Re: [PATCH] vhost-user: add separate memslot counter for vhost-user

[Igor Mammedov <imammedo@redhat.com>]

On Mon, 28 Sep 2020 21:17:31 +0800
Jiajun Chen <chenjiajun8@huawei.com> wrote:

> Used_memslots is equal to dev->mem->nregions now, it is true for
> vhost kernel, but not for vhost user, which uses the memory regions
> that have file descriptor. In fact, not all of the memory regions
> have file descriptor.
> It is usefully in some scenarios, e.g. used_memslots is 8, and only
> 5 memory slots can be used by vhost user, it is failed to hot plug
> a new memory RAM because vhost_has_free_slot just returned false,
> but we can hot plug it safely in fact.

I had an impression that all guest RAM has to be shared with vhost,
so combination of anon and fd based RAM couldn't work.
Am I wrong?

> 
> --
> ChangeList:
> v3:
> -make used_memslots a member of struct vhost_dev instead of a global static value
it's global resource, so why?

> 
> v2:
> -eliminating useless used_memslots_exceeded variable and used_memslots_is_exceeded() API
> 
> v1:
> -vhost-user: add separate memslot counter for vhost-user
> 
> Signed-off-by: Jiajun Chen <chenjiajun8@huawei.com>
> Signed-off-by: Jianjay Zhou <jianjay.zhou@huawei.com>
> ---
>  hw/virtio/vhost-backend.c         | 12 ++++++++++
>  hw/virtio/vhost-user.c            | 25 +++++++++++++++++++++
>  hw/virtio/vhost.c                 | 37 +++++++++++++++++++++++--------
>  include/hw/virtio/vhost-backend.h |  5 +++++
>  include/hw/virtio/vhost.h         |  1 +
>  net/vhost-user.c                  |  7 ++++++
>  6 files changed, 78 insertions(+), 9 deletions(-)
> 
> diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
> index 782b1d67d9..7016f23ec5 100644
> --- a/hw/virtio/vhost-backend.c
> +++ b/hw/virtio/vhost-backend.c
> @@ -238,6 +238,16 @@ 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)
> +{
> +    dev->used_memslots = dev->mem->nregions;
> +}
> +
> +static unsigned int vhost_kernel_get_used_memslots(struct vhost_dev *dev)
> +{
> +    return dev->used_memslots;
> +}
> +
>  static const VhostOps kernel_ops = {
>          .backend_type = VHOST_BACKEND_TYPE_KERNEL,
>          .vhost_backend_init = vhost_kernel_init,
> @@ -269,6 +279,8 @@ 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_set_used_memslots = vhost_kernel_set_used_memslots,
> +        .vhost_get_used_memslots = vhost_kernel_get_used_memslots,
>  };
>  #endif
>  
> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
> index 31231218dc..5dea64d8a8 100644
> --- a/hw/virtio/vhost-user.c
> +++ b/hw/virtio/vhost-user.c
> @@ -2354,6 +2354,29 @@ void vhost_user_cleanup(VhostUserState *user)
>      user->chr = NULL;
>  }
>  
> +static void vhost_user_set_used_memslots(struct vhost_dev *dev)
> +{
> +    int i;
> +    dev->used_memslots = 0;
> +
> +    for (i = 0; i < dev->mem->nregions; ++i) {
> +        struct vhost_memory_region *reg = dev->mem->regions + i;
> +        ram_addr_t offset;
> +        MemoryRegion *mr;
> +        int fd;
> +
> +        mr = vhost_user_get_mr_data(reg->userspace_addr, &offset, &fd);
> +        if (mr && fd > 0) {
> +            dev->used_memslots++;
> +        }
> +    }
> +}
> +
> +static unsigned int vhost_user_get_used_memslots(struct vhost_dev *dev)
> +{
> +    return dev->used_memslots;
> +}
> +
>  const VhostOps user_ops = {
>          .backend_type = VHOST_BACKEND_TYPE_USER,
>          .vhost_backend_init = vhost_user_backend_init,
> @@ -2387,4 +2410,6 @@ const VhostOps user_ops = {
>          .vhost_backend_mem_section_filter = vhost_user_mem_section_filter,
>          .vhost_get_inflight_fd = vhost_user_get_inflight_fd,
>          .vhost_set_inflight_fd = vhost_user_set_inflight_fd,
> +        .vhost_set_used_memslots = vhost_user_set_used_memslots,
> +        .vhost_get_used_memslots = vhost_user_get_used_memslots,
>  };
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 1a1384e7a6..98b967669b 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -45,20 +45,20 @@
>  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_get_used_memslots(hdev) >=
> +            hdev->vhost_ops->vhost_backend_memslots_limit(hdev)) {
> +            return false;
> +        }
>      }
> -    return slots_limit > used_memslots;
> +    return true;
>  }
>  
>  static void vhost_dev_sync_region(struct vhost_dev *dev,
> @@ -502,7 +502,6 @@ 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;
