[PATCH] docs/hypercall-abi: State that the hypercall page is optional

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Xen doesn't care (and indeed, cannot feasibly tell) whether a hypercall was
initiated from inside or outside a hypercall page.

For SEV-SNP/TDX encrypted VMs, use of a hypercall page would violate the
integrity properties wanted.

Explicitly state that the hypercall page is optional.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: George Dunlap <George.Dunlap@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien@xxxxxxx>
CC: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---
 docs/guest-guide/x86/hypercall-abi.rst | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/docs/guest-guide/x86/hypercall-abi.rst 
b/docs/guest-guide/x86/hypercall-abi.rst
index 83890e1cb613..8004122ca49d 100644
--- a/docs/guest-guide/x86/hypercall-abi.rst
+++ b/docs/guest-guide/x86/hypercall-abi.rst
@@ -79,7 +79,8 @@ Hypercall Page
 ==============
 
 The hypercall page is a page of guest RAM into which Xen will write suitable
-transfer stubs.
+transfer stubs.  It is intended as a convenience for guests, but use of the
+hypercall page is not mandatory for making hypercalls to Xen.
 
 Creating a hypercall page is an isolated operation from Xen's point of view.
 It is the guests responsibility to ensure that the hypercall page, once

base-commit: 6cb501e3e6db36b1b4b6345f5af8adc0a291b404
-- 
2.30.2