arm64: docs: Mandate that the I-cache doesn't hold stale kernel text

Although we require that the loaded kernel Image has been cleaned to the
PoC, we neglect to spell out the state of the I-cache. Although this
should be reasonably obvious, it doesn't hurt to be explicit.

Require that the I-cache doesn't hold any stale entries for the kernel
Image at boot.
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20200423093658.10602-1-will@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>

Documentation/arm64/booting.rst

@@ -173,7 +173,8 @@ Before jumping into the kernel, the following conditions must be met:
 - Caches, MMUs
 
   The MMU must be off.
-  Instruction cache may be on or off.
+  The instruction cache may be on or off, and must not hold any stale
+  entries corresponding to the loaded kernel image.
   The address range corresponding to the loaded kernel image must be
   cleaned to the PoC. In the presence of a system cache or other
   coherent masters with caches enabled, this will typically require