For legacy IBRS to work, the IBRS bit needs to be always re-written
after vmexit, even if it's already on.
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
/*
* If the guest/host SPEC_CTRL values differ, restore the host value.
+ *
+ * For legacy IBRS, the IBRS bit always needs to be written after
+ * transitioning from a less privileged predictor mode, regardless of
+ * whether the guest/host values differ.
*/
- if (vmx->spec_ctrl != hostval)
+ if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) ||
+ vmx->spec_ctrl != hostval)
native_wrmsrl(MSR_IA32_SPEC_CTRL, hostval);
barrier_nospec();