[patch V6 08/14] MDS basics 8

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 explicit.

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

Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Greg Kroah-Hartman <[email protected]>
---
V4 --> V5: Fix changelog
---
 arch/x86/kernel/cpu/bugs.c |    1 +
 arch/x86/kvm/vmx/vmx.c     |    2 ++
 2 files changed, 3 insertions(+)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -65,6 +65,7 @@ DEFINE_STATIC_KEY_FALSE(switch_mm_always
 
 /* 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)
 {
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -6371,6 +6371,8 @@ static void __vmx_vcpu_run(struct kvm_vc
 
 	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 */