Re: [Qemu-devel] [PATCH v6 1/3] memory: introduce IOMMUNotifier and its caps

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Sep 21, 2016 at 12:58:54PM +0800, Peter Xu wrote:
> IOMMU Notifier list is used for notifying IO address mapping changes.
> Currently VFIO is the only user.
> 
> However it is possible that future consumer like vhost would like to
> only listen to part of its notifications (e.g., cache invalidations).
> 
> This patch introduced IOMMUNotifier and IOMMUNotfierFlag bits for a
> finer grained control of it.
> 
> IOMMUNotifier contains a bitfield for the notify consumer describing
> what kind of notification it is interested in. Currently two kinds of
> notifications are defined:
> 
> - IOMMU_NOTIFIER_MAP:    for newly mapped entries (additions)
> - IOMMU_NOTIFIER_UNMAP:  for entries to be removed (cache invalidates)
> 
> When registering the IOMMU notifier, we need to specify one or multiple
> types of messages to listen to.
> 
> When notifications are triggered, its type will be checked against the
> notifier's type bits, and only notifiers with registered bits will be
> notified.
> 
> (For any IOMMU implementation, an in-place mapping change should be
>  notified with an UNMAP followed by a MAP.)

Ok, I wasn't clear.  I meant a big fat comment in the *code*, not just
in the commit message.  It should not be necessary to look at the
commit history to figure out how to use an interface correctly

Even a comment in the code is barely adequate, compared to designing
the interface signatures such that it's obvious.

Please bear in mind:
    http://ozlabs.org/~rusty/index.cgi/tech/2008-03-30.html
and http://ozlabs.org/~rusty/index.cgi/tech/2008-04-01.html


Couple of other tiny nits that I wouldn't bother with it weren't for
the above.

> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  hw/vfio/common.c              |  3 ++-
>  include/exec/memory.h         | 38 +++++++++++++++++++++++++++++++-------
>  include/hw/vfio/vfio-common.h |  2 +-
>  memory.c                      | 37 ++++++++++++++++++++++++++++---------
>  4 files changed, 62 insertions(+), 18 deletions(-)
> 
> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
> index b313e7c..89a993b 100644
> --- a/hw/vfio/common.c
> +++ b/hw/vfio/common.c
> @@ -293,7 +293,7 @@ static bool vfio_listener_skipped_section(MemoryRegionSection *section)
>             section->offset_within_address_space & (1ULL << 63);
>  }
>  
> -static void vfio_iommu_map_notify(Notifier *n, void *data)
> +static void vfio_iommu_map_notify(IOMMUNotifier *n, IOMMUTLBEntry *data)

This change leaves a now pointless IOMMUTLBEntry *iotlb = data a few
lines below.

>  {
>      VFIOGuestIOMMU *giommu = container_of(n, VFIOGuestIOMMU, n);
>      VFIOContainer *container = giommu->container;
> @@ -454,6 +454,7 @@ static void vfio_listener_region_add(MemoryListener *listener,
>                                 section->offset_within_region;
>          giommu->container = container;
>          giommu->n.notify = vfio_iommu_map_notify;
> +        giommu->n.notifier_flags = IOMMU_NOTIFIER_ALL;
>          QLIST_INSERT_HEAD(&container->giommu_list, giommu, giommu_next);
>  
>          memory_region_register_iommu_notifier(giommu->iommu, &giommu->n);
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 3e4d416..a3ec7aa 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -67,6 +67,27 @@ struct IOMMUTLBEntry {
>      IOMMUAccessFlags perm;
>  };
>  
> +/*
> + * Bitmap for differnet IOMMUNotifier capabilities. Each notifier can

