On 09/11/17 14:16, Brijesh Singh wrote:
> In next patches we will update Virtio transmit to use the device-mapped
> address of the caller-supplied packet. The patch documents the new model.
>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> OvmfPkg/VirtioNetDxe/TechNotes.txt | 20 +++++++++++++-------
> 1 file changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/OvmfPkg/VirtioNetDxe/TechNotes.txt b/OvmfPkg/VirtioNetDxe/TechNotes.txt
> index f39426fb13e4..c6ca341ead15 100644
> --- a/OvmfPkg/VirtioNetDxe/TechNotes.txt
> +++ b/OvmfPkg/VirtioNetDxe/TechNotes.txt
> @@ -312,10 +312,14 @@ in the following:
> that is shared by all of the head descriptors. This virtio-net request header
> is never modified by the host.
>
> -- Each tail descriptor is re-pointed to the caller-supplied packet buffer
> - whenever VirtioNetTransmit places the corresponding head descriptor on the
> - Available Ring. The caller is responsible to hang on to the unmodified buffer
> - until it is reported transmitted by VirtioNetGetStatus.
> +- Each tail descriptor is re-pointed to the device-mapped address of the
> + caller-supplied packet buffer whenever VirtioNetTransmit places the
> + corresponding head descriptor on the Available Ring. A reverse mapping, from
> + the device-mapped address to the caller-supplied packet address, is saved in
> + an associative data structure that belongs to the driver instance.
> +
> +- Per spec, the caller is responsible to hang on to the unmodified packet
> + buffer until it is reported transmitted by VirtioNetGetStatus.
>
> Steps of packet transmission:
>
> @@ -338,9 +342,11 @@ Steps of packet transmission:
> - Client code calls VirtioNetGetStatus. In case the Used Ring is empty, the
> function reports no Tx completion. Otherwise, a head descriptor's index is
> consumed from the Used Ring and recycled to the private stack. The client
> - code's original packet buffer address is fetched from the tail descriptor
> - (where it has been stored at VirtioNetTransmit time) and returned to the
> - caller.
> + code's original packet buffer address is calculated by fetching the
> + device-mapped address from the tail descriptor (where it has been stored at
> + VirtioNetTransmit time), and by looking up the device-mapped address in the
> + associative data structure. The reverse-mapped packet buffer address is
> + returned to the caller.
>
> - The Len field of the Used Ring Element is not checked. The host is assumed to
> have transmitted the entire packet -- VirtioNetTransmit had forced it below
>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
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