Machine queue, 2021-02-02

Feature:
 * nvdimm: read-only file support (Stefan Hajnoczi)
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Merge remote-tracking branch 'remotes/ehabkost-gl/tags/machine-next-pull-request' into staging

Machine queue, 2021-02-02

Feature:
* nvdimm: read-only file support (Stefan Hajnoczi)

# gpg: Signature made Tue 02 Feb 2021 19:27:21 GMT
# gpg:                using RSA key 5A322FD5ABC4D3DBACCFD1AA2807936F984DC5A6
# gpg:                issuer "ehabkost@redhat.com"
# gpg: Good signature from "Eduardo Habkost <ehabkost@redhat.com>" [full]
# Primary key fingerprint: 5A32 2FD5 ABC4 D3DB ACCF  D1AA 2807 936F 984D C5A6

* remotes/ehabkost-gl/tags/machine-next-pull-request:
  nvdimm: check -object memory-backend-file, readonly=on option
  hostmem-file: add readonly=on|off option
  memory: add readonly support to memory_region_init_ram_from_file()

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

backends/hostmem-file.c

@@ -29,6 +29,7 @@ struct HostMemoryBackendFile {
     uint64_t align;
     bool discard_data;
     bool is_pmem;
+    bool readonly;
 };
 
 static void
@@ -56,7 +57,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
                                      backend->size, fb->align,
                                      (backend->share ? RAM_SHARED : 0) |
                                      (fb->is_pmem ? RAM_PMEM : 0),
-                                     fb->mem_path, errp);
+                                     fb->mem_path, fb->readonly, errp);
     g_free(name);
 #endif
 }
@@ -151,6 +152,28 @@ static void file_memory_backend_set_pmem(Object *o, bool value, Error **errp)
     fb->is_pmem = value;
 }
 
+static bool file_memory_backend_get_readonly(Object *obj, Error **errp)
+{
+    HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
+
+    return fb->readonly;
+}
+
+static void file_memory_backend_set_readonly(Object *obj, bool value,
+                                             Error **errp)
+{
+    HostMemoryBackend *backend = MEMORY_BACKEND(obj);
+    HostMemoryBackendFile *fb = MEMORY_BACKEND_FILE(obj);
+
+    if (host_memory_backend_mr_inited(backend)) {
+        error_setg(errp, "cannot change property 'readonly' of %s.",
+                   object_get_typename(obj));
+        return;
+    }
+
+    fb->readonly = value;
+}
+
 static void file_backend_unparent(Object *obj)
 {
     HostMemoryBackend *backend = MEMORY_BACKEND(obj);
@@ -182,6 +205,9 @@ file_backend_class_init(ObjectClass *oc, void *data)
         NULL, NULL);
     object_class_property_add_bool(oc, "pmem",
         file_memory_backend_get_pmem, file_memory_backend_set_pmem);
+    object_class_property_add_bool(oc, "readonly",
+        file_memory_backend_get_readonly,
+        file_memory_backend_set_readonly);
 }
 
 static void file_backend_instance_finalize(Object *o)

docs/nvdimm.txt

@@ -17,8 +17,8 @@ following command line options:
 
  -machine pc,nvdimm
  -m $RAM_SIZE,slots=$N,maxmem=$MAX_SIZE
- -object memory-backend-file,id=mem1,share=on,mem-path=$PATH,size=$NVDIMM_SIZE
+ -object memory-backend-file,id=mem1,share=on,mem-path=$PATH,size=$NVDIMM_SIZE,readonly=off
- -device nvdimm,id=nvdimm1,memdev=mem1
+ -device nvdimm,id=nvdimm1,memdev=mem1,unarmed=off
 
 Where,
 
@@ -31,9 +31,10 @@ Where,
    of normal RAM devices and vNVDIMM devices, e.g. $MAX_SIZE should be
    >= $RAM_SIZE + $NVDIMM_SIZE here.
 
- - "object memory-backend-file,id=mem1,share=on,mem-path=$PATH,size=$NVDIMM_SIZE"
+ - "object memory-backend-file,id=mem1,share=on,mem-path=$PATH,
-   creates a backend storage of size $NVDIMM_SIZE on a file $PATH. All
+   size=$NVDIMM_SIZE,readonly=off" creates a backend storage of size
-   accesses to the virtual NVDIMM device go to the file $PATH.
+   $NVDIMM_SIZE on a file $PATH. All accesses to the virtual NVDIMM device go
+   to the file $PATH.
 
    "share=on/off" controls the visibility of guest writes. If
    "share=on", then guest writes will be applied to the backend
@@ -42,8 +43,17 @@ Where,
    "share=off", then guest writes won't be applied to the backend
    file and thus will be invisible to other guests.
 
