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[Qemu-devel] [PATCH 4/7 V10] hostmem-file: add the 'pmem' option


From: junyan . he
Subject: [Qemu-devel] [PATCH 4/7 V10] hostmem-file: add the 'pmem' option
Date: Tue, 17 Jul 2018 14:32:07 +0800

From: Junyan He <address@hidden>

When QEMU emulates vNVDIMM labels and migrates vNVDIMM devices, it
needs to know whether the backend storage is a real persistent memory,
in order to decide whether special operations should be performed to
ensure the data persistence.

This boolean option 'pmem' allows users to specify whether the backend
storage of memory-backend-file is a real persistent memory. If
'pmem=on', QEMU will set the flag RAM_PMEM in the RAM block of the
corresponding memory region. If 'pmem' is set while lack of libpmem
support, a error is generated.

Signed-off-by: Junyan He <address@hidden>
Signed-off-by: Haozhong Zhang <address@hidden>
Reviewed-by: Stefan Hajnoczi <address@hidden>
Reviewed-by: Igor Mammedov <address@hidden>

---
 backends/hostmem-file.c | 41 ++++++++++++++++++++++++++++++++++++++++-
 docs/nvdimm.txt         | 22 ++++++++++++++++++++++
 exec.c                  |  8 ++++++++
 include/exec/memory.h   |  4 ++++
 include/exec/ram_addr.h |  3 +++
 qemu-options.hx         |  7 +++++++
 6 files changed, 84 insertions(+), 1 deletion(-)

diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
index 34c68bb..b1a2453 100644
--- a/backends/hostmem-file.c
+++ b/backends/hostmem-file.c
@@ -12,6 +12,7 @@
 #include "qemu/osdep.h"
 #include "qapi/error.h"
 #include "qemu-common.h"
+#include "qemu/error-report.h"
 #include "sysemu/hostmem.h"
 #include "sysemu/sysemu.h"
 #include "qom/object_interfaces.h"
@@ -34,6 +35,7 @@ struct HostMemoryBackendFile {
     bool discard_data;
     char *mem_path;
     uint64_t align;
+    bool is_pmem;
 };
 
 static void
@@ -59,7 +61,8 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error 
**errp)
         memory_region_init_ram_from_file(&backend->mr, OBJECT(backend),
                                  path,
                                  backend->size, fb->align,
-                                 backend->share ? RAM_SHARED : 0,
+                                 (backend->share ? RAM_SHARED : 0) |
+                                 (fb->is_pmem ? RAM_PMEM : 0),
                                  fb->mem_path, errp);
         g_free(path);
     }
@@ -131,6 +134,39 @@ static void file_memory_backend_set_align(Object *o, 
Visitor *v,
     error_propagate(errp, local_err);
 }
 
+static bool file_memory_backend_get_pmem(Object *o, Error **errp)
+{
+    return MEMORY_BACKEND_FILE(o)->is_pmem;
+}
+
+static void file_memory_backend_set_pmem(Object *o, bool value, Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(o);
+    HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(o);
+
+    if (host_memory_backend_mr_inited(backend)) {
+        error_setg(errp, "cannot change property 'pmem' of %s '%s'",
+                   object_get_typename(o),
+                   object_get_canonical_path_component(o));
+        return;
+    }
+
+#ifndef CONFIG_LIBPMEM
+    if (value) {
+        Error *local_err = NULL;
+        error_setg(&local_err,
+                   "Lack of libpmem support while setting the 'pmem=on'"
+                   " of %s '%s'. We can't ensure data persistence.",
+                   object_get_typename(o),
+                   object_get_canonical_path_component(o));
+        error_propagate(errp, local_err);
+        return;
+    }
+#endif
+
+    fb->is_pmem = value;
+}
+
 static void file_backend_unparent(Object *obj)
 {
     HostMemoryBackend *backend = MEMORY_BACKEND(obj);
@@ -162,6 +198,9 @@ file_backend_class_init(ObjectClass *oc, void *data)
         file_memory_backend_get_align,
         file_memory_backend_set_align,
         NULL, NULL, &error_abort);
+    object_class_property_add_bool(oc, "pmem",
+        file_memory_backend_get_pmem, file_memory_backend_set_pmem,
+        &error_abort);
 }
 
