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

[patchbot@xxxxxxx]

commit c0f890cd9d5fd2c17a1e3110cb26f98c90ce8429
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Thu Apr 11 15:37:57 2024 +0100
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Fri Apr 12 15:50:28 2024 +0100

    docs/hypercall-abi: State that the hypercall page is optional
    
    Xen doesn't care (and indeed, cannot feasibly tell) whether a hypercall was
    initiated using the hypercall page or not.
    
    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>
    Reviewed-by: Stefano Stabellini <sstabellini@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 83890e1cb6..8004122ca4 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
--
generated by git-patchbot for /home/xen/git/xen.git#staging