[PATCH v6 01/64] arm64: Add ARM64_HAS_NESTED_VIRT cpufeature

Marc Zyngier
2022-01-28T12:21:04Z

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 f5a27f067db9..466d8fdbaee2 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -2391,9 +2391,14 @@
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 5bc01e62c08a..115e0e2caf9a 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -57,9 +57,14 @@
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 a46ab3b1c4d5..2fa39ce108d0 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1772,6 +1772,20 @@ 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);
@@ -2005,6 +2019,16 @@ 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 a4a0063df456..06ca11e90482 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -2209,6 +2209,11 @@ 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