Re: [virtio-comment] [PATCH v3] virtio-vsock: add max payload size config field

[Stefano Garzarella <sgarzare@redhat.com>]

On Thu, Apr 21, 2022 at 01:29:39PM +0300, Laura Loghin wrote:
>Added a new field to the vsock device config space that
>is limiting the size of the packet payload. This way
>the driver is not allowed to allocate huge buffers, and
>potentially fill up the entire memory.
>Also defined a new feature bit for this, VIRTIO_VSOCK_F_SIZE_MAX,
>in order to keep backwards compatibility.
>
>Signed-off-by: Laura Loghin <lauralg@amazon.com>
>---
> virtio-vsock.tex | 24 ++++++++++++++++++++++++
> 1 file changed, 24 insertions(+)

Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>

>
>diff --git a/virtio-vsock.tex b/virtio-vsock.tex
>index d79984d..5db6110 100644
>--- a/virtio-vsock.tex
>+++ b/virtio-vsock.tex
>@@ -23,6 +23,10 @@ \subsection{Feature bits}\label{sec:Device Types / Socket Device / Feature bits}
> \begin{description}
> \item[VIRTIO_VSOCK_F_STREAM (0)] stream socket type is supported.
> \item[VIRTIO_VSOCK_F_SEQPACKET (1)] seqpacket socket type is supported.
>+\item[VIRTIO_VSOCK_F_SIZE_MAX (2)] Maximum size of the packet payload is in
>+	\field{data_max_size}. If offered by the device, device advises driver
>+	about the value of its maximum payload size. If negotiated, the driver uses
>+	\field{data_max_size} as the maximum packet payload size value.
> \end{description}
>
> \subsection{Device configuration layout}\label{sec:Device Types / Socket Device / Device configuration layout}
>@@ -32,6 +36,7 @@ \subsection{Device configuration layout}\label{sec:Device Types / Socket Device
> \begin{lstlisting}
> struct virtio_vsock_config {
> 	le64 guest_cid;
>+	le32 data_max_size;
> };
> \end{lstlisting}
>
>@@ -57,6 +62,25 @@ \subsection{Device configuration layout}\label{sec:Device Types / Socket Device
> \hline
> \end{tabular}
>
>+The following driver-read-only field, \field{data_max_size} only exists if
>+VIRTIO_VSOCK_F_SIZE_MAX is set. This field specifies the maximum packet payload
>+size for the driver to use.
>+
>+\devicenormative{\subsubsection}{Device configuration layout}{Device Types / Socket Device / Device configuration layout}
>+
>+The device MUST NOT change the value exposed through \field{data_max_size}.
>+
>+\drivernormative{\subsubsection}{Device configuration layout}{Device Types / Socket Device / Device configuration layout}
>+
>+A driver SHOULD negotiate VIRTIO_VSOCK_F_SIZE_MAX if the device offers it.
>+
>+If the driver negotiates VIRTIO_VSOCK_F_SIZE_MAX, the receive buffers it
>+supplies for a packet MUST have a total size that doesn't exceed the size
>+\field{data_max_size} (plus header length).
>+
>+If the driver negotiates VIRTIO_VSOCK_F_SIZE_MAX, it MUST  NOT transmit packets
>+of size exceeding the value of \field{data_max_size} (plus header length).
>+
> \subsection{Device Initialization}\label{sec:Device Types / Socket Device / Device Initialization}
>
> \begin{enumerate}
>-- 
>2.17.1
>
>
>
>
>Amazon Development Center (Romania) S.R.L. registered office: 27A Sf. Lazar Street, UBC5, floor 2, Iasi, Iasi County, 700045, Romania. Registered in Romania. Registration number J22/2621/2005.
>
>
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