[PATCH 3.16 334/410] x86/spectre_v2: Don't check microcode versions when running under hypervisors

[Ben Hutchings]

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

commit 36268223c1e9981d6cfc33aff8520b3bde4b8114 upstream.

As:

 1) It's known that hypervisors lie about the environment anyhow (host
    mismatch)

 2) Even if the hypervisor (Xen, KVM, VMWare, etc) provided a valid
    "correct" value, it all gets to be very murky when migration happens
    (do you provide the "new" microcode of the machine?).

And in reality the cloud vendors are the ones that should make sure that
the microcode that is running is correct and we should just sing lalalala
and trust them.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Wanpeng Li <kernellwp@xxxxxxxxx>
Cc: kvm <kvm@xxxxxxxxxxxxxxx>
Cc: KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
Link: https://lkml.kernel.org/r/20180226213019.GE9497@xxxxxxxxxxxxxxxxxx
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/kernel/cpu/intel.c | 7 +++++++
 1 file changed, 7 insertions(+)

--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -68,6 +68,13 @@ static bool bad_spectre_microcode(struct
 {
 	int i;
 
+	/*
+	 * We know that the hypervisor lie to us on the microcode version so
+	 * we may as well hope that it is running the correct version.
+	 */
+	if (cpu_has(c, X86_FEATURE_HYPERVISOR))
+		return false;
+
 	for (i = 0; i < ARRAY_SIZE(spectre_bad_microcodes); i++) {
 		if (c->x86_model == spectre_bad_microcodes[i].model &&
 		    c->x86_mask == spectre_bad_microcodes[i].stepping)