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Re: [PATCH] virtio-net: prevent offloads reset on migration

From: Jason Wang
Subject: Re: [PATCH] virtio-net: prevent offloads reset on migration
Date: Thu, 10 Oct 2019 13:33:44 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 

On 2019/10/2 下午5:55, Dr. David Alan Gilbert wrote:

Copying in Stefan, Jason and Michael who know the virtio details

Dave

* Mikhail Sennikovsky (address@hidden) wrote:

Currently offloads disabled by guest via the VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET
command are not preserved on VM migration.
Instead all offloads reported by guest features (via VIRTIO_PCI_GUEST_FEATURES)
get enabled.
What happens is: first the VirtIONet::curr_guest_offloads gets restored and 
offloads
are getting set correctly:

  #0  qemu_set_offload (nc=0x555556a11400, csum=1, tso4=0, tso6=0, ecn=0, 
ufo=0) at net/net.c:474
  #1  virtio_net_apply_guest_offloads (n=0x555557701ca0) at 
hw/net/virtio-net.c:720
  #2  virtio_net_post_load_device (opaque=0x555557701ca0, version_id=11) at 
hw/net/virtio-net.c:2334
  #3  vmstate_load_state (f=0x5555569dc010, vmsd=0x555556577c80 
<vmstate_virtio_net_device>, opaque=0x555557701ca0, version_id=11)
      at migration/vmstate.c:168
  #4  virtio_load (vdev=0x555557701ca0, f=0x5555569dc010, version_id=11) at 
hw/virtio/virtio.c:2197
  #5  virtio_device_get (f=0x5555569dc010, opaque=0x555557701ca0, size=0, 
field=0x55555668cd00 <__compound_literal.5>) at hw/virtio/virtio.c:2036
  #6  vmstate_load_state (f=0x5555569dc010, vmsd=0x555556577ce0 
<vmstate_virtio_net>, opaque=0x555557701ca0, version_id=11) at 
migration/vmstate.c:143
  #7  vmstate_load (f=0x5555569dc010, se=0x5555578189e0) at 
migration/savevm.c:829
  #8  qemu_loadvm_section_start_full (f=0x5555569dc010, mis=0x5555569eee20) at 
migration/savevm.c:2211
  #9  qemu_loadvm_state_main (f=0x5555569dc010, mis=0x5555569eee20) at 
migration/savevm.c:2395
  #10 qemu_loadvm_state (f=0x5555569dc010) at migration/savevm.c:2467
  #11 process_incoming_migration_co (opaque=0x0) at migration/migration.c:449

However later on the features are getting restored, and offloads get reset to
everything supported by features:

  #0  qemu_set_offload (nc=0x555556a11400, csum=1, tso4=1, tso6=1, ecn=0, 
ufo=0) at net/net.c:474
  #1  virtio_net_apply_guest_offloads (n=0x555557701ca0) at 
hw/net/virtio-net.c:720
  #2  virtio_net_set_features (vdev=0x555557701ca0, features=5104441767) at 
hw/net/virtio-net.c:773
  #3  virtio_set_features_nocheck (vdev=0x555557701ca0, val=5104441767) at 
hw/virtio/virtio.c:2052
  #4  virtio_load (vdev=0x555557701ca0, f=0x5555569dc010, version_id=11) at 
hw/virtio/virtio.c:2220
  #5  virtio_device_get (f=0x5555569dc010, opaque=0x555557701ca0, size=0, 
field=0x55555668cd00 <__compound_literal.5>) at hw/virtio/virtio.c:2036
  #6  vmstate_load_state (f=0x5555569dc010, vmsd=0x555556577ce0 
<vmstate_virtio_net>, opaque=0x555557701ca0, version_id=11) at 
migration/vmstate.c:143
  #7  vmstate_load (f=0x5555569dc010, se=0x5555578189e0) at 
migration/savevm.c:829
  #8  qemu_loadvm_section_start_full (f=0x5555569dc010, mis=0x5555569eee20) at 
migration/savevm.c:2211
  #9  qemu_loadvm_state_main (f=0x5555569dc010, mis=0x5555569eee20) at 
migration/savevm.c:2395
  #10 qemu_loadvm_state (f=0x5555569dc010) at migration/savevm.c:2467
  #11 process_incoming_migration_co (opaque=0x0) at migration/migration.c:449

This patch fixes this by adding an extra argument to the set_features callback,
specifying whether the offloads are to be reset, and setting it to false
for the migration case.

