[PATCH v2 09/17] KVM: arm64: Restrict KVM_ARM_VCPU_INIT and PSCI version for protected VMs
From: Fuad Tabba <fuad.tabba@linux.dev>
Date: 2026-09-07 07:01:01
Also in:
kvmarm, lkml
Subsystem:
arm64 port (aarch64 architecture), kernel virtual machine for arm64 (kvm/arm64), the rest · Maintainers:
Catalin Marinas, Will Deacon, Marc Zyngier, Oliver Upton, Linus Torvalds
EL2 masks a protected VM's vCPU features down to the set pKVM allows, so a KVM_ARM_VCPU_INIT that requests more succeeds and produces a guest without them. Reject such an init with -EINVAL. The host and EL2 both take the allowed set from kvm_pkvm_vcpu_allowed_features(). EL2 returns 1.1 for a protected guest's PSCI_VERSION whatever the host is configured for, and forwards the platform calls to the host. Require KVM_ARM_VCPU_PSCI_0_2: without it the host dispatches the forwarded calls as PSCI 0.1. Reject a KVM_REG_ARM_PSCI_VERSION write below 1.1: below it the host rejects the SYSTEM_RESET2 that EL2 advertises. KVM_CAP_ARM_PSCI is no longer advertised to protected VMs. Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev> --- arch/arm64/include/asm/kvm_pkvm.h | 25 ++++++++++++++++++++++++- arch/arm64/kvm/arm.c | 13 +++++++++++++ arch/arm64/kvm/hyp/nvhe/pkvm.c | 17 ++--------------- arch/arm64/kvm/hypercalls.c | 7 +++++++ 4 files changed, 46 insertions(+), 16 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_pkvm.h b/arch/arm64/include/asm/kvm_pkvm.h
index beea00e693a0a..5fec511eca733 100644
--- a/arch/arm64/include/asm/kvm_pkvm.h
+++ b/arch/arm64/include/asm/kvm_pkvm.h@@ -33,7 +33,6 @@ static inline bool kvm_pkvm_ext_allowed(struct kvm *kvm, long ext) { switch (ext) { case KVM_CAP_IRQCHIP: - case KVM_CAP_ARM_PSCI: case KVM_CAP_ARM_PSCI_0_2: case KVM_CAP_NR_VCPUS: case KVM_CAP_MAX_VCPUS:
@@ -53,6 +52,30 @@ static inline bool kvm_pkvm_ext_allowed(struct kvm *kvm, long ext) } } +/* + * The vCPU features a protected VM may use: checked by the host at + * KVM_ARM_VCPU_INIT, applied by EL2 when the hyp VM is created. + */ +static inline void kvm_pkvm_vcpu_allowed_features(struct kvm *kvm, + unsigned long *allowed) +{ + bitmap_zero(allowed, KVM_VCPU_MAX_FEATURES); + + set_bit(KVM_ARM_VCPU_PSCI_0_2, allowed); + + if (kvm_pkvm_ext_allowed(kvm, KVM_CAP_ARM_PMU_V3)) + set_bit(KVM_ARM_VCPU_PMU_V3, allowed); + + if (kvm_pkvm_ext_allowed(kvm, KVM_CAP_ARM_PTRAUTH_ADDRESS)) + set_bit(KVM_ARM_VCPU_PTRAUTH_ADDRESS, allowed); + + if (kvm_pkvm_ext_allowed(kvm, KVM_CAP_ARM_PTRAUTH_GENERIC)) + set_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, allowed); + + if (kvm_pkvm_ext_allowed(kvm, KVM_CAP_ARM_SVE)) + set_bit(KVM_ARM_VCPU_SVE, allowed); +} + /* * Check whether the KVM VM IOCTL is allowed in pKVM. *
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index dbe2b6c9670a9..5c2587da815ab 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c@@ -1620,6 +1620,19 @@ static int kvm_vcpu_init_check_features(struct kvm_vcpu *vcpu, if (features & ~system_supported_vcpu_features()) return -EINVAL; + /* Reject features EL2 would drop when it creates the hyp VM. */ + if (vcpu_is_protected(vcpu)) { + DECLARE_BITMAP(allowed, KVM_VCPU_MAX_FEATURES); + + kvm_pkvm_vcpu_allowed_features(vcpu->kvm, allowed); + if (!bitmap_subset(&features, allowed, KVM_VCPU_MAX_FEATURES)) + return -EINVAL; + + /* EL2 implements PSCI 1.1; the host must not dispatch as 0.1. */ + if (!test_bit(KVM_ARM_VCPU_PSCI_0_2, &features)) + return -EINVAL; + } + /* * For now make sure that both address/generic pointer authentication * features are requested by the userspace together.
diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c
index 4ce79e191ff45..bd9a59dffd0b2 100644
--- a/arch/arm64/kvm/hyp/nvhe/pkvm.c
+++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c@@ -372,23 +372,10 @@ static void pkvm_init_features_from_host(struct pkvm_hyp_vm *hyp_vm, const struc if (kvm_pkvm_ext_allowed(kvm, KVM_CAP_ARM_MTE)) kvm->arch.flags |= host_arch_flags & BIT(KVM_ARCH_FLAG_MTE_ENABLED); - bitmap_zero(allowed_features, KVM_VCPU_MAX_FEATURES); + kvm_pkvm_vcpu_allowed_features(kvm, allowed_features); - set_bit(KVM_ARM_VCPU_PSCI_0_2, allowed_features); - - if (kvm_pkvm_ext_allowed(kvm, KVM_CAP_ARM_PMU_V3)) - set_bit(KVM_ARM_VCPU_PMU_V3, allowed_features); - - if (kvm_pkvm_ext_allowed(kvm, KVM_CAP_ARM_PTRAUTH_ADDRESS)) - set_bit(KVM_ARM_VCPU_PTRAUTH_ADDRESS, allowed_features); - - if (kvm_pkvm_ext_allowed(kvm, KVM_CAP_ARM_PTRAUTH_GENERIC)) - set_bit(KVM_ARM_VCPU_PTRAUTH_GENERIC, allowed_features); - - if (kvm_pkvm_ext_allowed(kvm, KVM_CAP_ARM_SVE)) { - set_bit(KVM_ARM_VCPU_SVE, allowed_features); + if (kvm_pkvm_ext_allowed(kvm, KVM_CAP_ARM_SVE)) kvm->arch.flags |= host_arch_flags & BIT(KVM_ARCH_FLAG_GUEST_HAS_SVE); - } bitmap_and(kvm->arch.vcpu_features, host_kvm->arch.vcpu_features, allowed_features, KVM_VCPU_MAX_FEATURES);
diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
index b11b8821c9fbc..e43ed13c82bec 100644
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c@@ -580,6 +580,13 @@ int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg) wants_02 = vcpu_has_feature(vcpu, KVM_ARM_VCPU_PSCI_0_2); + /* + * EL2 advertises PSCI 1.1; the host handles the forwarded calls + * by this version. + */ + if (vcpu_is_protected(vcpu) && val < KVM_ARM_PSCI_1_1) + return -EINVAL; + switch (val) { case KVM_ARM_PSCI_0_1: if (wants_02)
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2.39.5