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

Jason Wang
2023-09-21T04:23:10Z

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?

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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