Signed-off-by: Mikhail Sennikovsky <address@hidden>
---
  hw/display/virtio-gpu-base.c |  3 ++-
  hw/net/virtio-net.c          |  5 +++--
  hw/virtio/virtio.c           | 10 +++++-----
  include/hw/virtio/virtio.h   |  2 +-
  4 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/hw/display/virtio-gpu-base.c b/hw/display/virtio-gpu-base.c
index 55e0799..04d8a23 100644
--- a/hw/display/virtio-gpu-base.c
+++ b/hw/display/virtio-gpu-base.c
@@ -193,7 +193,8 @@ virtio_gpu_base_get_features(VirtIODevice *vdev, uint64_t 
features,
  }
static void 
-virtio_gpu_base_set_features(VirtIODevice *vdev, uint64_t features)
+virtio_gpu_base_set_features(VirtIODevice *vdev, uint64_t features,
+                               bool reset_offloads)



It's not good for e.g gpu to know anything about net.
How about checking runstate and do not call apply_guest_offload() in virtio_net_set_features() when in the state of migration? 

Thanks



  {
      static const uint32_t virgl = (1 << VIRTIO_GPU_F_VIRGL);
      VirtIOGPUBase *g = VIRTIO_GPU_BASE(vdev);
diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index b9e1cd7..5d108e5 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -743,7 +743,8 @@ static inline uint64_t 
virtio_net_supported_guest_offloads(VirtIONet *n)
      return virtio_net_guest_offloads_by_features(vdev->guest_features);
  }
-static void virtio_net_set_features(VirtIODevice *vdev, uint64_t features) 
+static void virtio_net_set_features(VirtIODevice *vdev, uint64_t features,
+                                        bool reset_offloads)
  {
      VirtIONet *n = VIRTIO_NET(vdev);
      int i;
@@ -767,7 +768,7 @@ static void virtio_net_set_features(VirtIODevice *vdev, 
uint64_t features)
      n->rsc6_enabled = virtio_has_feature(features, VIRTIO_NET_F_RSC_EXT) &&
          virtio_has_feature(features, VIRTIO_NET_F_GUEST_TSO6);
- if (n->has_vnet_hdr) { 
+    if (reset_offloads && n->has_vnet_hdr) {
          n->curr_guest_offloads =
              virtio_net_guest_offloads_by_features(features);
          virtio_net_apply_guest_offloads(n);
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index a94ea18..b89f7b0 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2042,14 +2042,14 @@ const VMStateInfo  virtio_vmstate_info = {
      .put = virtio_device_put,
  };
-static int virtio_set_features_nocheck(VirtIODevice *vdev, uint64_t val) 
+static int virtio_set_features_nocheck(VirtIODevice *vdev, uint64_t val, bool 
reset_offloads)
  {
      VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
      bool bad = (val & ~(vdev->host_features)) != 0;
val &= vdev->host_features; 
      if (k->set_features) {
-        k->set_features(vdev, val);
+        k->set_features(vdev, val, reset_offloads);
      }
      vdev->guest_features = val;
      return bad ? -1 : 0;
@@ -2065,7 +2065,7 @@ int virtio_set_features(VirtIODevice *vdev, uint64_t val)
      if (vdev->status & VIRTIO_CONFIG_S_FEATURES_OK) {
          return -EINVAL;
      }
-    ret = virtio_set_features_nocheck(vdev, val);
+    ret = virtio_set_features_nocheck(vdev, val, true);
      if (!ret) {
          if (virtio_vdev_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX)) {
              /* VIRTIO_RING_F_EVENT_IDX changes the size of the caches.  */
@@ -2217,14 +2217,14 @@ int virtio_load(VirtIODevice *vdev, QEMUFile *f, int 
version_id)
           * host_features.
           */
          uint64_t features64 = vdev->guest_features;
-        if (virtio_set_features_nocheck(vdev, features64) < 0) {
+        if (virtio_set_features_nocheck(vdev, features64, false) < 0) {
              error_report("Features 0x%" PRIx64 " unsupported. "
                           "Allowed features: 0x%" PRIx64,
                           features64, vdev->host_features);
              return -1;
          }
      } else {
-        if (virtio_set_features_nocheck(vdev, features) < 0) {
+        if (virtio_set_features_nocheck(vdev, features, false) < 0) {
              error_report("Features 0x%x unsupported. "
                           "Allowed features: 0x%" PRIx64,
                           features, vdev->host_features);
diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h
index b189788..fd8cac5 100644
--- a/include/hw/virtio/virtio.h
+++ b/include/hw/virtio/virtio.h
@@ -128,7 +128,7 @@ typedef struct VirtioDeviceClass {
                               uint64_t requested_features,
                               Error **errp);
      uint64_t (*bad_features)(VirtIODevice *vdev);
-    void (*set_features)(VirtIODevice *vdev, uint64_t val);
+    void (*set_features)(VirtIODevice *vdev, uint64_t val, bool 
reset_offloads);
      int (*validate_features)(VirtIODevice *vdev);
      void (*get_config)(VirtIODevice *vdev, uint8_t *config);
      void (*set_config)(VirtIODevice *vdev, const uint8_t *config);
--
2.7.4



--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
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