qemu-options.hx: Update the reduced-phys-bits documentation

A guest only ever experiences, at most, 1 bit of reduced physical
addressing. Update the documentation to reflect this as well as change
the example value on the reduced-phys-bits option.

Fixes: a9b4942f48 ("target/i386: add Secure Encrypted Virtualization (SEV) object")
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <13a62ced1808546c1d398e2025cf85f4c94ae123.1664550870.git.thomas.lendacky@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/qemu-options.hx b/qemu-options.hx
index b5efa648bad1f34446d049a59687679f176dea0b..42fc90aae4736a4360cadc030046cff8f6758949 100644 (file)
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -5438,7 +5438,7 @@ SRST
         physical address space. The ``reduced-phys-bits`` is used to
         provide the number of bits we loose in physical address space.
         Similar to C-bit, the value is Host family dependent. On EPYC,
-        the value should be 5.
+        a guest will lose a maximum of 1 bit, so the value should be 1.
 
         The ``sev-device`` provides the device file to use for
         communicating with the SEV firmware running inside AMD Secure
@@ -5473,7 +5473,7 @@ SRST
 
              # |qemu_system_x86| \\
                  ...... \\
-                 -object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=5 \\
+                 -object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=1 \\
                  -machine ...,memory-encryption=sev0 \\
                  .....