Commit 856d7245 authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

memory: add reference counting to FlatView 



With this change, a FlatView can be used even after a concurrent
update has replaced it.  Because we do not yet have RCU, we use a
mutex to protect the small critical sections that read/write the
as->current_map pointer.  Accesses to the FlatView can be done
outside the mutex.

If a MemoryRegion will be used after the FlatView is unref-ed (or after
a MemoryListener callback is returned), a reference has to be added to
that MemoryRegion. memory_region_find already does it for the region
that it returns.  The same will be done for address_space_translate
as soon as the dispatch tree is also converted to RCU-style.

Reviewed-by: default avatarAnthony Liguori <aliguori@us.ibm.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent a9a0c06d

memory.c

+69 −10
Original line number Diff line number Diff line
@@ -29,12 +29,26 @@ static unsigned memory_region_transaction_depth; 
static bool memory_region_update_pending;

static bool global_dirty_log = false;



/* flat_view_mutex is taken around reading as->current_map; the critical

 * section is extremely short, so I'm using a single mutex for every AS.

 * We could also RCU for the read-side.

 *

 * The BQL is taken around transaction commits, hence both locks are taken

 * while writing to as->current_map (with the BQL taken outside).

 */

static QemuMutex flat_view_mutex;



static QTAILQ_HEAD(memory_listeners, MemoryListener) memory_listeners

    = QTAILQ_HEAD_INITIALIZER(memory_listeners);



static QTAILQ_HEAD(, AddressSpace) address_spaces

    = QTAILQ_HEAD_INITIALIZER(address_spaces);



static void memory_init(void)

{

    qemu_mutex_init(&flat_view_mutex);

}



typedef struct AddrRange AddrRange;



/*
@@ -225,6 +239,7 @@ struct FlatRange { 
 * order.

 */

struct FlatView {

    unsigned ref;

    FlatRange *ranges;

    unsigned nr;

    unsigned nr_allocated;
@@ -246,6 +261,7 @@ static bool flatrange_equal(FlatRange *a, FlatRange *b) 


static void flatview_init(FlatView *view)

{

    view->ref = 1;

    view->ranges = NULL;

    view->nr = 0;

    view->nr_allocated = 0;
@@ -279,6 +295,18 @@ static void flatview_destroy(FlatView *view) 
    g_free(view);

}



static void flatview_ref(FlatView *view)

{

    atomic_inc(&view->ref);

}



static void flatview_unref(FlatView *view)

{

    if (atomic_fetch_dec(&view->ref) == 1) {

        flatview_destroy(view);

    }

}



static bool can_merge(FlatRange *r1, FlatRange *r2)

{

    return int128_eq(addrrange_end(r1->addr), r2->addr.start)
@@ -578,6 +606,17 @@ static void address_space_add_del_ioeventfds(AddressSpace *as, 
    }

}



static FlatView *address_space_get_flatview(AddressSpace *as)

{

    FlatView *view;



    qemu_mutex_lock(&flat_view_mutex);

    view = as->current_map;

    flatview_ref(view);

    qemu_mutex_unlock(&flat_view_mutex);

    return view;

}



static void address_space_update_ioeventfds(AddressSpace *as)

{

    FlatView *view;
@@ -587,7 +626,7 @@ static void address_space_update_ioeventfds(AddressSpace *as) 
    AddrRange tmp;

    unsigned i;



    view = as->current_map;

    view = address_space_get_flatview(as);

    FOR_EACH_FLAT_RANGE(fr, view) {

        for (i = 0; i < fr->mr->ioeventfd_nb; ++i) {

            tmp = addrrange_shift(fr->mr->ioeventfds[i].addr,
@@ -609,6 +648,7 @@ static void address_space_update_ioeventfds(AddressSpace *as) 
    g_free(as->ioeventfds);

    as->ioeventfds = ioeventfds;

    as->ioeventfd_nb = ioeventfd_nb;

    flatview_unref(view);

}



static void address_space_update_topology_pass(AddressSpace *as,
@@ -676,14 +716,25 @@ static void address_space_update_topology_pass(AddressSpace *as, 


static void address_space_update_topology(AddressSpace *as)

{

    FlatView *old_view = as->current_map;

    FlatView *old_view = address_space_get_flatview(as);

    FlatView *new_view = generate_memory_topology(as->root);



    address_space_update_topology_pass(as, old_view, new_view, false);

    address_space_update_topology_pass(as, old_view, new_view, true);



    qemu_mutex_lock(&flat_view_mutex);

    flatview_unref(as->current_map);

    as->current_map = new_view;

    flatview_destroy(old_view);

    qemu_mutex_unlock(&flat_view_mutex);



    /* Note that all the old MemoryRegions are still alive up to this

     * point.  This relieves most MemoryListeners from the need to

     * ref/unref the MemoryRegions they get---unless they use them

     * outside the iothread mutex, in which case precise reference

     * counting is necessary.

