[PATCH] arm(64)/kvm: improve the documentation about HVC calls

[Pingfan Liu <kernelfans@gmail.com>]

Both arm and arm64 kernel entry point have the following prerequisite:
  MMU = off, D-cache = off, I-cache = dont care.

HVC_SOFT_RESTART call should meet this prerequisite before jumping to the
new kernel.

Furthermore, on arm64, el2_setup doesn't set I+C bits and keeps EL2 MMU
off, and KVM resets them when its unload. These are achieved by
HVC_RESET_VECTORS call.

Improve the document.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: James Morse <james.morse@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: linux-doc@vger.kernel.org
Cc: linux-arm-kernel@lists.infradead.org
To: kvmarm@lists.cs.columbia.edu
---
 Documentation/virt/kvm/arm/hyp-abi.rst | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/Documentation/virt/kvm/arm/hyp-abi.rst b/Documentation/virt/kvm/arm/hyp-abi.rst
index d9eba93..a95bc30 100644
--- a/Documentation/virt/kvm/arm/hyp-abi.rst
+++ b/Documentation/virt/kvm/arm/hyp-abi.rst
@@ -40,9 +40,9 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
 
 * ::
 
-    r0/x0 = HVC_RESET_VECTORS
+    x0 = HVC_RESET_VECTORS (arm64 only)
 
-  Turn HYP/EL2 MMU off, and reset HVBAR/VBAR_EL2 to the initials
+  Disable HYP/EL2 MMU and D-cache, and reset HVBAR/VBAR_EL2 to the initials
   stubs' exception vector value. This effectively disables an existing
   hypervisor.
 
@@ -54,7 +54,7 @@ these functions (see arch/arm{,64}/include/asm/virt.h):
     x3 = x1's value when entering the next payload (arm64)
     x4 = x2's value when entering the next payload (arm64)
 
-  Mask all exceptions, disable the MMU, move the arguments into place
+  Mask all exceptions, disable the MMU and D-cache, move the arguments into place
   (arm64 only), and jump to the restart address while at HYP/EL2. This
   hypercall is not expected to return to its caller.
 
-- 
2.7.5