[PATCH 1/2] KVM: arm64: mixed-width check should be skipped for uninitialized vCPUs

[Reiji Watanabe]

vcpu_allowed_register_width() checks if all the VCPUs are either
all 32bit or all 64bit.  Since the checking is done even for vCPUs
that are not initialized (KVM_ARM_VCPU_INIT has not been done) yet,
the non-initialized vCPUs are erroneously treated as 64bit vCPU,
which causes the function to incorrectly detect a mixed-width VM.

Fix vcpu_allowed_register_width() to skip the check for vCPUs that
are not initialized yet.

Fixes: 66e94d5cafd4 ("KVM: arm64: Prevent mixed-width VM creation")
Signed-off-by: Reiji Watanabe <reijiw at google.com>
---
 arch/arm64/kvm/reset.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
index 426bd7fbc3fd..ef78bbc7566a 100644
--- a/arch/arm64/kvm/reset.c
+++ b/arch/arm64/kvm/reset.c
@@ -180,8 +180,19 @@ static bool vcpu_allowed_register_width(struct kvm_vcpu *vcpu)
 	if (kvm_has_mte(vcpu->kvm) && is32bit)
 		return false;
 
+	/*
+	 * Make sure vcpu->arch.target setting is visible from others so
+	 * that the width consistency checking between two vCPUs is done
+	 * by at least one of them at KVM_ARM_VCPU_INIT.
+	 */
+	smp_mb();
+
 	/* Check that the vcpus are either all 32bit or all 64bit */
 	kvm_for_each_vcpu(i, tmp, vcpu->kvm) {
+		/* Skip if KVM_ARM_VCPU_INIT is not done for the vcpu yet */
+		if (tmp->arch.target == -1)
+			continue;
+
 		if (vcpu_has_feature(tmp, KVM_ARM_VCPU_EL1_32BIT) != is32bit)
 			return false;
 	}

base-commit: df0cc57e057f18e44dac8e6c18aba47ab53202f9
-- 
2.34.1.575.g55b058a8bb-goog