[PATCH v10 0/7] Support message-based DMA in vfio-user server

[PATCH v10 0/7] Support message-based DMA in vfio-user server

[Mattias Nissler]

This series adds basic support for message-based DMA in qemu's vfio-user
server. This is useful for cases where the client does not provide file
descriptors for accessing system memory via memory mappings. My motivating use
case is to hook up device models as PCIe endpoints to a hardware design. This
works by bridging the PCIe transaction layer to vfio-user, and the endpoint
does not access memory directly, but sends memory requests TLPs to the hardware
design in order to perform DMA.

Note that more work is needed to make message-based DMA work well: qemu
currently breaks down DMA accesses into chunks of size 8 bytes at maximum, each
of which will be handled in a separate vfio-user DMA request message. This is
quite terrible for large DMA accesses, such as when nvme reads and writes
page-sized blocks for example. Thus, I would like to improve qemu to be able to
perform larger accesses, at least for indirect memory regions. I have something
working locally, but since this will likely result in more involved surgery and
discussion, I am leaving this to be addressed in a separate patch.

Changes from v1:

* Address Stefan's review comments. In particular, enforce an allocation limit
  and don't drop the map client callbacks given that map requests can fail when
  hitting size limits.

* libvfio-user version bump now included in the series.

* Tested as well on big-endian s390x. This uncovered another byte order issue
  in vfio-user server code that I've included a fix for.

Changes from v2:

* Add a preparatory patch to make bounce buffering an AddressSpace-specific
  concept.

* The total buffer size limit parameter is now per AdressSpace and can be
  configured for PCIDevice via a property.

* Store a magic value in first bytes of bounce buffer struct as a best effort
  measure to detect invalid pointers in address_space_unmap.

Changes from v3:

* libvfio-user now supports twin-socket mode which uses separate sockets for
  client->server and server->client commands, respectively. This addresses the
  concurrent command bug triggered by server->client DMA access commands. See
  https://github.com/nutanix/libvfio-user/issues/279 for details.

* Add missing teardown code in do_address_space_destroy.

* Fix bounce buffer size bookkeeping race condition.

* Generate unmap notification callbacks unconditionally.

* Some cosmetic fixes.

Changes from v4:

* Fix accidentally dropped memory_region_unref, control flow restored to match
  previous code to simplify review.

* Some cosmetic fixes.

Changes from v5:

* Unregister indirect memory region in libvfio-user dma_unregister callback.

Changes from v6:

* Rebase, resolve straightforward merge conflict in system/dma-helpers.c

Changes from v7:

* Rebase (applied cleanly)

* Restore various Reviewed-by and Tested-by tags that I failed to carry
  forward (I double-checked that the patches haven't changed since the reviewed
  version)

Changes from v8:

* Rebase (clean)

* Change bounce buffer size accounting to use uint32_t so it works also on
  hosts that don't support uint64_t atomics, such as mipsel. As a consequence
  overflows are a real concern now, so switch to a cmpxchg loop for allocating
  bounce buffer space.

Changes from v9:

* Incorporate patch split and QEMU_MUTEX_GUARD change by philmd@linaro.org

* Use size_t instead of uint32_t for bounce buffer size accounting. The qdev
  property remains uint32_t though, so it has a consistent size regardless of
  host.

Mattias Nissler (6):
  system/physmem: Propagate AddressSpace to MapClient helpers
  system/physmem: Per-AddressSpace bounce buffering
  softmmu: Support concurrent bounce buffers
  Update subprojects/libvfio-user
  vfio-user: Message-based DMA support
  vfio-user: Fix config space access byte order

Philippe Mathieu-Daudé (1):
  system/physmem: Replace qemu_mutex_lock() calls with QEMU_LOCK_GUARD

 hw/pci/pci.c                  |   8 ++
 hw/remote/trace-events        |   2 +
 hw/remote/vfio-user-obj.c     | 104 ++++++++++++++++++++-----
 include/exec/cpu-common.h     |   2 -
 include/exec/memory.h         |  41 +++++++++-
 include/hw/pci/pci_device.h   |   3 +
 subprojects/libvfio-user.wrap |   2 +-
 system/dma-helpers.c          |   4 +-
 system/memory.c               |   8 ++
 system/physmem.c              | 140 ++++++++++++++++++----------------
 10 files changed, 225 insertions(+), 89 deletions(-)

-- 
2.43.2

[PATCH v10 1/7] system/physmem: Replace qemu_mutex_lock() calls with QEMU_LOCK_GUARD

[Mattias Nissler]

From: Philippe Mathieu-Daudé <philmd@linaro.org>

From: Philippe Mathieu-Daudé <philmd@linaro.org>

Simplify cpu_[un]register_map_client() and cpu_notify_map_clients()
by replacing the pair of qemu_mutex_lock/qemu_mutex_unlock calls by
the WITH_QEMU_LOCK_GUARD() macro.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Mattias Nissler <mnissler@rivosinc.com>
Reviewed-by: Mattias Nissler <mnissler@rivosinc.com>
---
 system/physmem.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/system/physmem.c b/system/physmem.c
index d3a3d8a45c..5486014cf2 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -3086,7 +3086,7 @@ void cpu_register_map_client(QEMUBH *bh)
 {
     MapClient *client = g_malloc(sizeof(*client));
 
-    qemu_mutex_lock(&map_client_list_lock);
+    QEMU_LOCK_GUARD(&map_client_list_lock);
     client->bh = bh;
     QLIST_INSERT_HEAD(&map_client_list, client, link);
     /* Write map_client_list before reading in_use.  */
@@ -3094,7 +3094,6 @@ void cpu_register_map_client(QEMUBH *bh)
     if (!qatomic_read(&bounce.in_use)) {
         cpu_notify_map_clients_locked();
     }
-    qemu_mutex_unlock(&map_client_list_lock);
 }
 
 void cpu_exec_init_all(void)
@@ -3117,21 +3116,19 @@ void cpu_unregister_map_client(QEMUBH *bh)
 {
     MapClient *client;
 
-    qemu_mutex_lock(&map_client_list_lock);
+    QEMU_LOCK_GUARD(&map_client_list_lock);
     QLIST_FOREACH(client, &map_client_list, link) {
         if (client->bh == bh) {
             cpu_unregister_map_client_do(client);
             break;
         }
     }
-    qemu_mutex_unlock(&map_client_list_lock);
 }
 
 static void cpu_notify_map_clients(void)
 {
-    qemu_mutex_lock(&map_client_list_lock);
+    QEMU_LOCK_GUARD(&map_client_list_lock);
     cpu_notify_map_clients_locked();
-    qemu_mutex_unlock(&map_client_list_lock);
 }
 
 static bool flatview_access_valid(FlatView *fv, hwaddr addr, hwaddr len,
-- 
2.43.2

[PATCH v10 2/7] system/physmem: Propagate AddressSpace to MapClient helpers

[Mattias Nissler]

Propagate AddressSpace handler to following helpers:
- register_map_client()
- unregister_map_client()
- notify_map_clients[_locked]()

Rename them using 'address_space_' prefix instead of 'cpu_'.

