x86/spectre_v2: Don't check bad microcode versions when running under hypervisors.

As:
 1) We know they lie about the env 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 believe them.

Orabug: 27601736
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Allen Pais <allen.pais@oracle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
index 04ca665116818d7922736ad2cfa396b0f10d8935..b4825d59a9b45db94b91edd60ef30a8daa45c0e1 100644 (file)
--- a/arch/x86/kernel/cpu/scattered.c
+++ b/arch/x86/kernel/cpu/scattered.c
@@ -71,6 +71,13 @@ static bool bad_spectre_microcode(struct cpuinfo_x86 *c)
 {
        int i;
 
+       /*
+        * We know that the hypervisor lie to us on the microcode version so
+        * we may as well trust that it is running the correct microcode 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)