Memory: Enable writeback for given memory region

Add an option to trigger memory writeback to sync given memory region
with the corresponding backing store, case one is available.
This extends the support for persistent memory, allowing syncing on-demand.

Signed-off-by: Beata Michalska <beata.michalska@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20191121000843.24844-3-beata.michalska@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 36 insertions, 0 deletions

diff --git a/exec.c b/exec.c
index ffdb518535..a34c348184 100644
--- a/exec.c
+++ b/exec.c
@@ -65,6 +65,8 @@
 #include "exec/ram_addr.h"
 #include "exec/log.h"
 
+#include "qemu/pmem.h"
+
 #include "migration/vmstate.h"
 
 #include "qemu/range.h"
@@ -2156,6 +2158,40 @@ int qemu_ram_resize(RAMBlock *block, ram_addr_t newsize, Error **errp)
     return 0;
 }
 
+/*
+ * Trigger sync on the given ram block for range [start, start + length]
+ * with the backing store if one is available.
+ * Otherwise no-op.
+ * @Note: this is supposed to be a synchronous op.
+ */
+void qemu_ram_writeback(RAMBlock *block, ram_addr_t start, ram_addr_t length)
+{
+    void *addr = ramblock_ptr(block, start);
+
+    /* The requested range should fit in within the block range */
+    g_assert((start + length) <= block->used_length);
+
+#ifdef CONFIG_LIBPMEM
+    /* The lack of support for pmem should not block the sync */
+    if (ramblock_is_pmem(block)) {
+        pmem_persist(addr, length);
+        return;
+    }
+#endif
+    if (block->fd >= 0) {
+        /**
+         * Case there is no support for PMEM or the memory has not been
+         * specified as persistent (or is not one) - use the msync.
+         * Less optimal but still achieves the same goal
+         */
+        if (qemu_msync(addr, length, block->fd)) {
+            warn_report("%s: failed to sync memory range: start: "
+                    RAM_ADDR_FMT " length: " RAM_ADDR_FMT,
+                    __func__, start, length);
+        }
+    }
+}
+
 /* Called with ram_list.mutex held */
 static void dirty_memory_extend(ram_addr_t old_ram_size,
                                 ram_addr_t new_ram_size)