Re: [Qemu-devel] [PATCH v9] vhost: used_memslots refactoring

[Michael S. Tsirkin]

On Mon, Mar 05, 2018 at 05:12:49PM +0800, Jay Zhou wrote:
> Used_memslots is shared by vhost kernel and user, it is equal to
> dev->mem->nregions, which is correct for vhost kernel, but not for
> vhost user, the latter one uses memory regions that have file
> descriptor. E.g. a VM has a vhost-user NIC and 8(vhost user memslot
> upper limit) memory slots, it will be failed to hotplug a new DIMM
> device since vhost_has_free_slot() finds no free slot left. It
> should be successful if only part of memory slots have file
> descriptor, so setting used memslots for vhost-user and
> vhost-kernel respectively.


Below should go after ---

> v7 ... v9:
>  - rebased on the master
> v2 ... v6:
>  - delete the "used_memslots" global variable, and add it
>    for vhost-user and vhost-kernel separately
>  - refine the function, commit log
>  - used_memslots refactoring
> 
> Signed-off-by: Igor Mammedov <address@hidden>
> Signed-off-by: Jay Zhou <address@hidden>
> Signed-off-by: Liuzhe <address@hidden>

When built with clang this causes runtime warnings 
(during make check) about misaligned
access to structures.

The issue is that vhost_user_prepare_msg requests VhostUserMemory
which compiler assumes but is then used with a pointer into a packed structure -
where fields are not aligned.