- - "device nvdimm,id=nvdimm1,memdev=mem1" creates a virtual NVDIMM
+   "readonly=on/off" controls whether the file $PATH is opened read-only or
-   device whose storage is provided by above memory backend device.
+   read/write (default).
+
+ - "device nvdimm,id=nvdimm1,memdev=mem1,unarmed=off" creates a read/write
+   virtual NVDIMM device whose storage is provided by above memory backend
+   device.
+
+   "unarmed" controls the ACPI NFIT NVDIMM Region Mapping Structure "NVDIMM
+   State Flags" Bit 3 indicating that the device is "unarmed" and cannot accept
+   persistent writes. Linux guest drivers set the device to read-only when this
+   bit is present. Set unarmed to on when the memdev has readonly=on.
 
 Multiple vNVDIMM devices can be created if multiple pairs of "-object"
 and "-device" are provided.

hw/mem/nvdimm.c

@@ -146,6 +146,15 @@ static void nvdimm_prepare_memory_region(NVDIMMDevice *nvdimm, Error **errp)
         return;
     }
 
+    if (!nvdimm->unarmed && memory_region_is_rom(mr)) {
+        HostMemoryBackend *hostmem = dimm->hostmem;
+
+        error_setg(errp, "'unarmed' property must be off since memdev %s "
+                   "is read-only",
+                   object_get_canonical_path_component(OBJECT(hostmem)));
+        return;
+    }
+
     nvdimm->nvdimm_mr = g_new(MemoryRegion, 1);
     memory_region_init_alias(nvdimm->nvdimm_mr, OBJECT(dimm),
                              "nvdimm-memory", mr, 0, pmem_size);

include/exec/memory.h

@@ -966,6 +966,7 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr,
  *             - RAM_PMEM: the memory is persistent memory
  *             Other bits are ignored now.
  * @path: the path in which to allocate the RAM.
+ * @readonly: true to open @path for reading, false for read/write.
  * @errp: pointer to Error*, to store an error if it happens.
  *
  * Note that this function does not do anything to cause the data in the
@@ -978,6 +979,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
                                       uint64_t align,
                                       uint32_t ram_flags,
                                       const char *path,
+                                      bool readonly,
                                       Error **errp);
 
 /**

include/exec/ram_addr.h

@@ -110,6 +110,7 @@ long qemu_maxrampagesize(void);
  *              - 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
+ *  @readonly: true to open @path for reading, false for read/write.
  *  @errp: pointer to Error*, to store an error if it happens
  *
  * Return:
@@ -118,9 +119,9 @@ long qemu_maxrampagesize(void);
  */
 RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
                                    uint32_t ram_flags, const char *mem_path,
-                                   Error **errp);
+                                   bool readonly, Error **errp);
 RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
-                                 uint32_t ram_flags, int fd,
+                                 uint32_t ram_flags, int fd, bool readonly,
                                  Error **errp);
 
 RAMBlock *qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,

include/qemu/mmap-alloc.h

@@ -14,6 +14,7 @@ size_t qemu_mempath_getpagesize(const char *mem_path);
  *  @size: the number of bytes to be mmaped
  *  @align: if not zero, specify the alignment of the starting mapping address;
  *          otherwise, the alignment in use will be determined by QEMU.
+ *  @readonly: true for a read-only mapping, false for read/write.
  *  @shared: map has RAM_SHARED flag.
  *  @is_pmem: map has RAM_PMEM flag.
  *
@@ -24,6 +25,7 @@ size_t qemu_mempath_getpagesize(const char *mem_path);
 void *qemu_ram_mmap(int fd,
                     size_t size,
                     size_t align,
+                    bool readonly,
                     bool shared,
                     bool is_pmem);
 

qemu-options.hx

@@ -4426,7 +4426,7 @@ SRST
     they are specified. Note that the 'id' property must be set. These
     objects are placed in the '/objects' path.
 
-    ``-object memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align``
+    ``-object memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align,readonly=on|off``
         Creates a memory file backend object, which can be used to back
         the guest RAM with huge pages.
 
@@ -4509,6 +4509,9 @@ SRST
         4.15) and the filesystem of ``mem-path`` mounted with DAX
         option.
 
+        The ``readonly`` option specifies whether the backing file is opened
+        read-only or read-write (default).
+
     ``-object memory-backend-ram,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave``
         Creates a memory backend object, which can be used to back the
         guest RAM. Memory backend objects offer more control than the

softmmu/memory.c

@@ -1587,15 +1587,18 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
                                       uint64_t align,
                                       uint32_t ram_flags,
                                       const char *path,
+                                      bool readonly,
                                       Error **errp)
 {
     Error *err = NULL;
     memory_region_init(mr, owner, name, size);
     mr->ram = true;
+    mr->readonly = readonly;
     mr->terminates = true;
     mr->destructor = memory_region_destructor_ram;
     mr->align = align;
-    mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path, &err);
+    mr->ram_block = qemu_ram_alloc_from_file(size, mr, ram_flags, path,
+                                             readonly, &err);
     if (err) {
         mr->size = int128_zero();
         object_unparent(OBJECT(mr));
@@ -1618,7 +1621,7 @@ void memory_region_init_ram_from_fd(MemoryRegion *mr,
     mr->destructor = memory_region_destructor_ram;
     mr->ram_block = qemu_ram_alloc_from_fd(size, mr,
                                            share ? RAM_SHARED : 0,
-                                           fd, &err);
+                                           fd, false, &err);
     if (err) {
         mr->size = int128_zero();
         object_unparent(OBJECT(mr));

softmmu/physmem.c

@@ -1398,6 +1398,7 @@ static int64_t get_file_align(int fd)
 
 static int file_ram_open(const char *path,
                          const char *region_name,
+                         bool readonly,
                          bool *created,
                          Error **errp)
 {
@@ -1408,7 +1409,7 @@ static int file_ram_open(const char *path,
 