The AddressSpace argument will be used in the next commit.

Reviewed-by: Peter Xu <peterx@redhat.com>
Tested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Mattias Nissler <mnissler@rivosinc.com>
Message-ID: <20240507094210.300566-2-mnissler@rivosinc.com>
[PMD: Split patch, part 1/2]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Mattias Nissler <mnissler@rivosinc.com>
---
 include/exec/cpu-common.h |  2 --
 include/exec/memory.h     | 26 ++++++++++++++++++++++++--
 system/dma-helpers.c      |  4 ++--
 system/physmem.c          | 24 ++++++++++++------------
 4 files changed, 38 insertions(+), 18 deletions(-)

diff --git a/include/exec/cpu-common.h b/include/exec/cpu-common.h
index 8bc397e251..815342d043 100644
--- a/include/exec/cpu-common.h
+++ b/include/exec/cpu-common.h
@@ -147,8 +147,6 @@ void *cpu_physical_memory_map(hwaddr addr,
                               bool is_write);
 void cpu_physical_memory_unmap(void *buffer, hwaddr len,
                                bool is_write, hwaddr access_len);
-void cpu_register_map_client(QEMUBH *bh);
-void cpu_unregister_map_client(QEMUBH *bh);
 
 bool cpu_physical_memory_is_io(hwaddr phys_addr);
 
diff --git a/include/exec/memory.h b/include/exec/memory.h
index dadb5cd65a..e1e0c5a3de 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -2946,8 +2946,8 @@ bool address_space_access_valid(AddressSpace *as, hwaddr addr, hwaddr len,
  * May return %NULL and set *@plen to zero(0), if resources needed to perform
  * the mapping are exhausted.
  * Use only for reads OR writes - not for read-modify-write operations.
- * Use cpu_register_map_client() to know when retrying the map operation is
- * likely to succeed.
+ * Use address_space_register_map_client() to know when retrying the map
+ * operation is likely to succeed.
  *
  * @as: #AddressSpace to be accessed
  * @addr: address within that address space
@@ -2972,6 +2972,28 @@ void *address_space_map(AddressSpace *as, hwaddr addr,
 void address_space_unmap(AddressSpace *as, void *buffer, hwaddr len,
                          bool is_write, hwaddr access_len);
 
+/*
+ * address_space_register_map_client: Register a callback to invoke when
+ * resources for address_space_map() are available again.
+ *
+ * address_space_map may fail when there are not enough resources available,
+ * such as when bounce buffer memory would exceed the limit. The callback can
+ * be used to retry the address_space_map operation. Note that the callback
+ * gets automatically removed after firing.
+ *
+ * @as: #AddressSpace to be accessed
+ * @bh: callback to invoke when address_space_map() retry is appropriate
+ */
+void address_space_register_map_client(AddressSpace *as, QEMUBH *bh);
+
+/*
+ * address_space_unregister_map_client: Unregister a callback that has
+ * previously been registered and not fired yet.
+ *
+ * @as: #AddressSpace to be accessed
+ * @bh: callback to unregister
+ */
+void address_space_unregister_map_client(AddressSpace *as, QEMUBH *bh);
 
 /* Internal functions, part of the implementation of address_space_read.  */
 MemTxResult address_space_read_full(AddressSpace *as, hwaddr addr,
diff --git a/system/dma-helpers.c b/system/dma-helpers.c
index 9b221cf94e..74013308f5 100644
--- a/system/dma-helpers.c
+++ b/system/dma-helpers.c
@@ -169,7 +169,7 @@ static void dma_blk_cb(void *opaque, int ret)
     if (dbs->iov.size == 0) {
         trace_dma_map_wait(dbs);
         dbs->bh = aio_bh_new(ctx, reschedule_dma, dbs);
-        cpu_register_map_client(dbs->bh);
+        address_space_register_map_client(dbs->sg->as, dbs->bh);
         return;
     }
 
@@ -197,7 +197,7 @@ static void dma_aio_cancel(BlockAIOCB *acb)
     }
 
     if (dbs->bh) {
-        cpu_unregister_map_client(dbs->bh);
+        address_space_unregister_map_client(dbs->sg->as, dbs->bh);
         qemu_bh_delete(dbs->bh);
         dbs->bh = NULL;
     }
diff --git a/system/physmem.c b/system/physmem.c
index 5486014cf2..27e754ff57 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -3065,24 +3065,24 @@ QemuMutex map_client_list_lock;
 static QLIST_HEAD(, MapClient) map_client_list
     = QLIST_HEAD_INITIALIZER(map_client_list);
 
-static void cpu_unregister_map_client_do(MapClient *client)
+static void address_space_unregister_map_client_do(MapClient *client)
 {
     QLIST_REMOVE(client, link);
     g_free(client);
 }
 
-static void cpu_notify_map_clients_locked(void)
+static void address_space_notify_map_clients_locked(AddressSpace *as)
 {
     MapClient *client;
 
     while (!QLIST_EMPTY(&map_client_list)) {
         client = QLIST_FIRST(&map_client_list);
         qemu_bh_schedule(client->bh);
-        cpu_unregister_map_client_do(client);
+        address_space_unregister_map_client_do(client);
     }
 }
 
-void cpu_register_map_client(QEMUBH *bh)
+void address_space_register_map_client(AddressSpace *as, QEMUBH *bh)
 {
     MapClient *client = g_malloc(sizeof(*client));
 
@@ -3092,7 +3092,7 @@ void cpu_register_map_client(QEMUBH *bh)
     /* Write map_client_list before reading in_use.  */
     smp_mb();
     if (!qatomic_read(&bounce.in_use)) {
-        cpu_notify_map_clients_locked();
+        address_space_notify_map_clients_locked(as);
     }
 }
 
@@ -3112,23 +3112,23 @@ void cpu_exec_init_all(void)
     qemu_mutex_init(&map_client_list_lock);
 }
 
-void cpu_unregister_map_client(QEMUBH *bh)
+void address_space_unregister_map_client(AddressSpace *as, QEMUBH *bh)
 {
     MapClient *client;
 