> ---
>  hw/virtio/vhost-backend.c         | 15 +++++++-
>  hw/virtio/vhost-user.c            | 77 
> ++++++++++++++++++++++++++-------------
>  hw/virtio/vhost.c                 | 13 +++----
>  include/hw/virtio/vhost-backend.h |  6 ++-
>  4 files changed, 75 insertions(+), 36 deletions(-)
> 
> diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
> index 7f09efa..59def69 100644
> --- a/hw/virtio/vhost-backend.c
> +++ b/hw/virtio/vhost-backend.c
> @@ -15,6 +15,8 @@
>  #include "hw/virtio/vhost-backend.h"
>  #include "qemu/error-report.h"
>  
> +static unsigned int vhost_kernel_used_memslots;
> +
>  static int vhost_kernel_call(struct vhost_dev *dev, unsigned long int 
> request,
>                               void *arg)
>  {
> @@ -62,6 +64,11 @@ static int vhost_kernel_memslots_limit(struct vhost_dev 
> *dev)
>      return limit;
>  }
>  
> +static bool vhost_kernel_has_free_memslots(struct vhost_dev *dev)
> +{
> +    return vhost_kernel_used_memslots < vhost_kernel_memslots_limit(dev);
> +}
> +
>  static int vhost_kernel_net_set_backend(struct vhost_dev *dev,
>                                          struct vhost_vring_file *file)
>  {
> @@ -233,11 +240,16 @@ static void vhost_kernel_set_iotlb_callback(struct 
> vhost_dev *dev,
>          qemu_set_fd_handler((uintptr_t)dev->opaque, NULL, NULL, NULL);
>  }
>  
> +static void vhost_kernel_set_used_memslots(struct vhost_dev *dev)
> +{
> +    vhost_kernel_used_memslots = dev->mem->nregions;
> +}
> +
>  static const VhostOps kernel_ops = {
>          .backend_type = VHOST_BACKEND_TYPE_KERNEL,
>          .vhost_backend_init = vhost_kernel_init,
>          .vhost_backend_cleanup = vhost_kernel_cleanup,
> -        .vhost_backend_memslots_limit = vhost_kernel_memslots_limit,
> +        .vhost_backend_has_free_memslots = vhost_kernel_has_free_memslots,
>          .vhost_net_set_backend = vhost_kernel_net_set_backend,
>          .vhost_scsi_set_endpoint = vhost_kernel_scsi_set_endpoint,
>          .vhost_scsi_clear_endpoint = vhost_kernel_scsi_clear_endpoint,
> @@ -264,6 +276,7 @@ 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_set_used_memslots = vhost_kernel_set_used_memslots,
>  };
>  
>  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 41ff5cf..ef14249 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -163,6 +163,8 @@ static VhostUserMsg m __attribute__ ((unused));
>  /* The version of the protocol we support */
>  #define VHOST_USER_VERSION    (0x1)
>  
> +static bool vhost_user_free_memslots = true;
> +
>  struct vhost_user {
>      CharBackend *chr;
>      int slave_fd;
> @@ -330,12 +332,43 @@ static int vhost_user_set_log_base(struct vhost_dev 
> *dev, uint64_t base,
>      return 0;
>  }
>  
> +static int vhost_user_prepare_msg(struct vhost_dev *dev, VhostUserMemory 
> *mem,
> +                                  int *fds)
> +{
> +    int i, fd;
> +
> +    vhost_user_free_memslots = true;
> +    for (i = 0, mem->nregions = 0; i < dev->mem->nregions; ++i) {
> +        struct vhost_memory_region *reg = dev->mem->regions + i;
> +        ram_addr_t offset;
> +        MemoryRegion *mr;
> +
> +        assert((uintptr_t)reg->userspace_addr == reg->userspace_addr);
> +        mr = memory_region_from_host((void *)(uintptr_t)reg->userspace_addr,
> +                                     &offset);
