[PATCH v2] SUPPORT.md: Un-shimmed 32-bit PV guests are no longer supported

[George Dunlap <george.dunlap@xxxxxxxxxx>]

The support status of 32-bit guests doesn't seem particularly useful.

With it changed to fully unsupported outside of PV-shim, adjust the PV32
Kconfig default accordingly.

Reported-by: Jann Horn <jannh@xxxxxxxxxx>
Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2:
 - add in Kconfig from advisory, ported over c/s d23d792478d
---
 SUPPORT.md           | 9 +--------
 xen/arch/x86/Kconfig | 7 +++++--
 2 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/SUPPORT.md b/SUPPORT.md
index d0d4fc6f4f..a29680e04c 100644
--- a/SUPPORT.md
+++ b/SUPPORT.md
@@ -86,14 +86,7 @@ No hardware requirements
 
     Status, x86_64: Supported
     Status, x86_32, shim: Supported
-    Status, x86_32, without shim: Supported, with caveats
-
-Due to architectural limitations,
-32-bit PV guests must be assumed to be able to read arbitrary host memory
-using speculative execution attacks.
-Advisories will continue to be issued
-for new vulnerabilities related to un-shimmed 32-bit PV guests
-enabling denial-of-service attacks or privilege escalation attacks.
+    Status, x86_32, without shim: Supported, not security supported
 
 ### x86/HVM
 
diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
index e55e029b79..9b164db641 100644
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -55,7 +55,7 @@ config PV
 config PV32
        bool "Support for 32bit PV guests"
        depends on PV
-       default y
+       default PV_SHIM
        select COMPAT
        ---help---
          The 32bit PV ABI uses Ring1, an area of the x86 architecture which
@@ -67,7 +67,10 @@ config PV32
          reduction, or performance reasons.  Backwards compatibility can be
          provided via the PV Shim mechanism.
 
-         If unsure, say Y.
+         Note that outside of PV Shim, 32-bit PV guests are not security
+         supported anymore.
+
+         If unsure, use the default setting.
 
 config PV_LINEAR_PT
        bool "Support for PV linear pagetables"
-- 
2.30.2