     QEMU_LOCK_GUARD(&map_client_list_lock);
     QLIST_FOREACH(client, &map_client_list, link) {
         if (client->bh == bh) {
-            cpu_unregister_map_client_do(client);
+            address_space_unregister_map_client_do(client);
             break;
         }
     }
 }
 
-static void cpu_notify_map_clients(void)
+static void address_space_notify_map_clients(AddressSpace *as)
 {
     QEMU_LOCK_GUARD(&map_client_list_lock);
-    cpu_notify_map_clients_locked();
+    address_space_notify_map_clients_locked(as);
 }
 
 static bool flatview_access_valid(FlatView *fv, hwaddr addr, hwaddr len,
@@ -3195,8 +3195,8 @@ flatview_extend_translation(FlatView *fv, hwaddr addr,
  * May map a subset of the requested range, given by and returned in *plen.
  * May return NULL if resources needed to perform the mapping are exhausted.
  * Use only for reads OR writes - not for read-modify-write operations.
- * Use cpu_register_map_client() to know when retrying the map operation is
- * likely to succeed.
+ * Use address_space_register_map_client() to know when retrying the map
+ * operation is likely to succeed.
  */
 void *address_space_map(AddressSpace *as,
                         hwaddr addr,
@@ -3279,7 +3279,7 @@ void address_space_unmap(AddressSpace *as, void *buffer, hwaddr len,
     memory_region_unref(bounce.mr);
     /* Clear in_use before reading map_client_list.  */
     qatomic_set_mb(&bounce.in_use, false);
-    cpu_notify_map_clients();
+    address_space_notify_map_clients(as);
 }
 
 void *cpu_physical_memory_map(hwaddr addr,
-- 
2.43.2

[PATCH v10 3/7] system/physmem: Per-AddressSpace bounce buffering

[Mattias Nissler]

Instead of using a single global bounce buffer, give each AddressSpace
its own bounce buffer. The MapClient callback mechanism moves to
AddressSpace accordingly.

This is in preparation for generalizing bounce buffer handling further
to allow multiple bounce buffers, with a total allocation limit
configured per AddressSpace.

Reviewed-by: Peter Xu <peterx@redhat.com>
Tested-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Mattias Nissler <mnissler@rivosinc.com>
Message-ID: <20240507094210.300566-2-mnissler@rivosinc.com>
[PMD: Split patch, part 2/2]
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Mattias Nissler <mnissler@rivosinc.com>
---
 include/exec/memory.h | 19 +++++++++++
 system/memory.c       |  7 +++++
 system/physmem.c      | 73 ++++++++++++++++---------------------------
 3 files changed, 53 insertions(+), 46 deletions(-)

diff --git a/include/exec/memory.h b/include/exec/memory.h
index e1e0c5a3de..d417d7f363 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -1112,6 +1112,19 @@ struct MemoryListener {
     QTAILQ_ENTRY(MemoryListener) link_as;
 };
 
+typedef struct AddressSpaceMapClient {
+    QEMUBH *bh;
+    QLIST_ENTRY(AddressSpaceMapClient) link;
+} AddressSpaceMapClient;
+
+typedef struct {
+    MemoryRegion *mr;
+    void *buffer;
+    hwaddr addr;
+    hwaddr len;
+    bool in_use;
+} BounceBuffer;
+
 /**
  * struct AddressSpace: describes a mapping of addresses to #MemoryRegion objects
  */
@@ -1129,6 +1142,12 @@ struct AddressSpace {
     struct MemoryRegionIoeventfd *ioeventfds;
     QTAILQ_HEAD(, MemoryListener) listeners;
     QTAILQ_ENTRY(AddressSpace) address_spaces_link;
+
+    /* Bounce buffer to use for this address space. */
+    BounceBuffer bounce;
+    /* List of callbacks to invoke when buffers free up */
+    QemuMutex map_client_list_lock;
+    QLIST_HEAD(, AddressSpaceMapClient) map_client_list;
 };
 
 typedef struct AddressSpaceDispatch AddressSpaceDispatch;
diff --git a/system/memory.c b/system/memory.c
index 49f1cb2c38..642a449f8c 100644
--- a/system/memory.c
+++ b/system/memory.c
@@ -3174,6 +3174,9 @@ void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name)
     as->ioeventfds = NULL;
     QTAILQ_INIT(&as->listeners);
     QTAILQ_INSERT_TAIL(&address_spaces, as, address_spaces_link);
+    as->bounce.in_use = false;
+    qemu_mutex_init(&as->map_client_list_lock);
+    QLIST_INIT(&as->map_client_list);
     as->name = g_strdup(name ? name : "anonymous");
     address_space_update_topology(as);
     address_space_update_ioeventfds(as);
@@ -3181,6 +3184,10 @@ void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name)
 
 static void do_address_space_destroy(AddressSpace *as)
 {
+    assert(!qatomic_read(&as->bounce.in_use));
+    assert(QLIST_EMPTY(&as->map_client_list));
+    qemu_mutex_destroy(&as->map_client_list_lock);
+
     assert(QTAILQ_EMPTY(&as->listeners));
 
     flatview_unref(as->current_map);
diff --git a/system/physmem.c b/system/physmem.c
index 27e754ff57..62758202cf 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -3046,26 +3046,8 @@ void cpu_flush_icache_range(hwaddr start, hwaddr len)
                                      NULL, len, FLUSH_CACHE);
 }
 
-typedef struct {
-    MemoryRegion *mr;
-    void *buffer;
-    hwaddr addr;
-    hwaddr len;
-    bool in_use;
-} BounceBuffer;
-
-static BounceBuffer bounce;
-
-typedef struct MapClient {
-    QEMUBH *bh;
-    QLIST_ENTRY(MapClient) link;
-} MapClient;
-
-QemuMutex map_client_list_lock;
-static QLIST_HEAD(, MapClient) map_client_list
-    = QLIST_HEAD_INITIALIZER(map_client_list);
-
-static void address_space_unregister_map_client_do(MapClient *client)
+static void
+address_space_unregister_map_client_do(AddressSpaceMapClient *client)
 {
     QLIST_REMOVE(client, link);
     g_free(client);
@@ -3073,10 +3055,10 @@ static void address_space_unregister_map_client_do(MapClient *client)
 
 static void address_space_notify_map_clients_locked(AddressSpace *as)
 {
-    MapClient *client;
+    AddressSpaceMapClient *client;
 
