[Qemu-devel] [RFC] vhost-user: introduce F_NEED_ALL_IOTLB protocol feature

[Tiwei Bie]

This patch introduces VHOST_USER_PROTOCOL_F_NEED_ALL_IOTLB
feature for vhost-user. By default, vhost-user backend needs
to query the IOTLBs from QEMU after meeting unknown IOVAs.
With this protocol feature negotiated, QEMU will provide all
the IOTLBs to vhost-user backend without waiting for the
queries from backend. This is helpful when using a hardware
accelerator which is not able to handle unknown IOVAs at the
vhost-user backend.

Signed-off-by: Tiwei Bie <address@hidden>
---
The idea of this patch is to let QEMU push all the IOTLBs
to vhost-user backend without waiting for the queries from
the backend. Because hardware accelerator at the vhost-user
backend may not be able to handle unknown IOVAs.

This is just a RFC for now. It seems that, it doesn't work
as expected when guest is using kernel driver (To handle
this case, it seems that some RAM regions' events also need
to be listened). Any comments would be appreciated! Thanks!

 docs/interop/vhost-user.txt       |  9 ++++++++
 hw/virtio/vhost-backend.c         |  7 ++++++
 hw/virtio/vhost-user.c            |  8 +++++++
 hw/virtio/vhost.c                 | 47 ++++++++++++++++++++++++++++++++++++---
 include/hw/virtio/vhost-backend.h |  3 +++
 5 files changed, 71 insertions(+), 3 deletions(-)

diff --git a/docs/interop/vhost-user.txt b/docs/interop/vhost-user.txt
index 534caab18a..73e07f9dad 100644
--- a/docs/interop/vhost-user.txt
+++ b/docs/interop/vhost-user.txt
@@ -380,6 +380,7 @@ Protocol features
 #define VHOST_USER_PROTOCOL_F_CRYPTO_SESSION 7
 #define VHOST_USER_PROTOCOL_F_PAGEFAULT      8
 #define VHOST_USER_PROTOCOL_F_CONFIG         9
+#define VHOST_USER_PROTOCOL_F_NEED_ALL_IOTLB 10
 
 Master message types
 --------------------
@@ -797,3 +798,11 @@ resilient for selective requests.
 For the message types that already solicit a reply from the client, the
 presence of VHOST_USER_PROTOCOL_F_REPLY_ACK or need_reply bit being set brings
 no behavioural change. (See the 'Communication' section for details.)
+
+VHOST_USER_PROTOCOL_F_NEED_ALL_IOTLB
+------------------------------------
+By default, vhost-user backend needs to query the IOTLBs from QEMU after
+meeting unknown IOVAs. With this protocol feature negotiated, QEMU will
+provide all the IOTLBs to vhost backend without waiting for the queries
+from backend. This is helpful when using a hardware accelerator which is
+not able to handle unknown IOVAs at the vhost-user backend.
diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
index 7f09efab8b..d72994e9a5 100644
--- a/hw/virtio/vhost-backend.c
+++ b/hw/virtio/vhost-backend.c
@@ -233,6 +233,11 @@ static void vhost_kernel_set_iotlb_callback(struct 
vhost_dev *dev,
         qemu_set_fd_handler((uintptr_t)dev->opaque, NULL, NULL, NULL);
 }
 
+static bool vhost_kernel_need_all_device_iotlb(struct vhost_dev *dev)
+{
+    return false;
+}
+
 static const VhostOps kernel_ops = {
         .backend_type = VHOST_BACKEND_TYPE_KERNEL,
         .vhost_backend_init = vhost_kernel_init,
@@ -264,6 +269,8 @@ static const VhostOps kernel_ops = {
 #endif /* CONFIG_VHOST_VSOCK */
         .vhost_set_iotlb_callback = vhost_kernel_set_iotlb_callback,
         .vhost_send_device_iotlb_msg = vhost_kernel_send_device_iotlb_msg,
+        .vhost_backend_need_all_device_iotlb =
+                                vhost_kernel_need_all_device_iotlb,
 };
 
 int vhost_set_backend_type(struct vhost_dev *dev, VhostBackendType 
backend_type)
diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
index 38da8692bb..30e0b1c13b 100644
--- a/hw/virtio/vhost-user.c
+++ b/hw/virtio/vhost-user.c
@@ -47,6 +47,7 @@ enum VhostUserProtocolFeature {
     VHOST_USER_PROTOCOL_F_CRYPTO_SESSION = 7,
     VHOST_USER_PROTOCOL_F_PAGEFAULT = 8,
     VHOST_USER_PROTOCOL_F_CONFIG = 9,
+    VHOST_USER_PROTOCOL_F_NEED_ALL_IOTLB = 10,
     VHOST_USER_PROTOCOL_F_MAX
 };
 
@@ -1581,6 +1582,12 @@ vhost_user_crypto_close_session(struct vhost_dev *dev, 
uint64_t session_id)
     return 0;
 }
 
