From: Josh Poimboeuf jpoimboe@kernel.org
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@kernel.org Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Borislav Petkov bp@suse.de Signed-off-by: Thadeu Lima de Souza Cascardo cascardo@canonical.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Suleiman Souhlal suleiman@google.com --- arch/x86/kvm/vmx.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 951cec231e7f..babb1e5a4dfa 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -10770,9 +10770,13 @@ u64 __always_inline vmx_spec_ctrl_restore_host(struct vcpu_vmx *vmx) guestval = __rdmsr(MSR_IA32_SPEC_CTRL);
/* - * 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 (guestval != hostval) + if (cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) || + guestval != hostval) native_wrmsrl(MSR_IA32_SPEC_CTRL, hostval);
barrier_nospec();