Re: [Qemu-devel] [PATCH 1/2] vhost: add vhost_has_free_slot() interface

[Igor Mammedov]

On Wed, 29 Jul 2015 13:20:24 +0300
"Michael S. Tsirkin" <address@hidden> wrote:

> On Mon, Jul 20, 2015 at 03:49:29PM +0200, Igor Mammedov wrote:
> > it will allow for other parts of QEMU check if it's safe
> > to map memory region during hotplug/runtime.
> > That way hotplug path will have a chance to cancel
> > hotplug operation instead of crashing in vhost_commit().
> > 
> > Signed-off-by: Igor Mammedov <address@hidden>
> > ---
> >  hw/virtio/vhost-backend.c         | 23 ++++++++++++++++++++++-
> >  hw/virtio/vhost-user.c            |  8 +++++++-
> >  hw/virtio/vhost.c                 | 21 +++++++++++++++++++++
> >  include/hw/virtio/vhost-backend.h |  2 ++
> >  include/hw/virtio/vhost.h         |  1 +
> >  stubs/Makefile.objs               |  1 +
> >  stubs/vhost.c                     |  6 ++++++
> >  7 files changed, 60 insertions(+), 2 deletions(-)
> >  create mode 100644 stubs/vhost.c
> > 
> > diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
> > index 4d68a27..46fa707 100644
> > --- a/hw/virtio/vhost-backend.c
> > +++ b/hw/virtio/vhost-backend.c
> > @@ -11,6 +11,7 @@
> >  #include "hw/virtio/vhost.h"
> >  #include "hw/virtio/vhost-backend.h"
> >  #include "qemu/error-report.h"
> > +#include "linux/vhost.h"
> >  
> >  #include <sys/ioctl.h>
> >  
> > @@ -42,11 +43,31 @@ static int vhost_kernel_cleanup(struct vhost_dev *dev)
> >      return close(fd);
> >  }
> >  
> > +static int vhost_kernel_memslots_limit(struct vhost_dev *dev)
> > +{
> > +    int limit;
> > +    int s = offsetof(struct vhost_memory, regions);
> > +    struct vhost_memory *mem = g_malloc0(s);
> > +
> > +    assert(dev->mem->nregions);
> > +    do {
> > +        s += sizeof mem->regions[0];
> > +        mem = g_realloc(mem, s);
> > +        mem->regions[mem->nregions] = dev->mem->regions[0];
> > +        mem->nregions++;
> > +    } while (vhost_kernel_call(dev, VHOST_SET_MEM_TABLE, mem) != -1);
> > +    limit = mem->nregions - 1 > 0 ? mem->nregions - 1 : 0;
> > +    g_free(mem);
> > +
> > +    return limit;
> > +}
> > +
> 
> I don't like this probing much: if one clocks the size up
> significantly, this will slow down the box trying
> to allocate kernel memory for no real reason.
> 
> I'd rather check /sys/modules/vhost/parameters/max_mem_regions.
> If not there, assume 64.
I'll respin with this suggestion even if it's a bit ugly.
In addition to it we can add IOCTL interface to detect limit later
when kernel side would be ready for it.


