Documentation/vmcoreinfo: Add documentation for 'KERNELPACMASK'

Add documentation for KERNELPACMASK variable being added to the vmcoreinfo.

It indicates the PAC bits mask information of signed kernel pointers if
Armv8.3-A Pointer Authentication feature is present.

Signed-off-by: Amit Daniel Kachhap <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Will Deacon <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Dave Young <[email protected]>
Cc: Baoquan He <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

Author: amitdanielkachhap

Documentation/admin-guide/kdump/vmcoreinfo.rst

@@ -393,6 +393,12 @@ KERNELOFFSET
 The kernel randomization offset. Used to compute the page offset. If
 KASLR is disabled, this value is zero.
 
+KERNELPACMASK
+-------------
+
+The mask to extract the Pointer Authentication Code from a kernel virtual
+address.
+
 arm
 ===