When a file supporting DAX is used as vNVDIMM backend, mmap it with
MAP_SYNC flag in addition can guarantee the persistence of guest write
to the backend file without other QEMU actions (e.g., periodic fsync()
by QEMU).
A set of RAM_SYNC flags are added to qemu_ram_mmap():
Signed-off-by: Haozhong Zhang <haozhong.zh...@intel.com>
Signed-off-by: Zhang Yi <yi.z.zh...@linux.intel.com>
---
exec.c | 2 +-
include/exec/memory.h | 3 +++
include/exec/ram_addr.h | 1 +
include/qemu/mmap-alloc.h | 1 +
include/qemu/osdep.h | 29 +++++++++++++++++++++++++++++
util/mmap-alloc.c | 13 +++++++++----
6 files changed, 44 insertions(+), 5 deletions(-)
diff --git a/exec.c b/exec.c
index e92a7da..dc4d180 100644
--- a/exec.c
+++ b/exec.c
@@ -2241,7 +2241,7 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size,
MemoryRegion *mr,
int64_t file_size;
/* Just support these ram flags by now. */
- assert((ram_flags & ~(RAM_SHARED | RAM_PMEM)) == 0);
+ assert((ram_flags & ~(RAM_SHARED | RAM_PMEM | RAM_SYNC)) == 0);
if (xen_enabled()) {
error_setg(errp, "-mem-path not supported with Xen");
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 667466b..33a4e2c 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -126,6 +126,9 @@ typedef struct IOMMUNotifier IOMMUNotifier;
/* RAM is a persistent kind memory */
#define RAM_PMEM (1 << 5)
+/* RAM can be mmap by a MAP_SYNC flag */
+#define RAM_SYNC (1 << 6)
+
static inline void iommu_notifier_init(IOMMUNotifier *n, IOMMUNotify fn,
IOMMUNotifierFlag flags,
hwaddr start, hwaddr end,
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index 9ecd911..d239ce7 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -87,6 +87,7 @@ long qemu_getrampagesize(void);
* or bit-or of following values
* - RAM_SHARED: mmap the backing file or device with MAP_SHARED
* - RAM_PMEM: the backend @mem_path or @fd is persistent memory
+ * - RAM_SYNC: mmap with MAP_SYNC flag
* Other bits are ignored.
* @mem_path or @fd: specify the backing file or device
* @errp: pointer to Error*, to store an error if it happens
diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
index 6fe6ed4..1755a8b 100644
--- a/include/qemu/mmap-alloc.h
+++ b/include/qemu/mmap-alloc.h
@@ -18,6 +18,7 @@ size_t qemu_mempath_getpagesize(const char *mem_path);
* @flags: specifies additional properties of the mapping, which can be one or
* bit-or of following values
* - RAM_SHARED: mmap with MAP_SHARED flag
+ * - RAM_SYNC: mmap with MAP_SYNC flag
* Other bits are ignored.
*
* Return:
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 3bf48bc..f94ea68 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -410,6 +410,35 @@ void qemu_anon_ram_free(void *ptr, size_t size);
# define QEMU_VMALLOC_ALIGN getpagesize()
#endif
+/*
+ * MAP_SHARED_VALIDATE and MAP_SYNC are introduced in Linux kernel
+ * 4.15, so they may not be defined when compiling on older kernels.
+ */
+#ifdef CONFIG_LINUX
+
+#include <sys/mman.h>
+
+#ifndef MAP_SHARED_VALIDATE
+#define MAP_SHARED_VALIDATE 0x3
+#endif
+
+#ifndef MAP_SYNC
+#define MAP_SYNC 0x80000
+#endif
+
+/* MAP_SYNC is only available with MAP_SHARED_VALIDATE. */
+#define MAP_SYNC_FLAGS (MAP_SYNC | MAP_SHARED_VALIDATE)
+
+#else /* !CONFIG_LINUX */
+
+#define MAP_SHARED_VALIDATE 0x0
+#define MAP_SYNC 0x0
+
+#define QEMU_HAS_MAP_SYNC false
+#define MAP_SYNC_FLAGS 0
+
+#endif /* CONFIG_LINUX */
+
#ifdef CONFIG_POSIX
struct qemu_signalfd_siginfo {
uint32_t ssi_signo; /* Signal number */
diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
index 8f0a740..025ab6a 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -99,6 +99,7 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align,
uint32_t flags)
void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
#endif
bool shared = flags & RAM_SHARED;
+ int mmap_xflags = 0;
size_t offset;
void *ptr1;
@@ -109,16 +110,20 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align,
uint32_t flags)
assert(is_power_of_2(align));
/* Always align to host page size */
assert(align >= getpagesize());
+ if ((flags & RAM_SYNC) && shared) {
+ mmap_xflags |= MAP_SYNC_FLAGS;
+ }
offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
+ retry_mmap_fd:
ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
MAP_FIXED |
(fd == -1 ? MAP_ANONYMOUS : 0) |
- (shared ? MAP_SHARED : MAP_PRIVATE),
+ (shared ? MAP_SHARED : MAP_PRIVATE) | mmap_xflags,
fd, 0);
- if (ptr1 == MAP_FAILED) {
- munmap(ptr, total);
- return MAP_FAILED;
+ if ((ptr1 == MAP_FAILED) && (mmap_xflags & MAP_SYNC_FLAGS)) {
+ mmap_xflags &= ~MAP_SYNC_FLAGS;
+ goto retry_mmap_fd;
}
if (offset > 0) {
--
2.7.4
