x86/kvm/vmx: Add MDS protection when L1D Flush is not active

commit 650b68a0622f933444a6d66936abb3103029413b upstream.

CPUs which are affected by L1TF and MDS mitigate MDS with the L1D Flush on
VMENTER when updated microcode is installed.

If a CPU is not affected by L1TF or if the L1D Flush is not in use, then
MDS mitigation needs to be invoked explicitly.

For these cases, follow the host mitigation state and invoke the MDS
mitigation before VMENTER.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Jon Masters <jcm@redhat.com>
Tested-by: Jon Masters <jcm@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 4dc04dc913c3593b693b5c290eea4987e753f1b0..8412998b3440a1c4ba77f450d7cb1c8e5cf10dce 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -61,6 +61,7 @@ DEFINE_STATIC_KEY_FALSE(switch_mm_always_ibpb);
 
 /* Control MDS CPU buffer clear before returning to user space */
 DEFINE_STATIC_KEY_FALSE(mds_user_clear);
+EXPORT_SYMBOL_GPL(mds_user_clear);
 
 void __init check_bugs(void)
 {

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 75466d9417b81c7a5d63cf8031c784dcbcce4537..5e44c255de6b3d68ce02ca56fee75a6c9c53d4be 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -9206,8 +9206,11 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
 
        vmx->__launched = vmx->loaded_vmcs->launched;
 
+       /* L1D Flush includes CPU buffer clear to mitigate MDS */
        if (static_branch_unlikely(&vmx_l1d_should_flush))
                vmx_l1d_flush(vcpu);
+       else if (static_branch_unlikely(&mds_user_clear))
+               mds_clear_cpu_buffers();
 
        asm(
                /* Store host registers */