arm64: Use firmware to detect CPUs that are not affected by Spectre-v2

The SMCCC ARCH_WORKAROUND_1 service can indicate that although the
firmware knows about the Spectre-v2 mitigation, this particular
CPU is not vulnerable, and it is thus not necessary to call
the firmware on this CPU.

Let's use this information to our benefit.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 032f1a4..60cf87c 100644 (file)
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -230,22 +230,36 @@ static int detect_harden_bp_fw(void)
        case PSCI_CONDUIT_HVC:
                arm_smccc_1_1_hvc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
                                  ARM_SMCCC_ARCH_WORKAROUND_1, &res);
-               if ((int)res.a0 < 0)
+               switch ((int)res.a0) {
+               case 1:
+                       /* Firmware says we're just fine */
+                       return 0;
+               case 0:
+                       cb = call_hvc_arch_workaround_1;
+                       /* This is a guest, no need to patch KVM vectors */
+                       smccc_start = NULL;
+                       smccc_end = NULL;
+                       break;
+               default:
                        return -1;
-               cb = call_hvc_arch_workaround_1;
-               /* This is a guest, no need to patch KVM vectors */
-               smccc_start = NULL;
-               smccc_end = NULL;
+               }
                break;
 
        case PSCI_CONDUIT_SMC:
                arm_smccc_1_1_smc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
                                  ARM_SMCCC_ARCH_WORKAROUND_1, &res);
-               if ((int)res.a0 < 0)
+               switch ((int)res.a0) {
+               case 1:
+                       /* Firmware says we're just fine */
+                       return 0;
+               case 0:
+                       cb = call_smc_arch_workaround_1;
+                       smccc_start = __smccc_workaround_1_smc_start;
+                       smccc_end = __smccc_workaround_1_smc_end;
+                       break;
+               default:
                        return -1;
-               cb = call_smc_arch_workaround_1;
-               smccc_start = __smccc_workaround_1_smc_start;
-               smccc_end = __smccc_workaround_1_smc_end;
+               }
                break;
 
        default: