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>
Reviewed-by: Laszlo Ersek <lersek@redhat.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 fedbaee07ec7..40a22f66dc22 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
--
2.9.5
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