[Xen-devel] [PATCH] x86/msr: further correct the emulation behaviour of MSR_PRED_CMD

["Jan Beulich" <JBeulich@xxxxxxxx>]

Following commit a6aa678fa3 ("x86/msr: Correct the emulation behaviour
of MSR_PRED_CMD") we may end up writing the low bit with the wrong
value. While it's unlikely for a guest to want to write zero there, we
should still permit (this without incurring the overhead of an actual
barrier). Correcting this right away will also help whenever further
bits in the MSR might become defined.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/msr.c
+++ b/xen/arch/x86/msr.c
@@ -247,7 +247,7 @@ int guest_wrmsr(struct vcpu *v, uint32_t
             goto gp_fault; /* Rsvd bit set? */
 
         if ( v == curr )
-            wrmsrl(MSR_PRED_CMD, PRED_CMD_IBPB);
+            wrmsrl(MSR_PRED_CMD, val);
         break;
 
     case MSR_INTEL_MISC_FEATURES_ENABLES:



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