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@amd.com> 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@amd.com> 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@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 
> >> 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.