-    while (!QLIST_EMPTY(&map_client_list)) {
-        client = QLIST_FIRST(&map_client_list);
+    while (!QLIST_EMPTY(&as->map_client_list)) {
+        client = QLIST_FIRST(&as->map_client_list);
         qemu_bh_schedule(client->bh);
         address_space_unregister_map_client_do(client);
     }
@@ -3084,14 +3066,14 @@ static void address_space_notify_map_clients_locked(AddressSpace *as)
 
 void address_space_register_map_client(AddressSpace *as, QEMUBH *bh)
 {
-    MapClient *client = g_malloc(sizeof(*client));
+    AddressSpaceMapClient *client = g_malloc(sizeof(*client));
 
-    QEMU_LOCK_GUARD(&map_client_list_lock);
+    QEMU_LOCK_GUARD(&as->map_client_list_lock);
     client->bh = bh;
-    QLIST_INSERT_HEAD(&map_client_list, client, link);
+    QLIST_INSERT_HEAD(&as->map_client_list, client, link);
     /* Write map_client_list before reading in_use.  */
     smp_mb();
-    if (!qatomic_read(&bounce.in_use)) {
+    if (!qatomic_read(&as->bounce.in_use)) {
         address_space_notify_map_clients_locked(as);
     }
 }
@@ -3109,15 +3091,14 @@ void cpu_exec_init_all(void)
     finalize_target_page_bits();
     io_mem_init();
     memory_map_init();
-    qemu_mutex_init(&map_client_list_lock);
 }
 
 void address_space_unregister_map_client(AddressSpace *as, QEMUBH *bh)
 {
-    MapClient *client;
+    AddressSpaceMapClient *client;
 
-    QEMU_LOCK_GUARD(&map_client_list_lock);
-    QLIST_FOREACH(client, &map_client_list, link) {
+    QEMU_LOCK_GUARD(&as->map_client_list_lock);
+    QLIST_FOREACH(client, &as->map_client_list, link) {
         if (client->bh == bh) {
             address_space_unregister_map_client_do(client);
             break;
@@ -3127,7 +3108,7 @@ void address_space_unregister_map_client(AddressSpace *as, QEMUBH *bh)
 
 static void address_space_notify_map_clients(AddressSpace *as)
 {
-    QEMU_LOCK_GUARD(&map_client_list_lock);
+    QEMU_LOCK_GUARD(&as->map_client_list_lock);
     address_space_notify_map_clients_locked(as);
 }
 
@@ -3219,25 +3200,25 @@ void *address_space_map(AddressSpace *as,
     mr = flatview_translate(fv, addr, &xlat, &l, is_write, attrs);
 
     if (!memory_access_is_direct(mr, is_write)) {
-        if (qatomic_xchg(&bounce.in_use, true)) {
+        if (qatomic_xchg(&as->bounce.in_use, true)) {
             *plen = 0;
             return NULL;
         }
         /* Avoid unbounded allocations */
         l = MIN(l, TARGET_PAGE_SIZE);
-        bounce.buffer = qemu_memalign(TARGET_PAGE_SIZE, l);
-        bounce.addr = addr;
-        bounce.len = l;
+        as->bounce.buffer = qemu_memalign(TARGET_PAGE_SIZE, l);
+        as->bounce.addr = addr;
+        as->bounce.len = l;
 
         memory_region_ref(mr);
-        bounce.mr = mr;
+        as->bounce.mr = mr;
         if (!is_write) {
             flatview_read(fv, addr, MEMTXATTRS_UNSPECIFIED,
-                               bounce.buffer, l);
+                          as->bounce.buffer, l);
         }
 
         *plen = l;
-        return bounce.buffer;
+        return as->bounce.buffer;
     }
 
 
@@ -3255,7 +3236,7 @@ void *address_space_map(AddressSpace *as,
 void address_space_unmap(AddressSpace *as, void *buffer, hwaddr len,
                          bool is_write, hwaddr access_len)
 {
-    if (buffer != bounce.buffer) {
+    if (buffer != as->bounce.buffer) {
         MemoryRegion *mr;
         ram_addr_t addr1;
 
@@ -3271,14 +3252,14 @@ void address_space_unmap(AddressSpace *as, void *buffer, hwaddr len,
         return;
     }
     if (is_write) {
-        address_space_write(as, bounce.addr, MEMTXATTRS_UNSPECIFIED,
-                            bounce.buffer, access_len);
+        address_space_write(as, as->bounce.addr, MEMTXATTRS_UNSPECIFIED,
+                            as->bounce.buffer, access_len);
     }
-    qemu_vfree(bounce.buffer);
-    bounce.buffer = NULL;
-    memory_region_unref(bounce.mr);
+    qemu_vfree(as->bounce.buffer);
+    as->bounce.buffer = NULL;
+    memory_region_unref(as->bounce.mr);
     /* Clear in_use before reading map_client_list.  */
-    qatomic_set_mb(&bounce.in_use, false);
+    qatomic_set_mb(&as->bounce.in_use, false);
     address_space_notify_map_clients(as);
 }
 
-- 
2.43.2

[PATCH v10 4/7] softmmu: Support concurrent bounce buffers

[Mattias Nissler]

When DMA memory can't be directly accessed, as is the case when
running the device model in a separate process without shareable DMA
file descriptors, bounce buffering is used.

It is not uncommon for device models to request mapping of several DMA
regions at the same time. Examples include:
 * net devices, e.g. when transmitting a packet that is split across
   several TX descriptors (observed with igb)
 * USB host controllers, when handling a packet with multiple data TRBs
   (observed with xhci)

Previously, qemu only provided a single bounce buffer per AddressSpace
and would fail DMA map requests while the buffer was already in use. In
turn, this would cause DMA failures that ultimately manifest as hardware
errors from the guest perspective.

This change allocates DMA bounce buffers dynamically instead of
supporting only a single buffer. Thus, multiple DMA mappings work
correctly also when RAM can't be mmap()-ed.

The total bounce buffer allocation size is limited individually for each
AddressSpace. The default limit is 4096 bytes, matching the previous
maximum buffer size. A new x-max-bounce-buffer-size parameter is
provided to configure the limit for PCI devices.

