From 76ad23ca82292a8fa3e9f3f8d5637f7aecbb9d69 Mon Sep 17 00:00:00 2001 From: Brijesh Singh Date: Thu, 14 Sep 2017 16:22:44 -0500 Subject: OvmfPkg/VirtioNetDxe: update TechNotes 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 Cc: Jordan Justen Cc: Tom Lendacky Cc: Laszlo Ersek Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Brijesh Singh Reviewed-by: Laszlo Ersek Regression-tested-by: Laszlo Ersek Tested-by: Laszlo Ersek --- OvmfPkg/VirtioNetDxe/TechNotes.txt | 20 +++++++++++++------- 1 file changed, 13 insertions(+), 7 deletions(-) (limited to 'OvmfPkg/VirtioNetDxe') diff --git a/OvmfPkg/VirtioNetDxe/TechNotes.txt b/OvmfPkg/VirtioNetDxe/TechNotes.txt index fedbaee..40a22f6 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 -- cgit v1.1