[PATCH 18/19] KVM: arm64: Convert ARCH_WORKAROUND_2 to arm64_get_spectre_v4_state()

[Will Deacon]

From: Marc Zyngier <maz at kernel.org>

Convert the KVM WA2 code to using the Spectre infrastructure,
making the code much more readable. It also allows us to
take SSBS into account for the mitigation.

Signed-off-by: Marc Zyngier <maz at kernel.org>
---
 arch/arm64/kvm/arm.c        |  2 +-
 arch/arm64/kvm/hypercalls.c | 23 +++++++++++++++++------
 arch/arm64/kvm/psci.c       | 19 ++++++++++++-------
 3 files changed, 30 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 0a316dee491f..dd28c325db34 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1295,7 +1295,7 @@ static void cpu_init_hyp_mode(void)
 	 * at EL2.
 	 */
 	if (this_cpu_has_cap(ARM64_SSBS) &&
-	    arm64_get_ssbd_state() == ARM64_SSBD_FORCE_DISABLE) {
+	    arm64_get_spectre_v4_state() == SPECTRE_VULNERABLE) {
 		kvm_call_hyp_nvhe(__kvm_enable_ssbs);
 	}
 }
diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
index 69e023dfafce..9824025ccc5c 100644
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c
@@ -36,13 +36,24 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
 			}
 			break;
 		case ARM_SMCCC_ARCH_WORKAROUND_2:
-			switch (arm64_get_ssbd_state()) {
-			case ARM64_SSBD_FORCE_DISABLE:
-			case ARM64_SSBD_UNKNOWN:
+			switch (arm64_get_spectre_v4_state()) {
+			case SPECTRE_VULNERABLE:
 				break;
-			case ARM64_SSBD_KERNEL:
-			case ARM64_SSBD_FORCE_ENABLE:
-			case ARM64_SSBD_MITIGATED:
+			case SPECTRE_MITIGATED:
+				/*
+				 * SSBS everywhere: Indicate no firmware
+				 * support, as the SSBS support will be
+				 * indicated to the guest and the default is
+				 * safe.
+				 *
+				 * Otherwise, expose a permanent mitigation
+				 * to the guest, and hide SSBS so that the
+				 * guest stays protected.
+				 */
+				if (cpus_have_final_cap(ARM64_SSBS))
+					break;
+				fallthrough;
+			case SPECTRE_UNAFFECTED:
 				val = SMCCC_RET_NOT_REQUIRED;
 				break;
 			}
diff --git a/arch/arm64/kvm/psci.c b/arch/arm64/kvm/psci.c
index 87e6e3818fb5..db4056ecccfd 100644
--- a/arch/arm64/kvm/psci.c
+++ b/arch/arm64/kvm/psci.c
@@ -435,14 +435,19 @@ static int get_kernel_wa_level(u64 regid)
 		}
 		return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_1_NOT_AVAIL;
 	case KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2:
-		switch (arm64_get_ssbd_state()) {
-		case ARM64_SSBD_FORCE_ENABLE:
-		case ARM64_SSBD_MITIGATED:
-		case ARM64_SSBD_KERNEL:
+		switch (arm64_get_spectre_v4_state()) {
+		case SPECTRE_MITIGATED:
+			/*
+			 * As for the hypercall discovery, we pretend we
+			 * don't have any FW mitigation if SSBS is there at
+			 * all times.
+			 */
+			if (cpus_have_final_cap(ARM64_SSBS))
+				return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL;
+			fallthrough;
+		case SPECTRE_UNAFFECTED:
 			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_REQUIRED;
-		case ARM64_SSBD_UNKNOWN:
-		case ARM64_SSBD_FORCE_DISABLE:
-		default:
+		case SPECTRE_VULNERABLE:
 			return KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2_NOT_AVAIL;
 		}
 	}
-- 
2.28.0.681.g6f77f65b4e-goog