Signed-off-by: Mattias Nissler <mnissler@rivosinc.com>
---
 hw/pci/pci.c                |  8 ++++
 include/exec/memory.h       | 14 +++----
 include/hw/pci/pci_device.h |  3 ++
 system/memory.c             |  5 ++-
 system/physmem.c            | 82 ++++++++++++++++++++++++++-----------
 5 files changed, 76 insertions(+), 36 deletions(-)

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index 324c1302d2..d6f4944cbd 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -85,6 +85,8 @@ static Property pci_props[] = {
                     QEMU_PCIE_ERR_UNC_MASK_BITNR, true),
     DEFINE_PROP_BIT("x-pcie-ari-nextfn-1", PCIDevice, cap_present,
                     QEMU_PCIE_ARI_NEXTFN_1_BITNR, false),
+    DEFINE_PROP_SIZE32("x-max-bounce-buffer-size", PCIDevice,
+                     max_bounce_buffer_size, DEFAULT_MAX_BOUNCE_BUFFER_SIZE),
     DEFINE_PROP_END_OF_LIST()
 };
 
@@ -1204,6 +1206,8 @@ static PCIDevice *do_pci_register_device(PCIDevice *pci_dev,
                        "bus master container", UINT64_MAX);
     address_space_init(&pci_dev->bus_master_as,
                        &pci_dev->bus_master_container_region, pci_dev->name);
+    pci_dev->bus_master_as.max_bounce_buffer_size =
+        pci_dev->max_bounce_buffer_size;
 
     if (phase_check(PHASE_MACHINE_READY)) {
         pci_init_bus_master(pci_dev);
@@ -2633,6 +2637,10 @@ static void pci_device_class_init(ObjectClass *klass, void *data)
     k->unrealize = pci_qdev_unrealize;
     k->bus_type = TYPE_PCI_BUS;
     device_class_set_props(k, pci_props);
+    object_class_property_set_description(
+        klass, "x-max-bounce-buffer-size",
+        "Maximum buffer size allocated for bounce buffers used for mapped "
+        "access to indirect DMA memory");
 }
 
 static void pci_device_class_base_init(ObjectClass *klass, void *data)
diff --git a/include/exec/memory.h b/include/exec/memory.h
index d417d7f363..451879efbd 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -1117,13 +1117,7 @@ typedef struct AddressSpaceMapClient {
     QLIST_ENTRY(AddressSpaceMapClient) link;
 } AddressSpaceMapClient;
 
-typedef struct {
-    MemoryRegion *mr;
-    void *buffer;
-    hwaddr addr;
-    hwaddr len;
-    bool in_use;
-} BounceBuffer;
+#define DEFAULT_MAX_BOUNCE_BUFFER_SIZE (4096)
 
 /**
  * struct AddressSpace: describes a mapping of addresses to #MemoryRegion objects
@@ -1143,8 +1137,10 @@ struct AddressSpace {
     QTAILQ_HEAD(, MemoryListener) listeners;
     QTAILQ_ENTRY(AddressSpace) address_spaces_link;
 
-    /* Bounce buffer to use for this address space. */
-    BounceBuffer bounce;
+    /* Maximum DMA bounce buffer size used for indirect memory map requests */
+    size_t max_bounce_buffer_size;
+    /* Total size of bounce buffers currently allocated, atomically accessed */
+    size_t bounce_buffer_size;
     /* List of callbacks to invoke when buffers free up */
     QemuMutex map_client_list_lock;
     QLIST_HEAD(, AddressSpaceMapClient) map_client_list;
diff --git a/include/hw/pci/pci_device.h b/include/hw/pci/pci_device.h
index d3dd0f64b2..253b48a688 100644
--- a/include/hw/pci/pci_device.h
+++ b/include/hw/pci/pci_device.h
@@ -160,6 +160,9 @@ struct PCIDevice {
     /* ID of standby device in net_failover pair */
     char *failover_pair_id;
     uint32_t acpi_index;
+
+    /* Maximum DMA bounce buffer size used for indirect memory map requests */
+    uint32_t max_bounce_buffer_size;
 };
 
 static inline int pci_intx(PCIDevice *pci_dev)
diff --git a/system/memory.c b/system/memory.c
index 642a449f8c..c288ed354a 100644
--- a/system/memory.c
+++ b/system/memory.c
@@ -3174,7 +3174,8 @@ void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name)
     as->ioeventfds = NULL;
     QTAILQ_INIT(&as->listeners);
     QTAILQ_INSERT_TAIL(&address_spaces, as, address_spaces_link);
-    as->bounce.in_use = false;
+    as->max_bounce_buffer_size = DEFAULT_MAX_BOUNCE_BUFFER_SIZE;
+    as->bounce_buffer_size = 0;
     qemu_mutex_init(&as->map_client_list_lock);
     QLIST_INIT(&as->map_client_list);
     as->name = g_strdup(name ? name : "anonymous");
@@ -3184,7 +3185,7 @@ void address_space_init(AddressSpace *as, MemoryRegion *root, const char *name)
 
 static void do_address_space_destroy(AddressSpace *as)
 {
-    assert(!qatomic_read(&as->bounce.in_use));
+    assert(qatomic_read(&as->bounce_buffer_size) == 0);
     assert(QLIST_EMPTY(&as->map_client_list));
     qemu_mutex_destroy(&as->map_client_list_lock);
 
diff --git a/system/physmem.c b/system/physmem.c
index 62758202cf..242e8f27e7 100644
--- a/system/physmem.c
+++ b/system/physmem.c
@@ -3046,6 +3046,20 @@ void cpu_flush_icache_range(hwaddr start, hwaddr len)
                                      NULL, len, FLUSH_CACHE);
 }
 
+/*
+ * A magic value stored in the first 8 bytes of the bounce buffer struct. Used
+ * to detect illegal pointers passed to address_space_unmap.
+ */
+#define BOUNCE_BUFFER_MAGIC 0xb4017ceb4ffe12ed
+
+typedef struct {
+    uint64_t magic;
+    MemoryRegion *mr;
+    hwaddr addr;
+    size_t len;
+    uint8_t buffer[];
+} BounceBuffer;
+
 static void
 address_space_unregister_map_client_do(AddressSpaceMapClient *client)
 {
@@ -3071,9 +3085,9 @@ void address_space_register_map_client(AddressSpace *as, QEMUBH *bh)
     QEMU_LOCK_GUARD(&as->map_client_list_lock);
     client->bh = bh;
     QLIST_INSERT_HEAD(&as->map_client_list, client, link);
-    /* Write map_client_list before reading in_use.  */
+    /* Write map_client_list before reading bounce_buffer_size. */
     smp_mb();
-    if (!qatomic_read(&as->bounce.in_use)) {
+    if (qatomic_read(&as->bounce_buffer_size) < as->max_bounce_buffer_size) {
         address_space_notify_map_clients_locked(as);
     }
 }
@@ -3200,28 +3214,40 @@ void *address_space_map(AddressSpace *as,
     mr = flatview_translate(fv, addr, &xlat, &l, is_write, attrs);
 
     if (!memory_access_is_direct(mr, is_write)) {
-        if (qatomic_xchg(&as->bounce.in_use, true)) {
+        size_t used = qatomic_read(&as->bounce_buffer_size);
+        for (;;) {
+            hwaddr alloc = MIN(as->max_bounce_buffer_size - used, l);
+            size_t new_size = used + alloc;
+            size_t actual =
+                qatomic_cmpxchg(&as->bounce_buffer_size, used, new_size);
+            if (actual == used) {
+                l = alloc;
+                break;
+            }
+            used = actual;
+        }
+
+        if (l == 0) {
             *plen = 0;
             return NULL;
         }
-        /* Avoid unbounded allocations */
-        l = MIN(l, TARGET_PAGE_SIZE);
-        as->bounce.buffer = qemu_memalign(TARGET_PAGE_SIZE, l);
-        as->bounce.addr = addr;
-        as->bounce.len = l;
 