s/differnet/different/

> + * register with one or multiple IOMMU Notifier capability bit(s).
> + */
> +typedef enum {
> +    IOMMU_NOTIFIER_NONE = 0,
> +    /* Notify cache invalidations */
> +    IOMMU_NOTIFIER_UNMAP = 0x1,
> +    /* Notify entry changes (newly created entries) */
> +    IOMMU_NOTIFIER_MAP = 0x2,
> +} IOMMUNotifierFlag;
> +
> +#define IOMMU_NOTIFIER_ALL (IOMMU_NOTIFIER_MAP | IOMMU_NOTIFIER_UNMAP)
> +
> +struct IOMMUNotifier {
> +    void (*notify)(struct IOMMUNotifier *notifier, IOMMUTLBEntry *data);
> +    IOMMUNotifierFlag notifier_flags;
> +    QLIST_ENTRY(IOMMUNotifier) node;
> +};
> +typedef struct IOMMUNotifier IOMMUNotifier;
> +
>  /* New-style MMIO accessors can indicate that the transaction failed.
>   * A zero (MEMTX_OK) response means success; anything else is a failure
>   * of some kind. The memory subsystem will bitwise-OR together results
> @@ -201,7 +222,7 @@ struct MemoryRegion {
>      const char *name;
>      unsigned ioeventfd_nb;
>      MemoryRegionIoeventfd *ioeventfds;
> -    NotifierList iommu_notify;
> +    QLIST_HEAD(, IOMMUNotifier) iommu_notify;
>  };
>  
>  /**
> @@ -620,11 +641,12 @@ void memory_region_notify_iommu(MemoryRegion *mr,
>   * IOMMU translation entries.
>   *
>   * @mr: the memory region to observe
> - * @n: the notifier to be added; the notifier receives a pointer to an
> - *     #IOMMUTLBEntry as the opaque value; the pointer ceases to be
> - *     valid on exit from the notifier.
> + * @n: the IOMMUNotifier to be added; the notify callback receives a
> + *     pointer to an #IOMMUTLBEntry as the opaque value; the pointer
> + *     ceases to be valid on exit from the notifier.
>   */
> -void memory_region_register_iommu_notifier(MemoryRegion *mr, Notifier *n);
> +void memory_region_register_iommu_notifier(MemoryRegion *mr,
> +                                           IOMMUNotifier *n);
>  
>  /**
>   * memory_region_iommu_replay: replay existing IOMMU translations to
> @@ -636,7 +658,8 @@ void memory_region_register_iommu_notifier(MemoryRegion *mr, Notifier *n);
>   * @is_write: Whether to treat the replay as a translate "write"
>   *     through the iommu
>   */
> -void memory_region_iommu_replay(MemoryRegion *mr, Notifier *n, bool is_write);
> +void memory_region_iommu_replay(MemoryRegion *mr, IOMMUNotifier *n,
> +                                bool is_write);
>  
>  /**
>   * memory_region_unregister_iommu_notifier: unregister a notifier for
> @@ -646,7 +669,8 @@ void memory_region_iommu_replay(MemoryRegion *mr, Notifier *n, bool is_write);
>   *      needs to be called
>   * @n: the notifier to be removed.
>   */
> -void memory_region_unregister_iommu_notifier(MemoryRegion *mr, Notifier *n);
> +void memory_region_unregister_iommu_notifier(MemoryRegion *mr,
> +                                             IOMMUNotifier *n);
>  
>  /**
>   * memory_region_name: get a memory region's name
> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
> index 94dfae3..c17602e 100644
> --- a/include/hw/vfio/vfio-common.h
> +++ b/include/hw/vfio/vfio-common.h
> @@ -93,7 +93,7 @@ typedef struct VFIOGuestIOMMU {
>      VFIOContainer *container;
>      MemoryRegion *iommu;
>      hwaddr iommu_offset;
> -    Notifier n;
> +    IOMMUNotifier n;
>      QLIST_ENTRY(VFIOGuestIOMMU) giommu_next;
