[PATCH v2 1/1] s390/uv: New param workpage for the uv_get_secret_metadata() function

[Harald Freudenberger <freude@linux.ibm.com>]

The pkey uv handler may be called in a do-not-allocate memory
situation. For example when an encrypted swap file is used and the
encryption is done via UV retrievable secrets with protected keys.

The pkey uv handler calls uv_get_secret_metadata() and thus has a need
to have this function work without memory allocations. So this patch
extends the uv_get_secret_metadata() function to be able to work on
a provided working page instead of allocating/freeing memory via
kmalloc/kfree:

int uv_get_secret_metadata(const u8 secret_id[UV_SECRET_ID_LEN],
			   struct uv_secret_list_item_hdr *secret,
			   u8 *workpage);

Parameter workpage is a ephemeral working page used by the function.
If given (!= NULL), it needs to point to memory of at least PAGE_SIZE
bytes. If NULL, the function uses kmalloc/kfree to allocate and free a
working buffer.

Signed-off-by: Harald Freudenberger <freude@linux.ibm.com>
---
 arch/s390/include/asm/uv.h |  3 ++-
 arch/s390/kernel/uv.c      | 12 +++++++++---
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
index b11f5b6d0bd1..496cd9c9f2a5 100644
--- a/arch/s390/include/asm/uv.h
+++ b/arch/s390/include/asm/uv.h
@@ -617,7 +617,8 @@ static inline int uv_remove_shared(unsigned long addr)
 }
 
 int uv_get_secret_metadata(const u8 secret_id[UV_SECRET_ID_LEN],
-			   struct uv_secret_list_item_hdr *secret);
+			   struct uv_secret_list_item_hdr *secret,
+			   u8 *workpage);
 int uv_retrieve_secret(u16 secret_idx, u8 *buf, size_t buf_size);
 
 extern int prot_virt_host;
diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
index 9f05df2da2f7..0a8a6bc19c49 100644
--- a/arch/s390/kernel/uv.c
+++ b/arch/s390/kernel/uv.c
@@ -713,6 +713,9 @@ static int find_secret(const u8 secret_id[UV_SECRET_ID_LEN],
  * uv_get_secret_metadata() - get secret metadata for a given secret id.
  * @secret_id: search pattern.
  * @secret: output data, containing the secret's metadata.
+ * @workpage: ephemeral working page. Caller may give a ptr to one page
+ *            here as ephemeral working buffer. If NULL, kmalloc is used
+ *            to alloc a working buffer.
  *
  * Search for a secret with the given secret_id in the Ultravisor secret store.
  *
@@ -725,16 +728,19 @@ static int find_secret(const u8 secret_id[UV_SECRET_ID_LEN],
  * * %EIO:	- Other unexpected UV error.
  */
 int uv_get_secret_metadata(const u8 secret_id[UV_SECRET_ID_LEN],
-			   struct uv_secret_list_item_hdr *secret)
+			   struct uv_secret_list_item_hdr *secret,
+			   u8 *workpage)
 {
 	struct uv_secret_list *buf;
 	int rc;
 
-	buf = kzalloc(sizeof(*buf), GFP_KERNEL);
+	buf = workpage ? (struct uv_secret_list *)workpage :
+		kzalloc(sizeof(*buf), GFP_KERNEL);
 	if (!buf)
 		return -ENOMEM;
 	rc = find_secret(secret_id, buf, secret);
-	kfree(buf);
+	if (!workpage)
+		kfree(buf);
 	return rc;
 }
 EXPORT_SYMBOL_GPL(uv_get_secret_metadata);
-- 
2.43.0