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From:   Jeremy Linton <jeremy.linton@arm.com>
To:     linux-arm-kernel@lists.infradead.org
Cc:     catalin.marinas@arm.com, will.deacon@arm.com, marc.zyngier@arm.com,
        suzuki.poulose@arm.com, dave.martin@arm.com,
        shankerd@codeaurora.org, linux-kernel@vger.kernel.org,
        ykaukab@suse.de, julien.thierry@arm.com, mlangsdo@redhat.com,
        steven.price@arm.com, stefan.wahren@i2se.com,
        Jeremy Linton <jeremy.linton@arm.com>
Subject: [PATCH v4 09/12] arm64: Use firmware to detect CPUs that are not affected by Spectre-v2
Date:   Fri, 25 Jan 2019 12:07:08 -0600
Message-Id: <20190125180711.1970973-10-jeremy.linton@arm.com>
In-Reply-To: <20190125180711.1970973-1-jeremy.linton@arm.com>
References: <20190125180711.1970973-1-jeremy.linton@arm.com>
Sender: linux-kernel-owner@vger.kernel.org
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From: Marc Zyngier <marc.zyngier@arm.com>

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>
---
 arch/arm64/kernel/cpu_errata.c | 32 +++++++++++++++++++++++---------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 4d23b4d4cfa8..024c83ffff99 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -217,22 +217,36 @@ 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:
-- 
2.17.2