[tip:x86/pti] x86/spectre_v2: Don't check microcode versions when running under hypervisors

[tip-bot for Konrad Rzeszutek Wilk]

Commit-ID:  36268223c1e9981d6cfc33aff8520b3bde4b8114
Gitweb:     https://git.kernel.org/tip/36268223c1e9981d6cfc33aff8520b3bde4b8114
Author:     Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
AuthorDate: Mon, 26 Feb 2018 09:35:01 -0500
Committer:  Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Thu, 8 Mar 2018 10:13:02 +0100

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

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>
CC: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/20180226213019.GE9497@xxxxxxxxxxxxxxxxxx

---
 arch/x86/kernel/cpu/intel.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index d19e903214b4..4aa9fd379390 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -144,6 +144,13 @@ 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 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_stepping == spectre_bad_microcodes[i].stepping)