From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> commit bea7e31a5caccb6fe8ed989c065072354f0ecb52 upstream. 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@xxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Signed-off-by: Borislav Petkov <bp@xxxxxxx> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@xxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/x86/kvm/vmx/vmx.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -6685,8 +6685,13 @@ void noinstr vmx_spec_ctrl_restore_host( /* * 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();
