[RFC PATCH v2 04/28] KVM: arm64: Keep consistency of ID registers between vCPUs

[Reiji Watanabe]

All vCPUs that are owned by a VM must have the same values of ID
registers.

Return an error at the very first KVM_RUN for a vCPU if the vCPU has
different values in any ID registers from any other vCPUs that have
already started KVM_RUN once.  Also, return an error if userspace
tries to change a value of ID register for a vCPU that already
started KVM_RUN once.

Changing ID register is still not allowed at present though.

Signed-off-by: Reiji Watanabe <reijiw at google.com>
---
 arch/arm64/include/asm/kvm_host.h |  2 ++
 arch/arm64/kvm/arm.c              |  4 ++++
 arch/arm64/kvm/sys_regs.c         | 31 +++++++++++++++++++++++++++++++
 3 files changed, 37 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 0cd351099adf..69af669308b0 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -745,6 +745,8 @@ int kvm_arm_vcpu_arch_has_attr(struct kvm_vcpu *vcpu,
 long kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
 				struct kvm_arm_copy_mte_tags *copy_tags);
 
+int kvm_id_regs_consistency_check(const struct kvm_vcpu *vcpu);
+
 /* Guest/host FPSIMD coordination helpers */
 int kvm_arch_vcpu_run_map_fp(struct kvm_vcpu *vcpu);
 void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu);
diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index fe102cd2e518..83cedd74de73 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -595,6 +595,10 @@ static int kvm_vcpu_first_run_init(struct kvm_vcpu *vcpu)
 		return -EPERM;
 
 	vcpu->arch.has_run_once = true;
+	if (kvm_id_regs_consistency_check(vcpu)) {
+		vcpu->arch.has_run_once = false;
+		return -EPERM;
+	}
 
 	kvm_arm_vcpu_init_debug(vcpu);
 
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 64d51aa3aee3..e34351fdc66c 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1436,6 +1436,10 @@ static int __set_id_reg(struct kvm_vcpu *vcpu,
 	if (val != read_id_reg(vcpu, rd, raz) && !GET_ID_REG_INFO(encoding))
 		return -EINVAL;
 
+	/* Don't allow to change the reg after the first KVM_RUN. */
+	if (vcpu->arch.has_run_once)
+		return -EINVAL;
+
 	if (raz)
 		return 0;
 
@@ -3004,6 +3008,33 @@ int kvm_arm_copy_sys_reg_indices(struct kvm_vcpu *vcpu, u64 __user *uindices)
 	return write_demux_regids(uindices);
 }
 
+int kvm_id_regs_consistency_check(const struct kvm_vcpu *vcpu)
+{
+	int i;
+	const struct kvm_vcpu *t_vcpu;
+
+	/*
+	 * Make sure vcpu->arch.has_run_once is visible for others so that
+	 * ID regs' consistency between two vCPUs is checked by either one
+	 * at least.
+	 */
+	smp_mb();
+	WARN_ON(!vcpu->arch.has_run_once);
+
+	kvm_for_each_vcpu(i, t_vcpu, vcpu->kvm) {
+		if (!t_vcpu->arch.has_run_once)
+			/* ID regs still could be updated. */
+			continue;
+
+		if (memcmp(&__vcpu_sys_reg(vcpu, ID_REG_BASE),
+			   &__vcpu_sys_reg(t_vcpu, ID_REG_BASE),
+			   sizeof(__vcpu_sys_reg(vcpu, ID_REG_BASE)) *
+					KVM_ARM_ID_REG_MAX_NUM))
+			return -EINVAL;
+	}
+	return 0;
+}
+
 static void id_reg_info_init_all(void)
 {
 	int i;
-- 
2.33.1.1089.g2158813163f-goog