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


From: Zhoujian (jay)
Subject: Re: [Qemu-devel] [PATCH v9] vhost: used_memslots refactoring
Date: Tue, 20 Mar 2018 02:09:34 +0000

Hi Michael,

> -----Original Message-----
> From: Michael S. Tsirkin [mailto:address@hidden
> Sent: Tuesday, March 20, 2018 9:34 AM
> To: Zhoujian (jay) <address@hidden>
> Cc: address@hidden; address@hidden; Huangweidong (C)
> <address@hidden>; wangxin (U) <address@hidden>; Gonglei
> (Arei) <address@hidden>; Liuzhe (Ahriy, Euler) <address@hidden>
> Subject: Re: [PATCH v9] vhost: used_memslots refactoring
> 
> 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 ---

Thanks for reminding.

> 
> > 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.

Sorry I missed the patch you have sent to fix the alignment, I have replied
to that thread.

> 
> 
> > ---
> >  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?
> 

The purpose of vhost_user_set_used_memslots() is to set the boolean value
of vhost_user_free_memslots, which indicating whether there're free memeslots
for vhost user. Since there're code duplicating inside 
vhost_user_set_used_memslots()
and vhost_user_set_mem_table(), Igor suggested that we could create a new 
function
to avoid duplicating.
Here, the value of VhostUserMsg is not needed by the caller 
vhost_user_set_used_memslots(),
so we just discarded.

Regards,
Jay

> 
> > +}
> > +
> >  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
> >



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