     */

    flatview_unref(old_view);



    address_space_update_ioeventfds(as);

}
@@ -1148,12 +1199,13 @@ void memory_region_sync_dirty_bitmap(MemoryRegion *mr) 
    FlatRange *fr;



    QTAILQ_FOREACH(as, &address_spaces, address_spaces_link) {

        FlatView *view = as->current_map;

        FlatView *view = address_space_get_flatview(as);

        FOR_EACH_FLAT_RANGE(fr, view) {

            if (fr->mr == mr) {

                MEMORY_LISTENER_UPDATE_REGION(fr, as, Forward, log_sync);

            }

        }

        flatview_unref(view);

    }

}
@@ -1205,7 +1257,7 @@ static void memory_region_update_coalesced_range_as(MemoryRegion *mr, AddressSpa 
    AddrRange tmp;

    MemoryRegionSection section;



    view = as->current_map;

    view = address_space_get_flatview(as);

    FOR_EACH_FLAT_RANGE(fr, view) {

        if (fr->mr == mr) {

            section = (MemoryRegionSection) {
@@ -1231,6 +1283,7 @@ static void memory_region_update_coalesced_range_as(MemoryRegion *mr, AddressSpa 
            }

        }

    }

    flatview_unref(view);

}



static void memory_region_update_coalesced_range(MemoryRegion *mr)
@@ -1532,7 +1585,7 @@ MemoryRegionSection memory_region_find(MemoryRegion *mr, 
    as = memory_region_to_address_space(root);

    range = addrrange_make(int128_make64(addr), int128_make64(size));



    view = as->current_map;

    view = address_space_get_flatview(as);

    fr = flatview_lookup(view, range);

    if (!fr) {

        return ret;
@@ -1553,6 +1606,7 @@ MemoryRegionSection memory_region_find(MemoryRegion *mr, 
    ret.readonly = fr->readonly;

    memory_region_ref(ret.mr);



    flatview_unref(view);

    return ret;

}
@@ -1561,10 +1615,11 @@ void address_space_sync_dirty_bitmap(AddressSpace *as) 
    FlatView *view;

    FlatRange *fr;



    view = as->current_map;

    view = address_space_get_flatview(as);

    FOR_EACH_FLAT_RANGE(fr, view) {

        MEMORY_LISTENER_UPDATE_REGION(fr, as, Forward, log_sync);

    }

    flatview_unref(view);

}



void memory_global_dirty_log_start(void)
@@ -1596,7 +1651,7 @@ static void listener_add_address_space(MemoryListener *listener, 
        }

    }



    view = as->current_map;

    view = address_space_get_flatview(as);

    FOR_EACH_FLAT_RANGE(fr, view) {

        MemoryRegionSection section = {

            .mr = fr->mr,
@@ -1610,6 +1665,7 @@ static void listener_add_address_space(MemoryListener *listener, 
            listener->region_add(listener, &section);

        }

    }

    flatview_unref(view);

}



void memory_listener_register(MemoryListener *listener, AddressSpace *filter)
@@ -1643,6 +1699,10 @@ void memory_listener_unregister(MemoryListener *listener) 


void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name)

{

    if (QTAILQ_EMPTY(&address_spaces)) {

        memory_init();

    }



    memory_region_transaction_begin();

    as->root = root;

    as->current_map = g_new(FlatView, 1);
@@ -1664,9 +1724,8 @@ void address_space_destroy(AddressSpace *as) 
    memory_region_transaction_commit();

    QTAILQ_REMOVE(&address_spaces, as, address_spaces_link);

    address_space_destroy_dispatch(as);

    flatview_destroy(as->current_map);

    flatview_unref(as->current_map);

    g_free(as->name);

    g_free(as->current_map);

    g_free(as->ioeventfds);

}