> +        fd = memory_region_get_fd(mr);
> +        if (fd > 0) {
> +            if (mem->nregions == VHOST_MEMORY_MAX_NREGIONS) {
> +                vhost_user_free_memslots = false;
> +                return -1;
> +            }
> +
> +            mem->regions[mem->nregions].userspace_addr = reg->userspace_addr;
> +            mem->regions[mem->nregions].memory_size = reg->memory_size;
> +            mem->regions[mem->nregions].guest_phys_addr = 
> reg->guest_phys_addr;
> +            mem->regions[mem->nregions].mmap_offset = offset;
> +            fds[mem->nregions++] = fd;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
>  static int vhost_user_set_mem_table(struct vhost_dev *dev,
>                                      struct vhost_memory *mem)
>  {
>      int fds[VHOST_MEMORY_MAX_NREGIONS];
> -    int i, fd;
> -    size_t fd_num = 0;
> +    size_t fd_num;
>      bool reply_supported = virtio_has_feature(dev->protocol_features,
>                                                
> VHOST_USER_PROTOCOL_F_REPLY_ACK);
>  
> @@ -348,29 +381,12 @@ static int vhost_user_set_mem_table(struct vhost_dev 
> *dev,
>          msg.hdr.flags |= VHOST_USER_NEED_REPLY_MASK;
>      }
>  
> -    for (i = 0; i < dev->mem->nregions; ++i) {
> -        struct vhost_memory_region *reg = dev->mem->regions + i;
> -        ram_addr_t offset;
> -        MemoryRegion *mr;
> -
> -        assert((uintptr_t)reg->userspace_addr == reg->userspace_addr);
> -        mr = memory_region_from_host((void *)(uintptr_t)reg->userspace_addr,
> -                                     &offset);
> -        fd = memory_region_get_fd(mr);
> -        if (fd > 0) {
> -            if (fd_num == VHOST_MEMORY_MAX_NREGIONS) {
> -                error_report("Failed preparing vhost-user memory table msg");
> -                return -1;
> -            }
> -            msg.payload.memory.regions[fd_num].userspace_addr = 
> reg->userspace_addr;
> -            msg.payload.memory.regions[fd_num].memory_size  = 
> reg->memory_size;
> -            msg.payload.memory.regions[fd_num].guest_phys_addr = 
> reg->guest_phys_addr;
> -            msg.payload.memory.regions[fd_num].mmap_offset = offset;
> -            fds[fd_num++] = fd;
> -        }
> +    if (vhost_user_prepare_msg(dev, &msg.payload.memory, fds) < 0) {
> +        error_report("Failed preparing vhost-user memory table msg");
> +        return -1;
>      }
>  
> -    msg.payload.memory.nregions = fd_num;
> +    fd_num = msg.payload.memory.nregions;
>  
>      if (!fd_num) {
>          error_report("Failed initializing vhost-user memory map, "
> @@ -886,9 +902,9 @@ static int vhost_user_get_vq_index(struct vhost_dev *dev, 
> int idx)
>      return idx;
>  }
>  
> -static int vhost_user_memslots_limit(struct vhost_dev *dev)
> +static bool vhost_user_has_free_memslots(struct vhost_dev *dev)
>  {
> -    return VHOST_MEMORY_MAX_NREGIONS;
> +    return vhost_user_free_memslots;
>  }
>  
>  static bool vhost_user_requires_shm_log(struct vhost_dev *dev)
> @@ -1156,11 +1172,19 @@ vhost_user_crypto_close_session(struct vhost_dev 
> *dev, uint64_t session_id)
>      return 0;
>  }
>  
> +static void vhost_user_set_used_memslots(struct vhost_dev *dev)
> +{
> +    int fds[VHOST_MEMORY_MAX_NREGIONS];
> +    VhostUserMsg msg;
> +
> +    vhost_user_prepare_msg(dev, &msg.payload.memory, fds);

