File vhost-correctly-turn-on-VIRTIO_F_IOMMU_P.patch of Package qemu.20755

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File vhost-correctly-turn-on-VIRTIO_F_IOMMU_P.patch of Package qemu.20755

From: Jason Wang <jasowang@redhat.com>
Date: Mon, 2 Mar 2020 12:24:54 +0800
Subject: vhost: correctly turn on VIRTIO_F_IOMMU_PLATFORM

References: bsc#1167075, bsc#1167445

We turn on device IOTLB via VIRTIO_F_IOMMU_PLATFORM unconditionally on
platform without IOMMU support. This can lead unnecessary IOTLB
transactions which will damage the performance.

Fixing this by check whether the device is backed by IOMMU and disable
device IOTLB.

Reported-by: Halil Pasic <pasic@linux.ibm.com>
Tested-by: Halil Pasic <pasic@linux.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.ibm.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20200302042454.24814-1-jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
(cherry picked from commit f7ef7e6e3ba6e994e070cc609eb154339d1c4a11)
Signed-off-by: Bruce Rogers <brogers@suse.com>
---
 hw/virtio/vhost.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index 4da0d5a6c5867325cb8cacab4894..554e76434ffaf2dc9ada0d4bdd7a 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -290,7 +290,14 @@ static int vhost_dev_has_iommu(struct vhost_dev *dev)
 {
     VirtIODevice *vdev = dev->vdev;
 
-    return virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM);
+    /*
+     * For vhost, VIRTIO_F_IOMMU_PLATFORM means the backend support
+     * incremental memory mapping API via IOTLB API. For platform that
+     * does not have IOMMU, there's no need to enable this feature
+     * which may cause unnecessary IOTLB miss/update trnasactions.
+     */
+    return vdev->dma_as != &address_space_memory &&
+           virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM);
 }
 
 static void *vhost_memory_map(struct vhost_dev *dev, hwaddr addr,
@@ -762,6 +769,9 @@ static int vhost_dev_set_features(struct vhost_dev *dev,
     if (enable_log) {
         features |= 0x1ULL << VHOST_F_LOG_ALL;
     }
+    if (!vhost_dev_has_iommu(dev)) {
+        features &= ~(0x1ULL << VIRTIO_F_IOMMU_PLATFORM);
+    }
     r = dev->vhost_ops->vhost_set_features(dev, features);
     if (r < 0) {
         VHOST_OPS_DEBUG("vhost_set_features failed");

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File vhost-correctly-turn-on-VIRTIO_F_IOMMU_P.patch of Package qemu.20755

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