[PATCH, RFC 61/62] x86/mktme: Document the MKTME API for anonymous memory encryption

[Kirill A. Shutemov]

From: Alison Schofield <alison.schofield@xxxxxxxxx>

Signed-off-by: Alison Schofield <alison.schofield@xxxxxxxxx>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
 Documentation/x86/mktme/index.rst         |  1 +
 Documentation/x86/mktme/mktme_encrypt.rst | 57 +++++++++++++++++++++++
 2 files changed, 58 insertions(+)
 create mode 100644 Documentation/x86/mktme/mktme_encrypt.rst

diff --git a/Documentation/x86/mktme/index.rst b/Documentation/x86/mktme/index.rst
index 8cf2b7d62091..ca3c76adc596 100644
--- a/Documentation/x86/mktme/index.rst
+++ b/Documentation/x86/mktme/index.rst
@@ -9,3 +9,4 @@ Multi-Key Total Memory Encryption (MKTME)
    mktme_mitigations
    mktme_configuration
    mktme_keys
+   mktme_encrypt
diff --git a/Documentation/x86/mktme/mktme_encrypt.rst b/Documentation/x86/mktme/mktme_encrypt.rst
new file mode 100644
index 000000000000..5cdffabc610f
--- /dev/null
+++ b/Documentation/x86/mktme/mktme_encrypt.rst
@@ -0,0 +1,57 @@
+MKTME API: system call encrypt_mprotect()
+=========================================
+
+Synopsis
+--------
+int encrypt_mprotect(void \*addr, size_t len, int prot, key_serial_t serial);
+
+Where *key_serial_t serial* is the serial number of a key allocated
+using the MKTME Key Service.
+
+Description
+-----------
+    encrypt_mprotect() encrypts the memory pages containing any part
+    of the address range in the interval specified by addr and len.
+
+    encrypt_mprotect() supports the legacy mprotect() behavior plus
+    the enabling of memory encryption. That means that in addition
+    to encrypting the memory, the protection flags will be updated
+    as requested in the call.
+
+    The *addr* and *len* must be aligned to a page boundary.
+
+    The caller must have *KEY_NEED_VIEW* permission on the key.
+
+    The range of memory that is to be protected must be mapped as
+    *ANONYMOUS*.
+
+Errors
+------
+    In addition to the Errors returned from legacy mprotect()
+    encrypt_mprotect will return:
+
+    ENOKEY *serial* parameter does not represent a valid key.
+
+    EINVAL *len* parameter is not page aligned.
+
+    EACCES Caller does not have *KEY_NEED_VIEW* permission on the key.
+
+EXAMPLE
+--------
+  Allocate an MKTME Key::
+        serial = add_key("mktme", "name", "type=cpu algorithm=aes-xts-128" @u
+
+  Map ANONYMOUS memory::
+        ptr = mmap(NULL, size, PROT_NONE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0);
+
+  Protect memory::
+        ret = syscall(SYS_encrypt_mprotect, ptr, size, PROT_READ|PROT_WRITE,
+                      serial);
+
+  Use the encrypted memory
+
+  Free memory::
+        ret = munmap(ptr, size);
+
+  Free the key resource::
+        ret = keyctl(KEYCTL_INVALIDATE, serial);
-- 
2.20.1