Merge tag 'virtio-mem-for-5.16' of git://github.com/davidhildenbrand/linux
Pull virtio-mem update from David Hildenbrand:
"Support the VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE feature in virtio-mem,
now that "accidential" access to logically unplugged memory inside
added Linux memory blocks is no longer possible, because we:
- Removed /dev/kmem in commit bbcd53c96071 ("drivers/char: remove
/dev/kmem for good")
- Disallowed access to virtio-mem device memory via /dev/mem in
commit 2128f4e21aa ("virtio-mem: disallow mapping virtio-mem memory
via /dev/mem")
- Sanitized access to virtio-mem device memory via /proc/kcore in
commit 0daa322b8ff9 ("fs/proc/kcore: don't read offline sections,
logically offline pages and hwpoisoned pages")
- Sanitized access to virtio-mem device memory via /proc/vmcore in
commit ce2814622e84 ("virtio-mem: kdump mode to sanitize
/proc/vmcore access")
The new VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE feature that will be
required by some hypervisors implementing virtio-mem in the near
future, so let's support it now that we safely can"
* tag 'virtio-mem-for-5.16' of git://github.com/davidhildenbrand/linux:
virtio-mem: support VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE
diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 0da0af2..96e5a87 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -2889,6 +2889,7 @@ static unsigned int virtio_mem_features[] = {
#if defined(CONFIG_NUMA) && defined(CONFIG_ACPI_NUMA)
VIRTIO_MEM_F_ACPI_PXM,
#endif
+ VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE,
};
static const struct virtio_device_id virtio_mem_id_table[] = {
diff --git a/include/uapi/linux/virtio_mem.h b/include/uapi/linux/virtio_mem.h
index 70e01c6..e9122f1 100644
--- a/include/uapi/linux/virtio_mem.h
+++ b/include/uapi/linux/virtio_mem.h
@@ -68,9 +68,10 @@
* explicitly triggered (VIRTIO_MEM_REQ_UNPLUG).
*
* There are no guarantees what will happen if unplugged memory is
- * read/written. Such memory should, in general, not be touched. E.g.,
- * even writing might succeed, but the values will simply be discarded at
- * random points in time.
+ * read/written. In general, unplugged memory should not be touched, because
+ * the resulting action is undefined. There is one exception: without
+ * VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE, unplugged memory inside the usable
+ * region can be read, to simplify creation of memory dumps.
*
* It can happen that the device cannot process a request, because it is
* busy. The device driver has to retry later.
@@ -87,6 +88,8 @@
/* node_id is an ACPI PXM and is valid */
#define VIRTIO_MEM_F_ACPI_PXM 0
+/* unplugged memory must not be accessed */
+#define VIRTIO_MEM_F_UNPLUGGED_INACCESSIBLE 1
/* --- virtio-mem: guest -> host requests --- */
