resources of virtio-gpu. As
> >> a result, after guest resume, the display can't come back and we only
> >> saw a black screen. Due to guest can't re-create all the resources, so
> >> we need to let Qemu not to destroy them when S3.
> >>
> >> For above purpose, we need a mechanism that allows guests and QEMU to
> >> negotiate their reset behavior. So this patch add a new parameter
> >> named freeze_mode to struct virtio_pci_common_cfg. And when guest
> >> suspends, it can write freeze_mode to be FREEZE_S3, and then virtio
> >> devices can change their reset behavior on Qemu side according to
> >> freeze_mode. What's more, freeze_mode can be used for all virtio
> >> devices to affect the behavior of Qemu, not just virtio gpu device.
> >
> > A simple question, why is this issue specific to pci?
> I thought you possibly missed the previous version patches. At the beginn=
ing, I just wanted to add a new feature flag VIRTIO_GPU_F_FREEZE_S3 for vir=
tio-gpu since I encountered virtio-gpu issue during guest S3, so that the g=
uest and qemu can negotiate and change the reset behavior during S3. But Pa=
rav and Mikhail hoped me can improve the feature to a pci level, then other=
 virtio devices can also benefit from it. Although I am not sure if expandi=
ng its influence is appropriate, I have not received any feedback from othe=
rs, so I change it to the pci level and made this version.
> If you are interested, please see the previous version: https://lists.oas=
is-open.org/archives/virtio-comment/202307/msg00209.html, thank you.

This is not a good answer. Let me ask you differently, why don't you
see it in other forms of transport like virtio-gpu-mmio?

Thanks

>
> >
> > Thanks
> >
> >
> >>
> >> Signed-off-by: Jiqian Chen <Jiqian.Chen@amd.com>
> >> ---
> >>  transport-pci.tex | 7 +++++++
> >>  1 file changed, 7 insertions(+)
> >>
> >> diff --git a/transport-pci.tex b/transport-pci.tex
> >> index a5c6719..2543536 100644
> >> --- a/transport-pci.tex
> >> +++ b/transport-pci.tex
> >> @@ -319,6 +319,7 @@ \subsubsection{Common configuration structure layo=
ut}\label{sec:Virtio Transport
> >>          le64 queue_desc;                /* read-write */
> >>          le64 queue_driver;              /* read-write */
> >>          le64 queue_device;              /* read-write */
> >> +        le16 freeze_mode;               /* read-write */
> >>          le16 queue_notif_config_data;   /* read-only for driver */
> >>          le16 queue_reset;               /* read-write */
> >>
> >> @@ -393,6 +394,12 @@ \subsubsection{Common configuration structure lay=
out}\label{sec:Virtio Transport
> >>  \item[\field{queue_device}]
> >>          The driver writes the physical address of Device Area here.  =
See section \ref{sec:Basic Facilities of a Virtio Device / Virtqueues}.
> >>
> >> +\item[\field{freeze_mode}]
> >> +        The driver writes this to set the freeze mode of virtio pci.
> >> +        VIRTIO_PCI_FREEZE_MODE_UNFREEZE - virtio-pci is running;
> >> +        VIRTIO_PCI_FREEZE_MODE_FREEZE_S3 - guest vm is doing S3, and =
virtio-pci enters S3 suspension;
> >> +        Other values are reserved for future use, like S4, etc.
> >> +
> >>  \item[\field{queue_notif_config_data}]
> >>          This field exists only if VIRTIO_F_NOTIF_CONFIG_DATA has been=
 negotiated.
> >>          The driver will use this value when driver sends available bu=
ffer
> >> --
> >> 2.34.1
> >>
> >
> >
> > ---------------------------------------------------------------------
> > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org
> > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org
> >
>
> --
> Best regards,
> Jiqian Chen.