[PATCH v5 06/69] arm64: Add ARM64_HAS_NESTED_VIRT cpufeature

[Marc Zyngier <maz@kernel.org>]

From: Jintack Lim <jintack.lim@linaro.org>

Add a new ARM64_HAS_NESTED_VIRT feature to indicate that the
CPU has the ARMv8.3 nested virtualization capability, together
with the 'kvm-arm.mode=nested' command line option.

This will be used to support nested virtualization in KVM.

Signed-off-by: Jintack Lim <jintack.lim@linaro.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
[maz: moved the command-line option to kvm-arm.mode]
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 .../admin-guide/kernel-parameters.txt         |  7 +++++-
 arch/arm64/include/asm/kvm_host.h             |  5 ++++
 arch/arm64/kernel/cpufeature.c                | 24 +++++++++++++++++++
 arch/arm64/kvm/arm.c                          |  5 ++++
 arch/arm64/tools/cpucaps                      |  1 +
 5 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9725c546a0d4..008d567b042f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2380,9 +2380,14 @@
 				   state is kept private from the host.
 				   Not valid if the kernel is running in EL2.
 
+			nested: VHE-based mode with support for nested
+				virtualization. Requires at least ARMv8.3
+				hardware.
+
 			Defaults to VHE/nVHE based on hardware support. Setting
 			mode to "protected" will disable kexec and hibernation
-			for the host.
+			for the host. "nested" is experimental and should be
+			used with extreme caution.
 
 	kvm-arm.vgic_v3_group0_trap=
 			[KVM,ARM] Trap guest accesses to GICv3 group-0
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 2a5f7f38006f..20d7cb450ef3 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -58,9 +58,14 @@
 enum kvm_mode {
 	KVM_MODE_DEFAULT,
 	KVM_MODE_PROTECTED,
+	KVM_MODE_NV,
 	KVM_MODE_NONE,
 };
+#ifdef CONFIG_KVM
 enum kvm_mode kvm_get_mode(void);
+#else
+static inline enum kvm_mode kvm_get_mode(void) { return KVM_MODE_NONE; };
+#endif
 
 DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
 
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 6f3e677d88f1..4d57e98cdde5 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1761,6 +1761,20 @@ static void cpu_copy_el2regs(const struct arm64_cpu_capabilities *__unused)
 		write_sysreg(read_sysreg(tpidr_el1), tpidr_el2);
 }
 
+static bool has_nested_virt_support(const struct arm64_cpu_capabilities *cap,
+				    int scope)
+{
+	if (kvm_get_mode() != KVM_MODE_NV)
+		return false;
+
+	if (!has_cpuid_feature(cap, scope)) {
+		pr_warn("unavailable: %s\n", cap->desc);
+		return false;
+	}
+
+	return true;
+}
+
 static void cpu_has_fwb(const struct arm64_cpu_capabilities *__unused)
 {
 	u64 val = read_sysreg_s(SYS_CLIDR_EL1);
@@ -1994,6 +2008,16 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.matches = runs_at_el2,
 		.cpu_enable = cpu_copy_el2regs,
 	},
+	{
+		.desc = "Nested Virtualization Support",
+		.capability = ARM64_HAS_NESTED_VIRT,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.matches = has_nested_virt_support,
+		.sys_reg = SYS_ID_AA64MMFR2_EL1,
+		.sign = FTR_UNSIGNED,
+		.field_pos = ID_AA64MMFR2_NV_SHIFT,
+		.min_field_value = 1,
+	},
 	{
 		.capability = ARM64_HAS_32BIT_EL0_DO_NOT_USE,
 		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 2f03cbfefe67..68da54d58cd0 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -2174,6 +2174,11 @@ static int __init early_kvm_mode_cfg(char *arg)
 		return 0;
 	}
 
+	if (strcmp(arg, "nested") == 0 && !WARN_ON(!is_kernel_in_hyp_mode())) {
+		kvm_mode = KVM_MODE_NV;
+		return 0;
+	}
+
 	if (strcmp(arg, "none") == 0) {
 		kvm_mode = KVM_MODE_NONE;
 		return 0;
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 870c39537dd0..a49864b56a07 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -26,6 +26,7 @@ HAS_GENERIC_AUTH_IMP_DEF
 HAS_IRQ_PRIO_MASKING
 HAS_LDAPR
 HAS_LSE_ATOMICS
+HAS_NESTED_VIRT
 HAS_NO_FPSIMD
 HAS_NO_HW_PREFETCH
 HAS_PAN
-- 
2.30.2