> @@ -678,6 +677,7 @@ static void vhost_region_add_section(struct vhost_dev *dev,
>          dev->tmp_sections[dev->n_tmp_sections - 1].fv = NULL;
>          memory_region_ref(section->mr);
>      }
> +    dev->vhost_ops->vhost_set_used_memslots(dev);
>  }
>  
>  /* Used for both add and nop callbacks */
> @@ -693,6 +693,17 @@ static void vhost_region_addnop(MemoryListener *listener,
>      vhost_region_add_section(dev, section);
>  }
>  
> +static void vhost_region_del(MemoryListener *listener,
> +                             MemoryRegionSection *section)
> +{
> +    struct vhost_dev *dev = container_of(listener, struct vhost_dev,
> +                                         memory_listener);
> +    if (!vhost_section(dev, section)) {
> +        return;
> +    }
> +    dev->vhost_ops->vhost_set_used_memslots(dev);
> +}
> +
>  static void vhost_iommu_unmap_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
>  {
>      struct vhost_iommu *iommu = container_of(n, struct vhost_iommu, n);
> @@ -1300,6 +1311,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
>      hdev->memory_listener = (MemoryListener) {
>          .begin = vhost_begin,
>          .commit = vhost_commit,
> +        .region_del = vhost_region_del,
>          .region_add = vhost_region_addnop,
>          .region_nop = vhost_region_addnop,
>          .log_start = vhost_log_start,
> @@ -1346,9 +1358,16 @@ 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)) {
> -        error_report("vhost backend memory slots limit is less"
> -                " than current number of present memory slots");
> +    /*
> +     * If we started a VM without any vhost device,
> +     * for the first time vhost device hot-plug
> +     * (vhost_get_used_memslots is always 0),
> +     * so it needs to double check here.
> +     */
> +    if (hdev->vhost_ops->vhost_get_used_memslots(hdev) >
> +        hdev->vhost_ops->vhost_backend_memslots_limit(hdev)) {
> +        error_report("vhost backend memory slots limit is less than"
> +                     " current number of present memory slots");
>          r = -1;
>          if (busyloop_timeout) {
>              goto fail_busyloop;
> diff --git a/include/hw/virtio/vhost-backend.h b/include/hw/virtio/vhost-backend.h
> index 8825bd278f..6569c95a43 100644
> --- a/include/hw/virtio/vhost-backend.h
> +++ b/include/hw/virtio/vhost-backend.h
> @@ -124,6 +124,9 @@ typedef int (*vhost_get_device_id_op)(struct vhost_dev *dev, uint32_t *dev_id);
>  
>  typedef bool (*vhost_force_iommu_op)(struct vhost_dev *dev);
>  
> +typedef void (*vhost_set_used_memslots_op)(struct vhost_dev *dev);
> +typedef unsigned int (*vhost_get_used_memslots_op)(struct vhost_dev *dev);
> +
>  typedef struct VhostOps {
>      VhostBackendType backend_type;
>      vhost_backend_init vhost_backend_init;
> @@ -168,6 +171,8 @@ typedef struct VhostOps {
>      vhost_vq_get_addr_op  vhost_vq_get_addr;
>      vhost_get_device_id_op vhost_get_device_id;
>      vhost_force_iommu_op vhost_force_iommu;
> +    vhost_set_used_memslots_op vhost_set_used_memslots;
> +    vhost_get_used_memslots_op vhost_get_used_memslots;
>  } VhostOps;
>  
>  extern const VhostOps user_ops;
> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> index 767a95ec0b..5ded21f86d 100644
> --- a/include/hw/virtio/vhost.h
> +++ b/include/hw/virtio/vhost.h
> @@ -90,6 +90,7 @@ struct vhost_dev {
>      QLIST_HEAD(, vhost_iommu) iommu_list;
>      IOMMUNotifier n;
>      const VhostDevConfigOps *config_ops;
> +    unsigned int used_memslots;
>  };
>  
>  struct vhost_net {
> diff --git a/net/vhost-user.c b/net/vhost-user.c
> index 17532daaf3..7e93955537 100644
> --- a/net/vhost-user.c
> +++ b/net/vhost-user.c
> @@ -20,6 +20,7 @@
>  #include "qemu/error-report.h"
>  #include "qemu/option.h"
>  #include "trace.h"
> +#include "include/hw/virtio/vhost.h"
>  
>  typedef struct NetVhostUserState {
>      NetClientState nc;
> @@ -347,6 +348,12 @@ static int net_vhost_user_init(NetClientState *peer, const char *device,
>          qemu_chr_fe_set_handlers(&s->chr, NULL, NULL,
>                                   net_vhost_user_event, NULL, nc0->name, NULL,
>                                   true);
> +
> +        if (!vhost_has_free_slot()) {
> +            error_report("used memslots exceeded the backend limit, quit "
> +                         "loop");
> +            goto err;
> +        }
>      } while (!s->started);
>  
>      assert(s->vhost_net);