[RFC PATCH 21/42] iommu/vt-d: Check reserved bits for IOMMU_DOMAIN_KVM domain

[Yan Zhao]

Compatibility check between IOMMU driver and KVM.
rsvd_bits_mask is provided by KVM to guarantee that the set bits are
must-be-zero bits in PTEs. Intel vt-d driver can check it to see if all
must-be-zero bits required by IOMMU side are included.

In this RFC, only bit 11 is checked for simplicity and demo purpose.

Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
---
 drivers/iommu/intel/kvm.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/iommu/intel/kvm.c b/drivers/iommu/intel/kvm.c
index 1ce334785430b..998d6daaf7ea1 100644
--- a/drivers/iommu/intel/kvm.c
+++ b/drivers/iommu/intel/kvm.c
@@ -32,6 +32,18 @@ static bool is_iommu_cap_compatible_to_kvm_domain(struct dmar_domain *domain,
 	return true;
 }
 
+static int check_tdp_reserved_bits(const struct kvm_exported_tdp_meta_vmx *tdp)
+{
+	int i;
+
+	for (i = PT64_ROOT_MAX_LEVEL; --i >= 0;) {
+		if (!(tdp->rsvd_bits_mask[0][i] & BIT(11)) ||
+		    !(tdp->rsvd_bits_mask[1][i] & BIT(11)))
+			return -EFAULT;
+	}
+	return 0;
+}
+
 int prepare_kvm_domain_attach(struct dmar_domain *domain, struct intel_iommu *iommu)
 {
 	if (is_iommu_cap_compatible_to_kvm_domain(domain, iommu))
@@ -90,6 +102,11 @@ intel_iommu_domain_alloc_kvm(struct device *dev, u32 flags, const void *data)
 		return ERR_PTR(-EOPNOTSUPP);
 	}
 
+	if (check_tdp_reserved_bits(tdp)) {
+		pr_err("Reserved bits incompatible between KVM and IOMMU\n");
+		return ERR_PTR(-EOPNOTSUPP);
+	}
+
 	dmar_domain = alloc_domain(IOMMU_DOMAIN_KVM);
 	if (!dmar_domain)
 		return ERR_PTR(-ENOMEM);
-- 
2.17.1