From 0a781bdc7f87f87b8c3ef57c2837f116daa8b580 Mon Sep 17 00:00:00 2001
From: Laszlo Ersek <lersek@redhat.com>
Date: Sat, 12 Mar 2016 14:41:26 +0100
Subject: [PATCH] OvmfPkg: VirtioRngDxe: adapt feature negotiation to
 virtio-1.0

Relative to virtio-0.9.5, virtio-1.0 reverses the order of queue discovery
and feature negotiation. In virtio-1.0, feature negotiation has to
complete first, and the device can also reject a self-inconsistent feature
request through the new VSTAT_FEATURES_OK status bit. (For example if the
driver requests a higher level feature but clears a prerequisite feature.)

Furthermore, we retain the VIRTIO_F_VERSION_1 feature bit if the
VIRTIO_DEVICE_PROTOCOL provider has high enough revision.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
---
 OvmfPkg/VirtioRngDxe/VirtioRng.c | 27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/OvmfPkg/VirtioRngDxe/VirtioRng.c b/OvmfPkg/VirtioRngDxe/VirtioRng.c
index d916534aac..1a186d0408 100644
--- a/OvmfPkg/VirtioRngDxe/VirtioRng.c
+++ b/OvmfPkg/VirtioRngDxe/VirtioRng.c
@@ -242,6 +242,19 @@ VirtioRngInit (
     goto Failed;
   }
 
+  Features &= VIRTIO_F_VERSION_1;
+
+  //
+  // In virtio-1.0, feature negotiation is expected to complete before queue
+  // discovery, and the device can also reject the selected set of features.
+  //
+  if (Dev->VirtIo->Revision >= VIRTIO_SPEC_REVISION (1, 0, 0)) {
+    Status = Virtio10WriteFeatures (Dev->VirtIo, Features, &NextDevStat);
+    if (EFI_ERROR (Status)) {
+      goto Failed;
+    }
+  }
+
   //
   // step 4b -- allocate request virtqueue, just use #0
   //
@@ -290,14 +303,14 @@ VirtioRngInit (
   }
 
   //
-  // step 5 -- Report understood features and guest-tuneables. None are
-  // currently defined for VirtioRng, and no generic features are needed by
-  // this driver.
+  // step 5 -- Report understood features and guest-tuneables.
   //
-  Features &= 0;
-  Status = Dev->VirtIo->SetGuestFeatures (Dev->VirtIo, Features);
-  if (EFI_ERROR (Status)) {
-    goto ReleaseQueue;
+  if (Dev->VirtIo->Revision < VIRTIO_SPEC_REVISION (1, 0, 0)) {
+    Features &= ~(UINT64)VIRTIO_F_VERSION_1;
+    Status = Dev->VirtIo->SetGuestFeatures (Dev->VirtIo, Features);
+    if (EFI_ERROR (Status)) {
+      goto ReleaseQueue;
+    }
   }
 
   //
-- 
2.39.2