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>

diff --git a/exec.c b/exec.c
index ffdb5185353bdbacc613d4730228c97e229d7288..a34c34818404a4bea5ad618d0b666425d1b6abb2 100644 (file)
--- 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)

diff --git a/include/exec/memory.h b/include/exec/memory.h
index e499dc215b3021a11e981ff6d9828abcf3d7d319..27a84e0cc3460af0f2b082f2a633e0ea88730d2c 100644 (file)
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -1265,6 +1265,12 @@ void *memory_region_get_ram_ptr(MemoryRegion *mr);
  */
 void memory_region_ram_resize(MemoryRegion *mr, ram_addr_t newsize,
                               Error **errp);
+/**
+ * memory_region_do_writeback: Trigger writeback for selected address range
+ * [addr, addr + size]
+ *
+ */
+void memory_region_do_writeback(MemoryRegion *mr, hwaddr addr, hwaddr size);
 
 /**
  * memory_region_set_log: Turn dirty logging on or off for a region.

diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index bed0554f4d2a5a1d6b77552a6febf5f3b714f1f1..5adebb0bc7ccb4b47f43aff56973c4278ea46160 100644 (file)
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -174,6 +174,14 @@ void qemu_ram_free(RAMBlock *block);
 
 int qemu_ram_resize(RAMBlock *block, ram_addr_t newsize, Error **errp);
 
+void qemu_ram_writeback(RAMBlock *block, ram_addr_t start, ram_addr_t length);
+
+/* Clear whole block of mem */
+static inline void qemu_ram_block_writeback(RAMBlock *block)
+{
+    qemu_ram_writeback(block, 0, block->used_length);
+}
+
 #define DIRTY_CLIENTS_ALL     ((1 << DIRTY_MEMORY_NUM) - 1)
 #define DIRTY_CLIENTS_NOCODE  (DIRTY_CLIENTS_ALL & ~(1 << DIRTY_MEMORY_CODE))
 

diff --git a/include/qemu/cutils.h b/include/qemu/cutils.h
index b54c847e0fef8ec1d88f7503a4ed4041d192fbfe..eb59852dfdf2d25db25c89917ab3f79539b8c33d 100644 (file)
--- a/include/qemu/cutils.h
+++ b/include/qemu/cutils.h
@@ -130,6 +130,7 @@ const char *qemu_strchrnul(const char *s, int c);
 #endif
 time_t mktimegm(struct tm *tm);
 int qemu_fdatasync(int fd);
+int qemu_msync(void *addr, size_t length, int fd);
 int fcntl_setfl(int fd, int flag);
 int qemu_parse_fd(const char *param);
 int qemu_strtoi(const char *nptr, const char **endptr, int base,

diff --git a/memory.c b/memory.c
index 06484c2bff2d373c78f858b714af0777a1c5e209..0228cad38d06fd7c84bf7b2439328444b6008781 100644 (file)
--- a/memory.c
+++ b/memory.c
@@ -2207,6 +2207,18 @@ void memory_region_ram_resize(MemoryRegion *mr, ram_addr_t newsize, Error **errp
     qemu_ram_resize(mr->ram_block, newsize, errp);
 }
 
+
+void memory_region_do_writeback(MemoryRegion *mr, hwaddr addr, hwaddr size)
+{
+    /*
+     * Might be extended case needed to cover
+     * different types of memory regions
+     */
+    if (mr->ram_block && mr->dirty_log_mask) {
+        qemu_ram_writeback(mr->ram_block, addr, size);
+    }
+}
+
 /*
  * Call proper memory listeners about the change on the newly
  * added/removed CoalescedMemoryRange.

diff --git a/util/cutils.c b/util/cutils.c
index 77acadc70ac2d76f8f9baa352b6c285a155ba83d..2380165230398cc8d1aad542af4e403597601667 100644 (file)
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -164,6 +164,44 @@ int qemu_fdatasync(int fd)
 #endif
 }
 
+/**
+ * Sync changes made to the memory mapped file back to the backing
+ * storage. For POSIX compliant systems this will fallback
+ * to regular msync call. Otherwise it will trigger whole file sync
+ * (including the metadata case there is no support to skip that otherwise)
+ *
+ * @addr   - start of the memory area to be synced
+ * @length - length of the are to be synced
+ * @fd     - file descriptor for the file to be synced
+ *           (mandatory only for POSIX non-compliant systems)
+ */
+int qemu_msync(void *addr, size_t length, int fd)
+{
+#ifdef CONFIG_POSIX
+    size_t align_mask = ~(qemu_real_host_page_size - 1);
+
+    /**
+     * There are no strict reqs as per the length of mapping
+     * to be synced. Still the length needs to follow the address
+     * alignment changes. Additionally - round the size to the multiple
+     * of PAGE_SIZE
+     */
+    length += ((uintptr_t)addr & (qemu_real_host_page_size - 1));
+    length = (length + ~align_mask) & align_mask;
+
+    addr = (void *)((uintptr_t)addr & align_mask);
+
+    return msync(addr, length, MS_SYNC);
+#else /* CONFIG_POSIX */
+    /**
+     * Perform the sync based on the file descriptor
+     * The sync range will most probably be wider than the one
+     * requested - but it will still get the job done
+     */
+    return qemu_fdatasync(fd);
+#endif /* CONFIG_POSIX */
+}
+
 #ifndef _WIN32
 /* Sets a specific flag */
 int fcntl_setfl(int fd, int flag)