Signed-off-by: Teddy Astie <teddy.astie@vates.tech>
---
 docs/guest-guide/x86/hypercall-abi.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/docs/guest-guide/x86/hypercall-abi.rst b/docs/guest-guide/x86/hypercall-abi.rst
index e52ed453bc..710a02895b 100644
--- a/docs/guest-guide/x86/hypercall-abi.rst
+++ b/docs/guest-guide/x86/hypercall-abi.rst
@@ -35,6 +35,10 @@ The registers used for hypercalls depends on the operating mode of the guest.
 HVM guest depends on whether the vCPU is operating in a 64bit segment or not
 [#mode]_.
 
+If `XEN_HVM_CPUID_PHYS_ADDR_ABI` is supported, HVM guests can use a alternative
+ABI where physical addresses are used for hypercall parameters instead of
+linear addresses. This ABI can be used by tagging the hypercall index with
+0x40000000.
 
 Parameters
 ----------
-- 
2.49.0



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