     *created = false;
     for (;;) {
-        fd = open(path, O_RDWR);
+        fd = open(path, readonly ? O_RDONLY : O_RDWR);
         if (fd >= 0) {
             /* @path names an existing file, use it */
             break;
@@ -1460,6 +1461,7 @@ static int file_ram_open(const char *path,
 static void *file_ram_alloc(RAMBlock *block,
                             ram_addr_t memory,
                             int fd,
+                            bool readonly,
                             bool truncate,
                             Error **errp)
 {
@@ -1510,7 +1512,7 @@ static void *file_ram_alloc(RAMBlock *block,
         perror("ftruncate");
     }
 
-    area = qemu_ram_mmap(fd, memory, block->mr->align,
+    area = qemu_ram_mmap(fd, memory, block->mr->align, readonly,
                          block->flags & RAM_SHARED, block->flags & RAM_PMEM);
     if (area == MAP_FAILED) {
         error_setg_errno(errp, errno,
@@ -1942,7 +1944,7 @@ static void ram_block_add(RAMBlock *new_block, Error **errp, bool shared)
 
 #ifdef CONFIG_POSIX
 RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
-                                 uint32_t ram_flags, int fd,
+                                 uint32_t ram_flags, int fd, bool readonly,
                                  Error **errp)
 {
     RAMBlock *new_block;
@@ -1996,7 +1998,8 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
     new_block->used_length = size;
     new_block->max_length = size;
     new_block->flags = ram_flags;
-    new_block->host = file_ram_alloc(new_block, size, fd, !file_size, errp);
+    new_block->host = file_ram_alloc(new_block, size, fd, readonly,
+                                     !file_size, errp);
     if (!new_block->host) {
         g_free(new_block);
         return NULL;
@@ -2015,18 +2018,19 @@ RAMBlock *qemu_ram_alloc_from_fd(ram_addr_t size, MemoryRegion *mr,
 
 RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
                                    uint32_t ram_flags, const char *mem_path,
-                                   Error **errp)
+                                   bool readonly, Error **errp)
 {
     int fd;
     bool created;
     RAMBlock *block;
 
-    fd = file_ram_open(mem_path, memory_region_name(mr), &created, errp);
+    fd = file_ram_open(mem_path, memory_region_name(mr), readonly, &created,
+                       errp);
     if (fd < 0) {
         return NULL;
     }
 
-    block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, errp);
+    block = qemu_ram_alloc_from_fd(size, mr, ram_flags, fd, readonly, errp);
     if (!block) {
         if (created) {
             unlink(mem_path);

util/mmap-alloc.c

@@ -85,9 +85,11 @@ size_t qemu_mempath_getpagesize(const char *mem_path)
 void *qemu_ram_mmap(int fd,
                     size_t size,
                     size_t align,
+                    bool readonly,
                     bool shared,
                     bool is_pmem)
 {
+    int prot;
     int flags;
     int map_sync_flags = 0;
     int guardfd;
@@ -146,8 +148,9 @@ void *qemu_ram_mmap(int fd,
 
     offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) - (uintptr_t)guardptr;
 
-    ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
+    prot = PROT_READ | (readonly ? 0 : PROT_WRITE);
-               flags | map_sync_flags, fd, 0);
+
+    ptr = mmap(guardptr + offset, size, prot, flags | map_sync_flags, fd, 0);
 
     if (ptr == MAP_FAILED && map_sync_flags) {
         if (errno == ENOTSUP) {
@@ -171,8 +174,7 @@ void *qemu_ram_mmap(int fd,
          * if map failed with MAP_SHARED_VALIDATE | MAP_SYNC,
          * we will remove these flags to handle compatibility.
          */
-        ptr = mmap(guardptr + offset, size, PROT_READ | PROT_WRITE,
+        ptr = mmap(guardptr + offset, size, prot, flags, fd, 0);
-                   flags, fd, 0);
     }
 
     if (ptr == MAP_FAILED) {

util/oslib-posix.c

@@ -230,7 +230,7 @@ void *qemu_memalign(size_t alignment, size_t size)
 void *qemu_anon_ram_alloc(size_t size, uint64_t *alignment, bool shared)
 {
     size_t align = QEMU_VMALLOC_ALIGN;
-    void *ptr = qemu_ram_mmap(-1, size, align, shared, false);
+    void *ptr = qemu_ram_mmap(-1, size, align, false, shared, false);
 
     if (ptr == MAP_FAILED) {
         return NULL;