+static bool vhost_user_need_all_device_iotlb(struct vhost_dev *dev)
+{
+    return virtio_has_feature(dev->protocol_features,
+                              VHOST_USER_PROTOCOL_F_NEED_ALL_IOTLB);
+}
+
 const VhostOps user_ops = {
         .backend_type = VHOST_BACKEND_TYPE_USER,
         .vhost_backend_init = vhost_user_init,
@@ -1611,4 +1618,5 @@ const VhostOps user_ops = {
         .vhost_set_config = vhost_user_set_config,
         .vhost_crypto_create_session = vhost_user_crypto_create_session,
         .vhost_crypto_close_session = vhost_user_crypto_close_session,
+        .vhost_backend_need_all_device_iotlb = 
vhost_user_need_all_device_iotlb,
 };
diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
index f51bf573d5..70922ee998 100644
--- a/hw/virtio/vhost.c
+++ b/hw/virtio/vhost.c
@@ -48,6 +48,9 @@ static unsigned int used_memslots;
 static QLIST_HEAD(, vhost_dev) vhost_devices =
     QLIST_HEAD_INITIALIZER(vhost_devices);
 
+static int vhost_memory_region_lookup(struct vhost_dev *hdev, uint64_t gpa,
+                                      uint64_t *uaddr, uint64_t *len);
+
 bool vhost_has_free_slot(void)
 {
     unsigned int slots_limit = ~0U;
@@ -634,12 +637,39 @@ static void vhost_region_addnop(MemoryListener *listener,
     vhost_region_add_section(dev, section);
 }
 
-static void vhost_iommu_unmap_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
+static void vhost_iommu_map_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
 {
     struct vhost_iommu *iommu = container_of(n, struct vhost_iommu, n);
     struct vhost_dev *hdev = iommu->hdev;
     hwaddr iova = iotlb->iova + iommu->iommu_offset;
 
+    if ((iotlb->perm & IOMMU_RW) != IOMMU_NONE) {
+        uint64_t uaddr, len;
+
+        rcu_read_lock();
+
+        if (iotlb->target_as != NULL) {
+            if (vhost_memory_region_lookup(hdev, iotlb->translated_addr,
+                        &uaddr, &len)) {
+                error_report("Fail to lookup the translated address "
+                        "%"PRIx64, iotlb->translated_addr);
+                goto out;
+            }
+
+            len = MIN(iotlb->addr_mask + 1, len);
+            iova = iova & ~iotlb->addr_mask;
+
+            if (vhost_backend_update_device_iotlb(hdev, iova, uaddr,
+                                                  len, iotlb->perm)) {
+                error_report("Fail to update device iotlb");
+                goto out;
+            }
+        }
+out:
+        rcu_read_unlock();
+        return;
+    }
+
     if (vhost_backend_invalidate_device_iotlb(hdev, iova,
                                               iotlb->addr_mask + 1)) {
         error_report("Fail to invalidate device iotlb");
@@ -652,6 +682,7 @@ static void vhost_iommu_region_add(MemoryListener *listener,
     struct vhost_dev *dev = container_of(listener, struct vhost_dev,
                                          iommu_listener);
     struct vhost_iommu *iommu;
+    IOMMUNotifierFlag flags;
     Int128 end;
 
     if (!memory_region_is_iommu(section->mr)) {
@@ -662,8 +693,15 @@ static void vhost_iommu_region_add(MemoryListener 
*listener,
     end = int128_add(int128_make64(section->offset_within_region),
                      section->size);
     end = int128_sub(end, int128_one());
-    iommu_notifier_init(&iommu->n, vhost_iommu_unmap_notify,
-                        IOMMU_NOTIFIER_UNMAP,
+
+    if (dev->vhost_ops->vhost_backend_need_all_device_iotlb(dev)) {
+        flags = IOMMU_NOTIFIER_ALL;
+    } else {
+        flags = IOMMU_NOTIFIER_UNMAP;
+    }
+
+    iommu_notifier_init(&iommu->n, vhost_iommu_map_notify,
+                        flags,
                         section->offset_within_region,
                         int128_get64(end));
     iommu->mr = section->mr;
@@ -673,6 +711,9 @@ static void vhost_iommu_region_add(MemoryListener *listener,
     memory_region_register_iommu_notifier(section->mr, &iommu->n);
     QLIST_INSERT_HEAD(&dev->iommu_list, iommu, iommu_next);
     /* TODO: can replay help performance here? */
+    if (flags == IOMMU_NOTIFIER_ALL) {
+        memory_region_iommu_replay(IOMMU_MEMORY_REGION(iommu->mr), &iommu->n);
+    }
 }
 
 static void vhost_iommu_region_del(MemoryListener *listener,
diff --git a/include/hw/virtio/vhost-backend.h 
b/include/hw/virtio/vhost-backend.h
index 5dac61f9ea..602fd987a4 100644
--- a/include/hw/virtio/vhost-backend.h
+++ b/include/hw/virtio/vhost-backend.h
@@ -101,6 +101,8 @@ typedef int (*vhost_crypto_create_session_op)(struct 
vhost_dev *dev,
 typedef int (*vhost_crypto_close_session_op)(struct vhost_dev *dev,
                                              uint64_t session_id);
 
+typedef bool (*vhost_backend_need_all_device_iotlb_op)(struct vhost_dev *dev);
+
 typedef struct VhostOps {
     VhostBackendType backend_type;
     vhost_backend_init vhost_backend_init;
@@ -138,6 +140,7 @@ typedef struct VhostOps {
     vhost_set_config_op vhost_set_config;
     vhost_crypto_create_session_op vhost_crypto_create_session;
     vhost_crypto_close_session_op vhost_crypto_close_session;
+    vhost_backend_need_all_device_iotlb_op vhost_backend_need_all_device_iotlb;
 } VhostOps;
 
 extern const VhostOps user_ops;
-- 
2.11.0