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Re: [PATCH] IOMMU and ATS not supported by vhost-user filesystem.

From: Leonardo Augusto Guimarães Garcia
Subject: Re: [PATCH] IOMMU and ATS not supported by vhost-user filesystem.
Date: Wed, 17 Feb 2021 14:07:16 -0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0

On 1/27/21 8:19 AM, Stefan Hajnoczi wrote:
On Tue, Jan 26, 2021 at 03:23:38PM -0300, lagarcia@linux.ibm.com wrote:
From: Leonardo Garcia <lagarcia@br.ibm.com>

Currently, as IOMMU and ATS are not supported, if a user mistakenly set
any of them and tries to mount the vhost-user filesystem inside the
guest, whenever the user tries to access the mount point, the system
will hang forever.

Signed-off-by: Leonardo Garcia <lagarcia@br.ibm.com>
  hw/virtio/vhost-user-fs-pci.c | 7 +++++++
  hw/virtio/vhost-user-fs.c     | 5 +++++
  2 files changed, 12 insertions(+)

diff --git a/hw/virtio/vhost-user-fs-pci.c b/hw/virtio/vhost-user-fs-pci.c
index 2ed8492b3f..564d1fd108 100644
--- a/hw/virtio/vhost-user-fs-pci.c
+++ b/hw/virtio/vhost-user-fs-pci.c
@@ -11,6 +11,8 @@
   * top-level directory.
+#include "qemu/osdep.h"
+#include "qapi/error.h"
  #include "qemu/osdep.h"
  #include "hw/qdev-properties.h"
  #include "hw/virtio/vhost-user-fs.h"
@@ -45,6 +47,11 @@ static void vhost_user_fs_pci_realize(VirtIOPCIProxy 
*vpci_dev, Error **errp)
          vpci_dev->nvectors = dev->vdev.conf.num_request_queues + 2;
+ if (vpci_dev->flags & VIRTIO_PCI_FLAG_ATS) {
+        error_setg(errp, "ATS is currently not supported with 
+        return;
+    }
Why is this check needed in addition to VIRTIO_F_IOMMU_PLATFORM?

What needs to be added to support ATS?

As I am working on v2 for this patch, I revisited this. There is no need for this check. ATS works fine. The only problem is with the iommu_platform flag.



      qdev_realize(vdev, BUS(&vpci_dev->bus), errp);
diff --git a/hw/virtio/vhost-user-fs.c b/hw/virtio/vhost-user-fs.c
index ac4fc34b36..914d68b3ee 100644
--- a/hw/virtio/vhost-user-fs.c
+++ b/hw/virtio/vhost-user-fs.c
@@ -203,6 +203,11 @@ static void vuf_device_realize(DeviceState *dev, Error 
+ if (virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM)) {
+        error_setg(errp, "IOMMU is currently not supported with 
+        return;
+    }
      if (!vhost_user_init(&fs->vhost_user, &fs->conf.chardev, errp)) {
I thought IOMMU support depends on the vhost-user device backend (e.g.
virtiofsd), so the vhost-user backend should participate in advertising
this feature.

Perhaps the check should be:

     ret = vhost_dev_init(&fs->vhost_dev, &fs->vhost_user,
                          VHOST_BACKEND_TYPE_USER, 0);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "vhost_dev_init failed");
         goto err_virtio;
+   if (virtio_host_has_feature(vdev, VIRTIO_F_IOMMU_PLATFORM) &&
+       !(fs->vhost_dev.hdev_features & (1ull << VIRTIO_F_IOMMU_PLATFORM))) {
+       error_setg(errp, "IOMMU is not supported by the vhost-user device 
+       goto err_iommu_needed;
+   }

Also, can this logic be made generic for all vhost-user devices? It's
not really specific to vhost-user-fs.


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