>  } VFIOGuestIOMMU;
>  
> diff --git a/memory.c b/memory.c
> index 1a1baf5..69d9d9a 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -1413,7 +1413,7 @@ void memory_region_init_iommu(MemoryRegion *mr,
>      memory_region_init(mr, owner, name, size);
>      mr->iommu_ops = ops,
>      mr->terminates = true;  /* then re-forwards */
> -    notifier_list_init(&mr->iommu_notify);
> +    QLIST_INIT(&mr->iommu_notify);
>  }
>  
>  static void memory_region_finalize(Object *obj)
> @@ -1508,13 +1508,16 @@ bool memory_region_is_logging(MemoryRegion *mr, uint8_t client)
>      return memory_region_get_dirty_log_mask(mr) & (1 << client);
>  }
>  
> -void memory_region_register_iommu_notifier(MemoryRegion *mr, Notifier *n)
> +void memory_region_register_iommu_notifier(MemoryRegion *mr,
> +                                           IOMMUNotifier *n)
>  {
> +    /* We need to register for at least one bitfield */
> +    assert(n->notifier_flags != IOMMU_NOTIFIER_NONE);
>      if (mr->iommu_ops->notify_started &&
> -        QLIST_EMPTY(&mr->iommu_notify.notifiers)) {
> +        QLIST_EMPTY(&mr->iommu_notify)) {
>          mr->iommu_ops->notify_started(mr);
>      }
> -    notifier_list_add(&mr->iommu_notify, n);
> +    QLIST_INSERT_HEAD(&mr->iommu_notify, n, node);
>  }
>  
>  uint64_t memory_region_iommu_get_min_page_size(MemoryRegion *mr)
> @@ -1526,7 +1529,8 @@ uint64_t memory_region_iommu_get_min_page_size(MemoryRegion *mr)
>      return TARGET_PAGE_SIZE;
>  }
>  
> -void memory_region_iommu_replay(MemoryRegion *mr, Notifier *n, bool is_write)
> +void memory_region_iommu_replay(MemoryRegion *mr, IOMMUNotifier *n,
> +                                bool is_write)
>  {
>      hwaddr addr, granularity;
>      IOMMUTLBEntry iotlb;
> @@ -1547,11 +1551,12 @@ void memory_region_iommu_replay(MemoryRegion *mr, Notifier *n, bool is_write)
>      }
>  }
>  
> -void memory_region_unregister_iommu_notifier(MemoryRegion *mr, Notifier *n)
> +void memory_region_unregister_iommu_notifier(MemoryRegion *mr,
> +                                             IOMMUNotifier *n)
>  {
> -    notifier_remove(n);
> +    QLIST_REMOVE(n, node);
>      if (mr->iommu_ops->notify_stopped &&
> -        QLIST_EMPTY(&mr->iommu_notify.notifiers)) {
> +        QLIST_EMPTY(&mr->iommu_notify)) {
>          mr->iommu_ops->notify_stopped(mr);
>      }
>  }
> @@ -1559,8 +1564,22 @@ void memory_region_unregister_iommu_notifier(MemoryRegion *mr, Notifier *n)
>  void memory_region_notify_iommu(MemoryRegion *mr,
>                                  IOMMUTLBEntry entry)
>  {
> +    IOMMUNotifier *iommu_notifier;
> +    IOMMUNotifierFlag request_flags;
> +
>      assert(memory_region_is_iommu(mr));
> -    notifier_list_notify(&mr->iommu_notify, &entry);
> +
> +    if (entry.perm & IOMMU_RW) {
> +        request_flags = IOMMU_NOTIFIER_MAP;
> +    } else {
> +        request_flags = IOMMU_NOTIFIER_UNMAP;
> +    }
> +
> +    QLIST_FOREACH(iommu_notifier, &mr->iommu_notify, node) {
> +        if (iommu_notifier->notifier_flags & request_flags) {
> +            iommu_notifier->notify(iommu_notifier, &entry);
> +        }
> +    }
>  }
>  
>  void memory_region_set_log(MemoryRegion *mr, bool log, unsigned client)

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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