Oops.  This is something I don't understand.

Why is the message prepared here and then discarded?


> +}
> +
>  const VhostOps user_ops = {
>          .backend_type = VHOST_BACKEND_TYPE_USER,
>          .vhost_backend_init = vhost_user_init,
>          .vhost_backend_cleanup = vhost_user_cleanup,
> -        .vhost_backend_memslots_limit = vhost_user_memslots_limit,
> +        .vhost_backend_has_free_memslots = vhost_user_has_free_memslots,
>          .vhost_set_log_base = vhost_user_set_log_base,
>          .vhost_set_mem_table = vhost_user_set_mem_table,
>          .vhost_set_vring_addr = vhost_user_set_vring_addr,
> @@ -1184,6 +1208,7 @@ const VhostOps user_ops = {
>          .vhost_send_device_iotlb_msg = vhost_user_send_device_iotlb_msg,
>          .vhost_get_config = vhost_user_get_config,
>          .vhost_set_config = vhost_user_set_config,
> +        .vhost_set_used_memslots = vhost_user_set_used_memslots,
>          .vhost_crypto_create_session = vhost_user_crypto_create_session,
>          .vhost_crypto_close_session = vhost_user_crypto_close_session,
>  };
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index d8d0ef9..17262d2 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -44,20 +44,19 @@
>  static struct vhost_log *vhost_log;
>  static struct vhost_log *vhost_log_shm;
>  
> -static unsigned int used_memslots;
>  static QLIST_HEAD(, vhost_dev) vhost_devices =
>      QLIST_HEAD_INITIALIZER(vhost_devices);
>  
>  bool vhost_has_free_slot(void)
>  {
> -    unsigned int slots_limit = ~0U;
>      struct vhost_dev *hdev;
>  
>      QLIST_FOREACH(hdev, &vhost_devices, entry) {
> -        unsigned int r = hdev->vhost_ops->vhost_backend_memslots_limit(hdev);
> -        slots_limit = MIN(slots_limit, r);
> +        if (!hdev->vhost_ops->vhost_backend_has_free_memslots(hdev)) {
> +            return false;
> +        }
>      }
> -    return slots_limit > used_memslots;
> +    return true;
>  }
>  
>  static void vhost_dev_sync_region(struct vhost_dev *dev,
> @@ -446,7 +445,6 @@ static void vhost_commit(MemoryListener *listener)
>                         dev->n_mem_sections * sizeof dev->mem->regions[0];
>      dev->mem = g_realloc(dev->mem, regions_size);
>      dev->mem->nregions = dev->n_mem_sections;
> -    used_memslots = dev->mem->nregions;
>      for (i = 0; i < dev->n_mem_sections; i++) {
>          struct vhost_memory_region *cur_vmr = dev->mem->regions + i;
>          struct MemoryRegionSection *mrs = dev->mem_sections + i;
> @@ -458,6 +456,7 @@ static void vhost_commit(MemoryListener *listener)
>              mrs->offset_within_region;
>          cur_vmr->flags_padding   = 0;
>      }
> +    dev->vhost_ops->vhost_set_used_memslots(dev);
>  
>      if (!dev->started) {
>          goto out;
> @@ -1202,7 +1201,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
>      memory_listener_register(&hdev->memory_listener, &address_space_memory);
>      QLIST_INSERT_HEAD(&vhost_devices, hdev, entry);
>  
> -    if (used_memslots > hdev->vhost_ops->vhost_backend_memslots_limit(hdev)) 
> {
> +    if (!hdev->vhost_ops->vhost_backend_has_free_memslots(hdev)) {
>          error_report("vhost backend memory slots limit is less"
>                  " than current number of present memory slots");
>          r = -1;
> diff --git a/include/hw/virtio/vhost-backend.h 
> b/include/hw/virtio/vhost-backend.h
> index 5dac61f..ff06c2d 100644
> --- a/include/hw/virtio/vhost-backend.h
> +++ b/include/hw/virtio/vhost-backend.h
> @@ -36,7 +36,7 @@ struct vhost_iotlb_msg;
>  
>  typedef int (*vhost_backend_init)(struct vhost_dev *dev, void *opaque);
>  typedef int (*vhost_backend_cleanup)(struct vhost_dev *dev);
> -typedef int (*vhost_backend_memslots_limit)(struct vhost_dev *dev);
> +typedef bool (*vhost_backend_has_free_memslots)(struct vhost_dev *dev);
>  
>  typedef int (*vhost_net_set_backend_op)(struct vhost_dev *dev,
>                                  struct vhost_vring_file *file);
> @@ -94,6 +94,7 @@ typedef int (*vhost_set_config_op)(struct vhost_dev *dev, 
> const uint8_t *data,
>                                     uint32_t flags);
>  typedef int (*vhost_get_config_op)(struct vhost_dev *dev, uint8_t *config,
>                                     uint32_t config_len);
> +typedef void (*vhost_set_used_memslots_op)(struct vhost_dev *dev);
>  
>  typedef int (*vhost_crypto_create_session_op)(struct vhost_dev *dev,
>                                                void *session_info,
> @@ -105,7 +106,7 @@ typedef struct VhostOps {
>      VhostBackendType backend_type;
>      vhost_backend_init vhost_backend_init;
>      vhost_backend_cleanup vhost_backend_cleanup;
> -    vhost_backend_memslots_limit vhost_backend_memslots_limit;
> +    vhost_backend_has_free_memslots vhost_backend_has_free_memslots;
>      vhost_net_set_backend_op vhost_net_set_backend;
>      vhost_net_set_mtu_op vhost_net_set_mtu;
>      vhost_scsi_set_endpoint_op vhost_scsi_set_endpoint;
> @@ -136,6 +137,7 @@ typedef struct VhostOps {
>      vhost_send_device_iotlb_msg_op vhost_send_device_iotlb_msg;
>      vhost_get_config_op vhost_get_config;
>      vhost_set_config_op vhost_set_config;
> +    vhost_set_used_memslots_op vhost_set_used_memslots;
>      vhost_crypto_create_session_op vhost_crypto_create_session;
>      vhost_crypto_close_session_op vhost_crypto_close_session;
>  } VhostOps;
> -- 
> 1.8.3.1
>