Document the changes in Documentation/arm64/tagged-pointers.txt.
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
Documentation/arm64/tagged-pointers.txt | 24 ++++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)
diff --git a/Documentation/arm64/tagged-pointers.txt b/Documentation/arm64/tagged-pointers.txt
index a25a99e82bb1..ae877d185fdb 100644
--- a/Documentation/arm64/tagged-pointers.txt
+++ b/Documentation/arm64/tagged-pointers.txt
@@ -17,13 +17,21 @@ this byte for application use.
Passing tagged addresses to the kernel
--------------------------------------
-All interpretation of userspace memory addresses by the kernel assumes
-an address tag of 0x00.
+Some initial work for supporting non-zero address tags passed to the
+kernel has been done. As of now, the kernel supports tags in:
-This includes, but is not limited to, addresses found in:
+ - user fault addresses
- - pointer arguments to system calls, including pointers in structures
- passed to system calls,
+ - pointer arguments (including pointers in structures), which don't
+ describe virtual memory ranges, passed to system calls
+
+All other interpretations of userspace memory addresses by the kernel
+assume an address tag of 0x00. This includes, but is not limited to,
+addresses found in:
+
+ - pointer arguments (including pointers in structures), which describe
+ virtual memory ranges, passed to memory system calls (mmap, mprotect,
+ etc.)
- the stack pointer (sp), e.g. when interpreting it to deliver a
signal,
@@ -33,11 +41,7 @@ This includes, but is not limited to, addresses found in:
Using non-zero address tags in any of these locations may result in an
error code being returned, a (fatal) signal being raised, or other modes
-of failure.
-
-For these reasons, passing non-zero address tags to the kernel via
-system calls is forbidden, and using a non-zero address tag for sp is
-strongly discouraged.
+of failure. Using a non-zero address tag for sp is strongly discouraged.
Programs maintaining a frame pointer and frame records that use non-zero
address tags may suffer impaired or inaccurate debug and profiling
--
2.19.0.605.g01d371f741-goog