> 
> >  static const VhostOps kernel_ops = {
> >          .backend_type = VHOST_BACKEND_TYPE_KERNEL,
> >          .vhost_call = vhost_kernel_call,
> >          .vhost_backend_init = vhost_kernel_init,
> > -        .vhost_backend_cleanup = vhost_kernel_cleanup
> > +        .vhost_backend_cleanup = vhost_kernel_cleanup,
> > +        .vhost_backend_memslots_limit = vhost_kernel_memslots_limit
> >  };
> >  
> >  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 d6f2163..0487809 100644
> > --- a/hw/virtio/vhost-user.c
> > +++ b/hw/virtio/vhost-user.c
> > @@ -352,9 +352,15 @@ static int vhost_user_cleanup(struct vhost_dev *dev)
> >      return 0;
> >  }
> >  
> > +static int vhost_user_memslots_limit(struct vhost_dev *dev)
> > +{
> > +    return VHOST_MEMORY_MAX_NREGIONS;
> > +}
> > +
> >  const VhostOps user_ops = {
> >          .backend_type = VHOST_BACKEND_TYPE_USER,
> >          .vhost_call = vhost_user_call,
> >          .vhost_backend_init = vhost_user_init,
> > -        .vhost_backend_cleanup = vhost_user_cleanup
> > +        .vhost_backend_cleanup = vhost_user_cleanup,
> > +        .vhost_backend_memslots_limit = vhost_user_memslots_limit
> >          };
> > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> > index 2712c6f..e964004 100644
> > --- a/hw/virtio/vhost.c
> > +++ b/hw/virtio/vhost.c
> > @@ -26,6 +26,18 @@
> >  
> >  static struct vhost_log *vhost_log;
> >  
> > +static int used_memslots;
> > +static int memslots_limit = -1;
> > +
> > +bool vhost_has_free_slot(void)
> > +{
> > +    if (memslots_limit >= 0) {
> > +        return memslots_limit > used_memslots;
> > +    }
> > +
> > +    return true;
> > +}
> > +
> >  static void vhost_dev_sync_region(struct vhost_dev *dev,
> >                                    MemoryRegionSection *section,
> >                                    uint64_t mfirst, uint64_t mlast,
> > @@ -457,6 +469,7 @@ static void vhost_set_memory(MemoryListener *listener,
> >      dev->mem_changed_start_addr = MIN(dev->mem_changed_start_addr, 
> > start_addr);
> >      dev->mem_changed_end_addr = MAX(dev->mem_changed_end_addr, start_addr 
> > + size - 1);
> >      dev->memory_changed = true;
> > +    used_memslots = dev->mem->nregions;
> >  }
> >  
> >  static bool vhost_section(MemoryRegionSection *section)
> > @@ -1119,6 +1132,14 @@ int vhost_dev_start(struct vhost_dev *hdev, 
> > VirtIODevice *vdev)
> >      if (r < 0) {
> >          goto fail_features;
> >      }
> > +
> > +    r = hdev->vhost_ops->vhost_backend_memslots_limit(hdev);
> > +    if (memslots_limit > 0) {
> > +        memslots_limit = MIN(memslots_limit, r);
> > +    } else {
> > +        memslots_limit = r;
> > +    }
> > +
> >      r = hdev->vhost_ops->vhost_call(hdev, VHOST_SET_MEM_TABLE, hdev->mem);
> >      if (r < 0) {
> >          r = -errno;
> > diff --git a/include/hw/virtio/vhost-backend.h 
> > b/include/hw/virtio/vhost-backend.h
> > index e472f29..28b6714 100644
> > --- a/include/hw/virtio/vhost-backend.h
> > +++ b/include/hw/virtio/vhost-backend.h
> > @@ -24,12 +24,14 @@ typedef int (*vhost_call)(struct vhost_dev *dev, 
> > unsigned long int request,
> >               void *arg);
> >  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 struct VhostOps {
> >      VhostBackendType backend_type;
> >      vhost_call vhost_call;
> >      vhost_backend_init vhost_backend_init;
> >      vhost_backend_cleanup vhost_backend_cleanup;
> > +    vhost_backend_memslots_limit vhost_backend_memslots_limit;
> >  } VhostOps;
> >  
> >  extern const VhostOps user_ops;
> > diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> > index dd51050..17ff7b6 100644
> > --- a/include/hw/virtio/vhost.h
> > +++ b/include/hw/virtio/vhost.h
> > @@ -81,4 +81,5 @@ uint64_t vhost_get_features(struct vhost_dev *hdev, const 
> > int *feature_bits,
> >                              uint64_t features);
> >  void vhost_ack_features(struct vhost_dev *hdev, const int *feature_bits,
> >                          uint64_t features);
> > +bool vhost_has_free_slot(void);
> >  #endif
> > diff --git a/stubs/Makefile.objs b/stubs/Makefile.objs
> > index 9937a12..d2f1b21 100644
> > --- a/stubs/Makefile.objs
> > +++ b/stubs/Makefile.objs
> > @@ -38,3 +38,4 @@ stub-obj-$(CONFIG_WIN32) += fd-register.o
> >  stub-obj-y += cpus.o
> >  stub-obj-y += kvm.o
> >  stub-obj-y += qmp_pc_dimm_device_list.o
> > +stub-obj-y += vhost.o
> > diff --git a/stubs/vhost.c b/stubs/vhost.c
> > new file mode 100644
> > index 0000000..d346b85
> > --- /dev/null
> > +++ b/stubs/vhost.c
> > @@ -0,0 +1,6 @@
> > +#include "hw/virtio/vhost.h"
> > +
> > +bool vhost_has_free_slot(void)
> > +{
> > +    return true;
> > +}
> > -- 
> > 1.8.3.1
>