Patchwork [v2,2/7] memory: Flush coalesced MMIO on selected region access

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Submitter Jan Kiszka
Date June 27, 2012, 4:27 p.m.
Message ID <35d20ce2ae928e21ff715c86f854860d164ff8c9.1340814444.git.jan.kiszka@siemens.com>
Download mbox | patch
Permalink /patch/167704/
State New
Headers show

Comments

Jan Kiszka - June 27, 2012, 4:27 p.m.
Instead of flushing pending coalesced MMIO requests on every vmexit,
this provides a mechanism to selectively flush when memory regions
related to the coalesced one are accessed. This first of all includes
the coalesced region itself but can also applied to other regions, e.g.
of the same device, by calling memory_region_set_flush_coalesced.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---
 memory.c |   21 +++++++++++++++++++++
 memory.h |   24 ++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 0 deletions(-)
Avi Kivity - June 28, 2012, 4:07 p.m.
On 06/27/2012 07:27 PM, Jan Kiszka wrote:
> Instead of flushing pending coalesced MMIO requests on every vmexit,
> this provides a mechanism to selectively flush when memory regions
> related to the coalesced one are accessed. This first of all includes
> the coalesced region itself but can also applied to other regions, e.g.
> of the same device, by calling memory_region_set_flush_coalesced.
> 
> +
> +void memory_region_clear_flush_coalesced(MemoryRegion *mr)
> +{
> +    qemu_flush_coalesced_mmio_buffer();
> +    mr->flush_coalesced_mmio = false;
> +}


This will clear the implicit flag set by set_coalesced, but also any
explicit flag set by set_flush_coalesced.  In some convoluted setup that
will never happen, this can cause breakage.  This can be addresses
either using two flags (or perhaps using the coalesced list for the
implicit flag) or by a comment in clear_coalesced's documentation.

Patch

diff --git a/memory.c b/memory.c
index aab4a31..c29a8a3 100644
--- a/memory.c
+++ b/memory.c
@@ -311,6 +311,9 @@  static void memory_region_read_accessor(void *opaque,
     MemoryRegion *mr = opaque;
     uint64_t tmp;
 
+    if (mr->flush_coalesced_mmio) {
+        qemu_flush_coalesced_mmio_buffer();
+    }
     tmp = mr->ops->read(mr->opaque, addr, size);
     *value |= (tmp & mask) << shift;
 }
@@ -325,6 +328,9 @@  static void memory_region_write_accessor(void *opaque,
     MemoryRegion *mr = opaque;
     uint64_t tmp;
 
+    if (mr->flush_coalesced_mmio) {
+        qemu_flush_coalesced_mmio_buffer();
+    }
     tmp = (*value >> shift) & mask;
     mr->ops->write(mr->opaque, addr, tmp, size);
 }
@@ -826,6 +832,7 @@  void memory_region_init(MemoryRegion *mr,
     mr->dirty_log_mask = 0;
     mr->ioeventfd_nb = 0;
     mr->ioeventfds = NULL;
+    mr->flush_coalesced_mmio = false;
 }
 
 static bool memory_region_access_valid(MemoryRegion *mr,
@@ -1176,12 +1183,15 @@  void memory_region_add_coalescing(MemoryRegion *mr,
     cmr->addr = addrrange_make(int128_make64(offset), int128_make64(size));
     QTAILQ_INSERT_TAIL(&mr->coalesced, cmr, link);
     memory_region_update_coalesced_range(mr);
+    memory_region_set_flush_coalesced(mr);
 }
 
 void memory_region_clear_coalescing(MemoryRegion *mr)
 {
     CoalescedMemoryRange *cmr;
 
+    memory_region_clear_flush_coalesced(mr);
+
     while (!QTAILQ_EMPTY(&mr->coalesced)) {
         cmr = QTAILQ_FIRST(&mr->coalesced);
         QTAILQ_REMOVE(&mr->coalesced, cmr, link);
@@ -1190,6 +1200,17 @@  void memory_region_clear_coalescing(MemoryRegion *mr)
     memory_region_update_coalesced_range(mr);
 }
 
+void memory_region_set_flush_coalesced(MemoryRegion *mr)
+{
+    mr->flush_coalesced_mmio = true;
+}
+
+void memory_region_clear_flush_coalesced(MemoryRegion *mr)
+{
+    qemu_flush_coalesced_mmio_buffer();
+    mr->flush_coalesced_mmio = false;
+}
+
 void memory_region_add_eventfd(MemoryRegion *mr,
                                target_phys_addr_t addr,
                                unsigned size,
diff --git a/memory.h b/memory.h
index 740c48e..9267423 100644
--- a/memory.h
+++ b/memory.h
@@ -133,6 +133,7 @@  struct MemoryRegion {
     bool enabled;
     bool rom_device;
     bool warning_printed; /* For reservations */
+    bool flush_coalesced_mmio;
     MemoryRegion *alias;
     target_phys_addr_t alias_offset;
     unsigned priority;
@@ -521,6 +522,29 @@  void memory_region_add_coalescing(MemoryRegion *mr,
 void memory_region_clear_coalescing(MemoryRegion *mr);
 
 /**
+ * memory_region_set_flush_coalesced: Enforce memory coalescing flush before
+ *                                    accesses.
+ *
+ * Ensure that pending coalesced MMIO request are flushed before the memory
+ * region is accessed. This property is automatically enabled for all regions
+ * passed to memory_region_set_coalescing() and memory_region_add_coalescing().
+ *
+ * @mr: the memory region to be updated.
+ */
+void memory_region_set_flush_coalesced(MemoryRegion *mr);
+
+/**
+ * memory_region_clear_flush_coalesced: Disable memory coalescing flush before
+ *                                      accesses.
+ *
+ * Clear the automatic coalesced MMIO flushing enabled via
+ * memory_region_set_flush_coalesced.
+ *
+ * @mr: the memory region to be updated.
+ */
+void memory_region_clear_flush_coalesced(MemoryRegion *mr);
+
+/**
  * memory_region_add_eventfd: Request an eventfd to be triggered when a word
  *                            is written to a location.
  *