 static void file_backend_instance_finalize(Object *o)
diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
index 24b443b..48754d2 100644
--- a/docs/nvdimm.txt
+++ b/docs/nvdimm.txt
@@ -173,3 +173,25 @@ There are currently two valid values for this option:
              the NVDIMMs in the event of power loss.  This implies that the
              platform also supports flushing dirty data through the memory
              controller on power loss.
+
+If the vNVDIMM backend is on the host persistent memory that can be
+accessed in SNIA NVM Programming Model [1] (e.g., Intel NVDIMM), it's
+suggested to set the 'pmem' option of memory-backend-file to 'on'. When
+'pmem' is 'on' and QEMU is built with libpmem [2] support (configured with
+--enable-libpmem), QEMU will take necessary operations to guarantee the
+persistence of its own writes to the vNVDIMM backend(e.g., in vNVDIMM label
+emulation and live migration). If 'pmem' is 'on' while there is no libpmem
+support, qemu will exit and report a "lack of libpmem support" message to
+ensure the persistence is available. For example, if we want to ensure the
+persistence for some backend file, use the QEMU command line:
+
+    -object memory-backend-file,id=nv_mem,mem-path=/XXX/yyy,size=4G,pmem=on
+
+References
+----------
+
+[1] NVM Programming Model (NPM)
+       Version 1.2
+    
https://www.snia.org/sites/default/files/technical_work/final/NVMProgrammingModel_v1.2.pdf
+[2] Persistent Memory Development Kit (PMDK), formerly known as NVML project, 
home page:
+    http://pmem.io/pmdk/
diff --git a/exec.c b/exec.c
index 1ec539d..815acc7 100644
--- a/exec.c
+++ b/exec.c
@@ -2245,6 +2245,9 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, 
MemoryRegion *mr,
     Error *local_err = NULL;
     int64_t file_size;
 
+    /* Just support these ram flags by now. */
+    assert(ram_flags == 0 || (ram_flags & (RAM_SHARED | RAM_PMEM)));
+
     if (xen_enabled()) {
         error_setg(errp, "-mem-path not supported with Xen");
         return NULL;
@@ -4072,6 +4075,11 @@ err:
     return ret;
 }
 
+bool ramblock_is_pmem(RAMBlock *rb)
+{
+    return rb->flags & RAM_PMEM;
+}
+
 #endif
 
 void page_size_init(void)
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 513ec8d..a3baa2a 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -123,6 +123,9 @@ typedef struct IOMMUNotifier IOMMUNotifier;
 /* RAM can be migrated */
 #define RAM_MIGRATABLE (1 << 4)
 
+/* RAM is a persistent kind memory */
+#define RAM_PMEM (1 << 5)
+
 static inline void iommu_notifier_init(IOMMUNotifier *n, IOMMUNotify fn,
                                        IOMMUNotifierFlag flags,
                                        hwaddr start, hwaddr end,
@@ -654,6 +657,7 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr,
  *         (getpagesize()) will be used.
  * @ram_flags: Memory region features:
  *             - RAM_SHARED: memory must be mmaped with the MAP_SHARED flag
+ *             - RAM_PMEM: the memory is persistent memory
  *             Other bits are ignored now.
  * @path: the path in which to allocate the RAM.
  * @errp: pointer to Error*, to store an error if it happens.
diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
index bb0a09b..f1f8ac0 100644
--- a/include/exec/ram_addr.h
+++ b/include/exec/ram_addr.h
@@ -70,6 +70,8 @@ static inline unsigned long int 
ramblock_recv_bitmap_offset(void *host_addr,
     return host_addr_offset >> TARGET_PAGE_BITS;
 }
 
+bool ramblock_is_pmem(RAMBlock *rb);
+
 long qemu_getrampagesize(void);
 
 /**
@@ -83,6 +85,7 @@ long qemu_getrampagesize(void);
  *  @ram_flags: specify the properties of the ram block, which can be one
  *              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
  *              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/qemu-options.hx b/qemu-options.hx
index 371c427..35d9b03 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -4070,6 +4070,13 @@ requires an alignment different than the default one 
used by QEMU, eg
 the device DAX /dev/dax0.0 requires 2M alignment rather than 4K. In
 such cases, users can specify the required alignment via this option.
 
+The @option{pmem} option specifies whether the backing file specified
+by @option{mem-path} is on the persistent memory that can be accessed
+using the SNIA NVM programming model (e.g. Intel NVDIMM).
+If @option{pmem} is set to 'on', QEMU will take necessary operations to
+guarantee the persistence of its own writes to @option{mem-path}
+(e.g. in vNVDIMM label emulation and live migration).
+
 @item -object 
memory-backend-ram,address@hidden,address@hidden|off},address@hidden|off},address@hidden|off},address@hidden|off},address@hidden,address@hidden,address@hidden|preferred|bind|interleave}
 
 Creates a memory backend object, which can be used to back the guest RAM.
-- 
2.7.4




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