[PATCH v3 3/3] nvdimm: check -object memory-backend-file, readonly=on option

[Stefan Hajnoczi <stefanha@redhat.com>]

Check that -device nvdimm,unarmed=on is used when -object
memory-backend-file,readonly=on and document that -device
nvdimm,unarmed=on|off controls whether the NVDIMM appears read-only to
the guest.

Acked-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
v3:
 * Produce an error when -device nvdimm,unarmed=off is used with -object
   memory-backend-file,readonly=on instead of silently switching on
   unarmed. [Igor]
---
 docs/nvdimm.txt | 24 +++++++++++++++++-------
 hw/mem/nvdimm.c |  9 +++++++++
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/docs/nvdimm.txt b/docs/nvdimm.txt
index c2c6e441b3..0aae682be3 100644
--- a/docs/nvdimm.txt
+++ b/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=$NVDIMM_SIZE
- -device nvdimm,id=nvdimm1,memdev=mem1
+ -object memory-backend-file,id=mem1,share=on,mem-path=$PATH,size=$NVDIMM_SIZE,readonly=off
+ -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"
-   creates a backend storage of size $NVDIMM_SIZE on a file $PATH. All
-   accesses to the virtual NVDIMM device go to the file $PATH.
+ - "object memory-backend-file,id=mem1,share=on,mem-path=$PATH,
+   size=$NVDIMM_SIZE,readonly=off" creates a backend storage of size
+   $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
-   device whose storage is provided by above memory backend device.
+   "readonly=on/off" controls whether the file $PATH is opened read-only or
+   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.
diff --git a/hw/mem/nvdimm.c b/hw/mem/nvdimm.c
index 03c2201b56..e0a9d606e1 100644
--- a/hw/mem/nvdimm.c
+++ b/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);
-- 
2.29.2