Re: [virtio-dev] Re: [VIRTIO PCI PATCH v5 1/1] transport-pci: Add freeze_mode to virtio_pci_common_cfg

[Jason Wang]

On Thu, Sep 21, 2023 at 2:28 PM Chen, Jiqian <Jiqian.Chen@xxxxxxx> wrote:
>
> Hi Jason,
>
> On 2023/9/21 12:22, Jason Wang wrote:
> > On Tue, Sep 19, 2023 at 7:43 PM Jiqian Chen <Jiqian.Chen@xxxxxxx> 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 beginning, I just wanted to add a new feature flag VIRTIO_GPU_F_FREEZE_S3 for virtio-gpu since I encountered virtio-gpu issue during guest S3, so that the guest and qemu can negotiate and change the reset behavior during S3. But Parav 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 expanding its influence is appropriate, I have not received any feedback from others, so I change it to the pci level and made this version.
> If you are interested, please see the previous version: https://lists.oasis-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@xxxxxxx>
> >> ---
> >>  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 layout}\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 layout}\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 buffer
> >> --
> >> 2.34.1
> >>
> >
> >
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>
> --
> Best regards,
> Jiqian Chen.