+        BounceBuffer *bounce = g_malloc0(l + sizeof(BounceBuffer));
+        bounce->magic = BOUNCE_BUFFER_MAGIC;
         memory_region_ref(mr);
-        as->bounce.mr = mr;
+        bounce->mr = mr;
+        bounce->addr = addr;
+        bounce->len = l;
+
         if (!is_write) {
             flatview_read(fv, addr, MEMTXATTRS_UNSPECIFIED,
-                          as->bounce.buffer, l);
+                          bounce->buffer, l);
         }
 
         *plen = l;
-        return as->bounce.buffer;
+        return bounce->buffer;
     }
 
-
     memory_region_ref(mr);
     *plen = flatview_extend_translation(fv, addr, len, mr, xlat,
                                         l, is_write, attrs);
@@ -3236,12 +3262,11 @@ void *address_space_map(AddressSpace *as,
 void address_space_unmap(AddressSpace *as, void *buffer, hwaddr len,
                          bool is_write, hwaddr access_len)
 {
-    if (buffer != as->bounce.buffer) {
-        MemoryRegion *mr;
-        ram_addr_t addr1;
+    MemoryRegion *mr;
+    ram_addr_t addr1;
 
-        mr = memory_region_from_host(buffer, &addr1);
-        assert(mr != NULL);
+    mr = memory_region_from_host(buffer, &addr1);
+    if (mr != NULL) {
         if (is_write) {
             invalidate_and_set_dirty(mr, addr1, access_len);
         }
@@ -3251,15 +3276,22 @@ void address_space_unmap(AddressSpace *as, void *buffer, hwaddr len,
         memory_region_unref(mr);
         return;
     }
+
+
+    BounceBuffer *bounce = container_of(buffer, BounceBuffer, buffer);
+    assert(bounce->magic == BOUNCE_BUFFER_MAGIC);
+
     if (is_write) {
-        address_space_write(as, as->bounce.addr, MEMTXATTRS_UNSPECIFIED,
-                            as->bounce.buffer, access_len);
-    }
-    qemu_vfree(as->bounce.buffer);
-    as->bounce.buffer = NULL;
-    memory_region_unref(as->bounce.mr);
-    /* Clear in_use before reading map_client_list.  */
-    qatomic_set_mb(&as->bounce.in_use, false);
+        address_space_write(as, bounce->addr, MEMTXATTRS_UNSPECIFIED,
+                            bounce->buffer, access_len);
+    }
+
+    qatomic_sub(&as->bounce_buffer_size, bounce->len);
+    bounce->magic = ~BOUNCE_BUFFER_MAGIC;
+    memory_region_unref(bounce->mr);
+    g_free(bounce);
+    /* Write bounce_buffer_size before reading map_client_list. */
+    smp_mb();
     address_space_notify_map_clients(as);
 }
 
-- 
2.43.2

[PATCH v10 5/7] Update subprojects/libvfio-user

[Mattias Nissler]

Brings in assorted bug fixes. The following are of particular interest
with respect to message-based DMA support:

* bb308a2 "Fix address calculation for message-based DMA"
  Corrects a bug in DMA address calculation.

* 1569a37 "Pass server->client command over a separate socket pair"
  Adds support for separate sockets for either command direction,
  addressing a bug where libvfio-user gets confused if both client and
  server send commands concurrently.

Reviewed-by: Jagannathan Raman <jag.raman@oracle.com>
Signed-off-by: Mattias Nissler <mnissler@rivosinc.com>
---
 subprojects/libvfio-user.wrap | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/subprojects/libvfio-user.wrap b/subprojects/libvfio-user.wrap
index 416955ca45..cdf0a7a375 100644
--- a/subprojects/libvfio-user.wrap
+++ b/subprojects/libvfio-user.wrap
@@ -1,4 +1,4 @@
 [wrap-git]
 url = https://gitlab.com/qemu-project/libvfio-user.git
-revision = 0b28d205572c80b568a1003db2c8f37ca333e4d7
+revision = 1569a37a54ecb63bd4008708c76339ccf7d06115
 depth = 1
-- 
2.43.2

[PATCH v10 6/7] vfio-user: Message-based DMA support

[Mattias Nissler]

Wire up support for DMA for the case where the vfio-user client does not
provide mmap()-able file descriptors, but DMA requests must be performed
via the VFIO-user protocol. This installs an indirect memory region,
which already works for pci_dma_{read,write}, and pci_dma_map works
thanks to the existing DMA bounce buffering support.

Note that while simple scenarios work with this patch, there's a known
race condition in libvfio-user that will mess up the communication
channel. See https://github.com/nutanix/libvfio-user/issues/279 for
details as well as a proposed fix.

Reviewed-by: Jagannathan Raman <jag.raman@oracle.com>
Signed-off-by: Mattias Nissler <mnissler@rivosinc.com>
---
 hw/remote/trace-events    |   2 +
 hw/remote/vfio-user-obj.c | 100 ++++++++++++++++++++++++++++++++------
 2 files changed, 87 insertions(+), 15 deletions(-)

