linux-kernel - [RFC PATCH v4 16/39] KVM: arm64: Make SPE available when at least one CPU supports it

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Date:   Wed, 25 Aug 2021 17:17:52 +0100
From:   Alexandru Elisei <alexandru.elisei@....com>
To:     maz@...nel.org, james.morse@....com, suzuki.poulose@....com,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        will@...nel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v4 16/39] KVM: arm64: Make SPE available when at least one CPU supports it

KVM SPE emulation requires at least one physical CPU to support SPE.
Initialize the cpumask of PEs that support SPE the first time
KVM_CAP_ARM_SPE is queried or when the first virtual machine is created,
whichever comes first.

Signed-off-by: Alexandru Elisei <alexandru.elisei@....com>
---
 arch/arm64/include/asm/kvm_spe.h | 26 ++++++++++++++++++++++++++
 arch/arm64/kvm/Makefile          |  1 +
 arch/arm64/kvm/arm.c             |  4 ++++
 arch/arm64/kvm/spe.c             | 32 ++++++++++++++++++++++++++++++++
 4 files changed, 63 insertions(+)
 create mode 100644 arch/arm64/include/asm/kvm_spe.h
 create mode 100644 arch/arm64/kvm/spe.c

diff --git a/arch/arm64/include/asm/kvm_spe.h b/arch/arm64/include/asm/kvm_spe.h
new file mode 100644
index 000000000000..328115ce0b48
--- /dev/null
+++ b/arch/arm64/include/asm/kvm_spe.h
@@ -0,0 +1,26 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2021 - ARM Ltd
+ */
+
+#ifndef __ARM64_KVM_SPE_H__
+#define __ARM64_KVM_SPE_H__
+
+#ifdef CONFIG_KVM_ARM_SPE
+DECLARE_STATIC_KEY_FALSE(kvm_spe_available);
+
+static __always_inline bool kvm_supports_spe(void)
+{
+	return static_branch_likely(&kvm_spe_available);
+}
+
+void kvm_spe_init_supported_cpus(void);
+void kvm_spe_vm_init(struct kvm *kvm);
+#else
+#define kvm_supports_spe()	(false)
+
+static inline void kvm_spe_init_supported_cpus(void) {}
+static inline void kvm_spe_vm_init(struct kvm *kvm) {}
+#endif /* CONFIG_KVM_ARM_SPE */
+
+#endif /* __ARM64_KVM_SPE_H__ */
diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index 989bb5dad2c8..86092a0f8367 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile
@@ -25,3 +25,4 @@ kvm-y := $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o $(KVM)/eventfd.o \
 	 vgic/vgic-its.o vgic/vgic-debug.o
 
 kvm-$(CONFIG_HW_PERF_EVENTS)  += pmu-emul.o
+kvm-$(CONFIG_KVM_ARM_SPE)     += spe.o
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 22544eb367f3..82cb7b5b3b45 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -35,6 +35,7 @@
 #include <asm/kvm_arm.h>
 #include <asm/kvm_asm.h>
 #include <asm/kvm_mmu.h>
+#include <asm/kvm_spe.h>
 #include <asm/kvm_emulate.h>
 #include <asm/sections.h>
 
@@ -180,6 +181,8 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 
 	set_default_spectre(kvm);
 
+	kvm_spe_vm_init(kvm);
+
 	return ret;
 out_free_stage2_pgd:
 	kvm_free_stage2_pgd(&kvm->arch.mmu);
@@ -305,6 +308,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
 		r = 1;
 		break;
 	case KVM_CAP_ARM_SPE:
+		kvm_spe_init_supported_cpus();
 		r = 0;
 		break;
 	default:
diff --git a/arch/arm64/kvm/spe.c b/arch/arm64/kvm/spe.c
new file mode 100644
index 000000000000..83f92245f881
--- /dev/null
+++ b/arch/arm64/kvm/spe.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2021 - ARM Ltd
+ */
+
+#include <linux/cpumask.h>
+#include <linux/kvm_host.h>
+#include <linux/perf/arm_pmu.h>
+
+#include <asm/kvm_spe.h>
+
+DEFINE_STATIC_KEY_FALSE(kvm_spe_available);
+
+static const cpumask_t *supported_cpus;
+
+void kvm_spe_init_supported_cpus(void)
+{
+	if (likely(supported_cpus))
+		return;
+
+	supported_cpus = arm_spe_pmu_supported_cpus();
+	BUG_ON(!supported_cpus);
+
+	if (!cpumask_empty(supported_cpus))
+		static_branch_enable(&kvm_spe_available);
+}
+
+void kvm_spe_vm_init(struct kvm *kvm)
+{
+	/* Set supported_cpus if it isn't already initialized. */
+	kvm_spe_init_supported_cpus();
+}
-- 
2.33.0