[RFC PATCH v5 19/38] KVM: arm64: Do not run a VCPU on a CPU without SPE

[Alexandru Elisei]

The kernel allows heterogeneous systems where FEAT_SPE is not present on
all CPUs. This presents a challenge for KVM, as it will have to touch the
SPE registers when emulating SPE for a guest, and those accesses will cause
an undefined exception if SPE is not present on the CPU.

Avoid this situation by keeping a cpumask of CPUs that the VCPU is
allowed run on, which for SPE is the reunion of all CPUs that support
SPE, and refuse to run the VCPU on a CPU which is not part of the
cpumask.

Signed-off-by: Alexandru Elisei <alexandru.elisei at arm.com>
---
 arch/arm64/include/asm/kvm_host.h |  3 +++
 arch/arm64/kvm/arm.c              | 15 +++++++++++++++
 arch/arm64/kvm/spe.c              |  2 ++
 3 files changed, 20 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 8b3faed48914..96ce98f6135d 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -405,6 +405,9 @@ struct kvm_vcpu_arch {
 		u64 last_steal;
 		gpa_t base;
 	} steal;
+
+	cpumask_var_t supported_cpus;
+	bool cpu_not_supported;
 };
 
 /* Pointer to the vcpu's SVE FFR for sve_{save,load}_state() */
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index b2997b919be2..8a7c01d1df58 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -351,6 +351,9 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
 
 	vcpu->arch.mmu_page_cache.gfp_zero = __GFP_ZERO;
 
+	if (!zalloc_cpumask_var(&vcpu->arch.supported_cpus, GFP_KERNEL))
+		return -ENOMEM;
+
 	/* Set up the timer */
 	kvm_timer_vcpu_init(vcpu);
 
@@ -378,6 +381,7 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
 	if (vcpu->arch.has_run_once && unlikely(!irqchip_in_kernel(vcpu->kvm)))
 		static_branch_dec(&userspace_irqchip_in_use);
 
+	free_cpumask_var(vcpu->arch.supported_cpus);
 	kvm_mmu_free_memory_cache(&vcpu->arch.mmu_page_cache);
 	kvm_timer_vcpu_terminate(vcpu);
 	kvm_pmu_vcpu_destroy(vcpu);
@@ -456,6 +460,10 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 	if (vcpu_has_ptrauth(vcpu))
 		vcpu_ptrauth_disable(vcpu);
 	kvm_arch_vcpu_load_debug_state_flags(vcpu);
+
+	if (!cpumask_empty(vcpu->arch.supported_cpus) &&
+	    !cpumask_test_cpu(smp_processor_id(), vcpu->arch.supported_cpus))
+		vcpu->arch.cpu_not_supported = true;
 }
 
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
@@ -893,6 +901,13 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
 		 */
 		preempt_disable();
 
+		if (unlikely(vcpu->arch.cpu_not_supported)) {
+			vcpu->arch.cpu_not_supported = false;
+			ret = -ENOEXEC;
+			preempt_enable();
+			continue;
+		}
+
 		kvm_pmu_flush_hwstate(vcpu);
 
 		local_irq_disable();
diff --git a/arch/arm64/kvm/spe.c b/arch/arm64/kvm/spe.c
index 7c6f94358cc1..f3863728bab6 100644
--- a/arch/arm64/kvm/spe.c
+++ b/arch/arm64/kvm/spe.c
@@ -40,5 +40,7 @@ int kvm_spe_vcpu_enable_spe(struct kvm_vcpu *vcpu)
 	if (vcpu_has_feature(vcpu, KVM_ARM_VCPU_EL1_32BIT))
 		return -EINVAL;
 
+	cpumask_copy(vcpu->arch.supported_cpus, &supported_cpus);
+
 	return 0;
 }
-- 
2.33.1