diff --git a/hw/remote/trace-events b/hw/remote/trace-events
index 0d1b7d56a5..358a68fb34 100644
--- a/hw/remote/trace-events
+++ b/hw/remote/trace-events
@@ -9,6 +9,8 @@ vfu_cfg_read(uint32_t offset, uint32_t val) "vfu: cfg: 0x%x -> 0x%x"
 vfu_cfg_write(uint32_t offset, uint32_t val) "vfu: cfg: 0x%x <- 0x%x"
 vfu_dma_register(uint64_t gpa, size_t len) "vfu: registering GPA 0x%"PRIx64", %zu bytes"
 vfu_dma_unregister(uint64_t gpa) "vfu: unregistering GPA 0x%"PRIx64""
+vfu_dma_read(uint64_t gpa, size_t len) "vfu: DMA read 0x%"PRIx64", %zu bytes"
+vfu_dma_write(uint64_t gpa, size_t len) "vfu: DMA write 0x%"PRIx64", %zu bytes"
 vfu_bar_register(int i, uint64_t addr, uint64_t size) "vfu: BAR %d: addr 0x%"PRIx64" size 0x%"PRIx64""
 vfu_bar_rw_enter(const char *op, uint64_t addr) "vfu: %s request for BAR address 0x%"PRIx64""
 vfu_bar_rw_exit(const char *op, uint64_t addr) "vfu: Finished %s of BAR address 0x%"PRIx64""
diff --git a/hw/remote/vfio-user-obj.c b/hw/remote/vfio-user-obj.c
index d9b879e056..a15e291c9a 100644
--- a/hw/remote/vfio-user-obj.c
+++ b/hw/remote/vfio-user-obj.c
@@ -300,6 +300,63 @@ static ssize_t vfu_object_cfg_access(vfu_ctx_t *vfu_ctx, char * const buf,
     return count;
 }
 
+static MemTxResult vfu_dma_read(void *opaque, hwaddr addr, uint64_t *val,
+                                unsigned size, MemTxAttrs attrs)
+{
+    MemoryRegion *region = opaque;
+    vfu_ctx_t *vfu_ctx = VFU_OBJECT(region->owner)->vfu_ctx;
+    uint8_t buf[sizeof(uint64_t)];
+
+    trace_vfu_dma_read(region->addr + addr, size);
+
+    g_autofree dma_sg_t *sg = g_malloc0(dma_sg_size());
+    vfu_dma_addr_t vfu_addr = (vfu_dma_addr_t)(region->addr + addr);
+    if (vfu_addr_to_sgl(vfu_ctx, vfu_addr, size, sg, 1, PROT_READ) < 0 ||
+        vfu_sgl_read(vfu_ctx, sg, 1, buf) != 0) {
+        return MEMTX_ERROR;
+    }
+
+    *val = ldn_he_p(buf, size);
+
+    return MEMTX_OK;
+}
+
+static MemTxResult vfu_dma_write(void *opaque, hwaddr addr, uint64_t val,
+                                 unsigned size, MemTxAttrs attrs)
+{
+    MemoryRegion *region = opaque;
+    vfu_ctx_t *vfu_ctx = VFU_OBJECT(region->owner)->vfu_ctx;
+    uint8_t buf[sizeof(uint64_t)];
+
+    trace_vfu_dma_write(region->addr + addr, size);
+
+    stn_he_p(buf, size, val);
+
+    g_autofree dma_sg_t *sg = g_malloc0(dma_sg_size());
+    vfu_dma_addr_t vfu_addr = (vfu_dma_addr_t)(region->addr + addr);
+    if (vfu_addr_to_sgl(vfu_ctx, vfu_addr, size, sg, 1, PROT_WRITE) < 0 ||
+        vfu_sgl_write(vfu_ctx, sg, 1, buf) != 0) {
+        return MEMTX_ERROR;
+    }
+
+    return MEMTX_OK;
+}
+
+static const MemoryRegionOps vfu_dma_ops = {
+    .read_with_attrs = vfu_dma_read,
+    .write_with_attrs = vfu_dma_write,
+    .endianness = DEVICE_HOST_ENDIAN,
+    .valid = {
+        .min_access_size = 1,
+        .max_access_size = 8,
+        .unaligned = true,
+    },
+    .impl = {
+        .min_access_size = 1,
+        .max_access_size = 8,
+    },
+};
+
 static void dma_register(vfu_ctx_t *vfu_ctx, vfu_dma_info_t *info)
 {
     VfuObject *o = vfu_get_private(vfu_ctx);
@@ -308,17 +365,30 @@ static void dma_register(vfu_ctx_t *vfu_ctx, vfu_dma_info_t *info)
     g_autofree char *name = NULL;
     struct iovec *iov = &info->iova;
 
-    if (!info->vaddr) {
-        return;
-    }
-
     name = g_strdup_printf("mem-%s-%"PRIx64"", o->device,
-                           (uint64_t)info->vaddr);
+                           (uint64_t)iov->iov_base);
 
     subregion = g_new0(MemoryRegion, 1);
 
-    memory_region_init_ram_ptr(subregion, NULL, name,
-                               iov->iov_len, info->vaddr);
+    if (info->vaddr) {
+        memory_region_init_ram_ptr(subregion, OBJECT(o), name,
+                                   iov->iov_len, info->vaddr);
+    } else {
+        /*
+         * Note that I/O regions' MemoryRegionOps handle accesses of at most 8
+         * bytes at a time, and larger accesses are broken down. However,
+         * many/most DMA accesses are larger than 8 bytes and VFIO-user can
+         * handle large DMA accesses just fine, thus this size restriction
+         * unnecessarily hurts performance, in particular given that each
+         * access causes a round trip on the VFIO-user socket.
+         *
+         * TODO: Investigate how to plumb larger accesses through memory
+         * regions, possibly by amending MemoryRegionOps or by creating a new
+         * memory region type.
+         */
+        memory_region_init_io(subregion, OBJECT(o), &vfu_dma_ops, subregion,
+                              name, iov->iov_len);
+    }
 
     dma_as = pci_device_iommu_address_space(o->pci_dev);
 
@@ -330,20 +400,20 @@ static void dma_register(vfu_ctx_t *vfu_ctx, vfu_dma_info_t *info)
 static void dma_unregister(vfu_ctx_t *vfu_ctx, vfu_dma_info_t *info)
 {
     VfuObject *o = vfu_get_private(vfu_ctx);
+    MemoryRegionSection mr_section;
     AddressSpace *dma_as = NULL;
-    MemoryRegion *mr = NULL;
-    ram_addr_t offset;
 
-    mr = memory_region_from_host(info->vaddr, &offset);
-    if (!mr) {
+    dma_as = pci_device_iommu_address_space(o->pci_dev);
+
+    mr_section =
+        memory_region_find(dma_as->root, (hwaddr)info->iova.iov_base, 1);
+    if (!mr_section.mr) {
         return;
     }
 
-    dma_as = pci_device_iommu_address_space(o->pci_dev);
-
-    memory_region_del_subregion(dma_as->root, mr);
+    memory_region_del_subregion(dma_as->root, mr_section.mr);
 
-    object_unparent((OBJECT(mr)));
+    object_unparent((OBJECT(mr_section.mr)));
 
     trace_vfu_dma_unregister((uint64_t)info->iova.iov_base);
 }
-- 
2.43.2

[PATCH v10 7/7] vfio-user: Fix config space access byte order

[Mattias Nissler]

