Re: [virtio-dev] [PATCH v3] content: support SR-IOV

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, May 22, 2018 at 06:26:15PM +0800, Tiwei Bie wrote:
> Allocate a feature bit for virtio devices which support SR-IOV.
> 
> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
> Fixes: https://github.com/oasis-tcs/virtio-spec/issues/11
> ---
> More details can be found from this thread:
> https://patchwork.kernel.org/patch/10285541/
> 
> This patch needs below patch applied first:
> https://github.com/oasis-tcs/virtio-spec/issues/10
> https://lists.oasis-open.org/archives/virtio-dev/201805/msg00046.html
> 
> v2 -> v3:
> - Improve the wording (Cornelia);
> 
> v1 -> v2:
> - s/Reserve/Allocate/ (MST);
> - Add a Fixes tag (MST);
> - Be more explicit in driver requirement (MST);
> - Remove the "device MAY fail" description (MST);
> - Rebase on IO_BARRIER patch;
> 
> RFC -> v1:
> - Mention PCI in the description (Cornelia);
> 
>  content.tex | 15 +++++++++++++--
>  1 file changed, 13 insertions(+), 2 deletions(-)
> 
> diff --git a/content.tex b/content.tex
> index 95c243f..e9e6f9a 100644
> --- a/content.tex
> +++ b/content.tex
> @@ -95,10 +95,10 @@ Feature bits are allocated as follows:
>  \begin{description}
>  \item[0 to 23] Feature bits for the specific device type
>  
> -\item[24 to 36] Feature bits reserved for extensions to the queue and
> +\item[24 to 37] Feature bits reserved for extensions to the queue and
>    feature negotiation mechanisms
>  
> -\item[37 and above] Feature bits reserved for future extensions.
> +\item[38 and above] Feature bits reserved for future extensions.
>  \end{description}
>  
>  \begin{note}
> @@ -5357,6 +5357,9 @@ Descriptors} and \ref{sec:Packed Virtqueues / Indirect Flag: Scatter-Gather Supp
>    better performance.  This feature indicates whether
>    a stronger form of barrier suitable for hardware
>    devices is necessary.
> +  \item[VIRTIO_F_SR_IOV(37)] This feature indicates that
> +  the device supports Single Root I/O Virtualization.
> +  Currently only PCI devices support this feature.

I guess the assumption is that all VFs and the PF are of the same type?

I feel it might be handy down the road to support mixing
types. For this reason, to avoid binding a wrong driver
to a VF, I propose that all VFs have this bit too,
and require that drivers ignore VFs without this bit.

What do you think?

>  \end{description}
>  
>  \drivernormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
> @@ -5376,6 +5379,11 @@ A driver SHOULD accept VIRTIO_F_IO_BARRIER if it is offered.
>  If VIRTIO_F_IO_BARRIER has been negotiated, a driver MUST use
>  the barriers suitable for hardware devices.
>  
> +A driver SHOULD accept VIRTIO_F_SR_IOV if it is offered.
> +If VIRTIO_F_SR_IOV has been negotiated, a driver can
> +enable virtual functions through the device's PCI SR-IOV
> +capability structure.

I feel the last sentence isn't clear enough.  How about

a driver MUST negotiate VIRTIO_F_SR_IOV and complete the feature
negotiation (including setting the DRIVER_OK \field{status} bit) before
enabling virtual functions through the device's PCI SR-IOV capability
structure.

> +
>  \devicenormative{\section}{Reserved Feature Bits}{Reserved Feature Bits}
>  
>  A device MUST offer VIRTIO_F_VERSION_1.  A device MAY fail to operate further
> @@ -5392,6 +5400,9 @@ buffers in the same order in which they have been available.
>  A device MAY fail to operate further if VIRTIO_F_IO_BARRIER
>  is not accepted.
>  
> +A device SHOULD offer VIRTIO_F_SR_IOV if it presents a PCI
> +SR-IOV capability structure.
> +
>  \section{Legacy Interface: Reserved Feature Bits}\label{sec:Reserved Feature Bits / Legacy Interface: Reserved Feature Bits}
>  
>  Transitional devices MAY offer the following:



> -- 
> 2.17.0
> 
> 
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