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Re: [Qemu-devel] [PATCH v9] vhost: used_memslots refactoring
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From: |
Michael S. Tsirkin |
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Subject: |
Re: [Qemu-devel] [PATCH v9] vhost: used_memslots refactoring |
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Date: |
Tue, 20 Mar 2018 04:51:01 +0200 |
On Tue, Mar 20, 2018 at 02:09:34AM +0000, Zhoujian (jay) wrote:
> 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
I think I misunderstood the meaning of that variable.
It seems to be set when there are more slots than
supported.
What vhost_user_free_memslots implies is that it is
set when there are no free slots, even if existing
config fits.
A better name would be vhost_user_out_of_memslots maybe?
And I missed the fact that it (as well as the prepare call)
can actually fail when out of slots.
Shouldn't it return status too?
> >
> > > +}
> > > +
> > > 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
> > >