PCI config space is little-endian, so on a big-endian host we need to
perform byte swaps for values as they are passed to and received from
the generic PCI config space access machinery.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Jagannathan Raman <jag.raman@oracle.com>
Signed-off-by: Mattias Nissler <mnissler@rivosinc.com>
---
 hw/remote/vfio-user-obj.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/hw/remote/vfio-user-obj.c b/hw/remote/vfio-user-obj.c
index a15e291c9a..0e93d7a7b4 100644
--- a/hw/remote/vfio-user-obj.c
+++ b/hw/remote/vfio-user-obj.c
@@ -281,7 +281,7 @@ static ssize_t vfu_object_cfg_access(vfu_ctx_t *vfu_ctx, char * const buf,
     while (bytes > 0) {
         len = (bytes > pci_access_width) ? pci_access_width : bytes;
         if (is_write) {
-            memcpy(&val, ptr, len);
+            val = ldn_le_p(ptr, len);
             pci_host_config_write_common(o->pci_dev, offset,
                                          pci_config_size(o->pci_dev),
                                          val, len);
@@ -289,7 +289,7 @@ static ssize_t vfu_object_cfg_access(vfu_ctx_t *vfu_ctx, char * const buf,
         } else {
             val = pci_host_config_read_common(o->pci_dev, offset,
                                               pci_config_size(o->pci_dev), len);
-            memcpy(ptr, &val, len);
+            stn_le_p(ptr, len, val);
             trace_vfu_cfg_read(offset, val);
         }
         offset += len;
-- 
2.43.2

Re: [PATCH v10 1/7] system/physmem: Replace qemu_mutex_lock() calls with QEMU_LOCK_GUARD

[Peter Xu]

On Tue, May 07, 2024 at 07:34:25AM -0700, Mattias Nissler wrote:
> From: Philippe Mathieu-Daudé <philmd@linaro.org>
> 
> From: Philippe Mathieu-Daudé <philmd@linaro.org>
> 
> Simplify cpu_[un]register_map_client() and cpu_notify_map_clients()
> by replacing the pair of qemu_mutex_lock/qemu_mutex_unlock calls by
> the WITH_QEMU_LOCK_GUARD() macro.
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> Signed-off-by: Mattias Nissler <mnissler@rivosinc.com>
> Reviewed-by: Mattias Nissler <mnissler@rivosinc.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu

Re: [PATCH v10 4/7] softmmu: Support concurrent bounce buffers

[Peter Xu]

On Tue, May 07, 2024 at 07:34:28AM -0700, Mattias Nissler wrote:
> When DMA memory can't be directly accessed, as is the case when
> running the device model in a separate process without shareable DMA
> file descriptors, bounce buffering is used.
> 
> It is not uncommon for device models to request mapping of several DMA
> regions at the same time. Examples include:
>  * net devices, e.g. when transmitting a packet that is split across
>    several TX descriptors (observed with igb)
>  * USB host controllers, when handling a packet with multiple data TRBs
>    (observed with xhci)
> 
> Previously, qemu only provided a single bounce buffer per AddressSpace
> and would fail DMA map requests while the buffer was already in use. In
> turn, this would cause DMA failures that ultimately manifest as hardware
> errors from the guest perspective.
> 
> This change allocates DMA bounce buffers dynamically instead of
> supporting only a single buffer. Thus, multiple DMA mappings work
> correctly also when RAM can't be mmap()-ed.
> 
> The total bounce buffer allocation size is limited individually for each
> AddressSpace. The default limit is 4096 bytes, matching the previous
> maximum buffer size. A new x-max-bounce-buffer-size parameter is
> provided to configure the limit for PCI devices.
> 
> Signed-off-by: Mattias Nissler <mnissler@rivosinc.com>

Acked-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu

Re: [PATCH v10 0/7] Support message-based DMA in vfio-user server

[Peter Xu]

On Tue, May 07, 2024 at 07:34:24AM -0700, Mattias Nissler wrote:
> This series adds basic support for message-based DMA in qemu's vfio-user
> server. This is useful for cases where the client does not provide file
> descriptors for accessing system memory via memory mappings. My motivating use
> case is to hook up device models as PCIe endpoints to a hardware design. This
> works by bridging the PCIe transaction layer to vfio-user, and the endpoint
> does not access memory directly, but sends memory requests TLPs to the hardware
> design in order to perform DMA.
> 
> Note that more work is needed to make message-based DMA work well: qemu
> currently breaks down DMA accesses into chunks of size 8 bytes at maximum, each
> of which will be handled in a separate vfio-user DMA request message. This is
> quite terrible for large DMA accesses, such as when nvme reads and writes
> page-sized blocks for example. Thus, I would like to improve qemu to be able to
> perform larger accesses, at least for indirect memory regions. I have something
> working locally, but since this will likely result in more involved surgery and
> discussion, I am leaving this to be addressed in a separate patch.

I assume Jag will pick this up then.

Thanks,

-- 
Peter Xu

Re: [PATCH v10 0/7] Support message-based DMA in vfio-user server

[Philippe Mathieu-Daudé]

On 7/5/24 16:34, Mattias Nissler wrote:
> This series adds basic support for message-based DMA in qemu's vfio-user
> server. This is useful for cases where the client does not provide file
> descriptors for accessing system memory via memory mappings. My motivating use
> case is to hook up device models as PCIe endpoints to a hardware design. This
> works by bridging the PCIe transaction layer to vfio-user, and the endpoint
> does not access memory directly, but sends memory requests TLPs to the hardware
> design in order to perform DMA.

Patches 1-3 & 7 queued to hw-misc tree, thanks.

Re: [PATCH v10 0/7] Support message-based DMA in vfio-user server

[Mattias Nissler]

On Wed, May 8, 2024 at 11:16 PM Philippe Mathieu-Daudé
<philmd@linaro.org> wrote:
>
> On 7/5/24 16:34, Mattias Nissler wrote:
> > This series adds basic support for message-based DMA in qemu's vfio-user
> > server. This is useful for cases where the client does not provide file
> > descriptors for accessing system memory via memory mappings. My motivating use
> > case is to hook up device models as PCIe endpoints to a hardware design. This
> > works by bridging the PCIe transaction layer to vfio-user, and the endpoint
> > does not access memory directly, but sends memory requests TLPs to the hardware
> > design in order to perform DMA.
>
> Patches 1-3 & 7 queued to hw-misc tree, thanks.

Excellent, thanks for picking these up!