[Xen-devel] [PATCH] Choose retpoline only when it is safe to use

[Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>]

When ( ibrs && thunk == THUNK_DEFAULT && !retpoline_safe() ) is true,
thunk is set to THUNK_JMP rather than THUNK_RETPOLINE.

When (!ibrs && thunk == THUNK_DEFAULT && !retpoline_safe() ) is true,
we should do the same.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@xxxxxxxxxx>
---
 xen/arch/x86/spec_ctrl.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index f10ffbf..ab4b244 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -247,10 +247,10 @@ void __init init_speculation_mitigations(void)
 
     /*
      * If there are still no thunk preferences, the compiled default is
-     * actually retpoline, and it is better than nothing.
+     * actually retpoline, and it is better than nothing if it's retpoline 
safe.
      */
     if ( thunk == THUNK_DEFAULT )
-        thunk = THUNK_RETPOLINE;
+        thunk = retpoline_safe() ? THUNK_RETPOLINE : THUNK_JMP;
 
     /* Apply the chosen settings. */
     if ( thunk == THUNK_LFENCE )
-- 
1.7.3

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