[PATCH v6 33/38] KVM: arm64: Introduce KVM_PGTABLE_S2_IDMAP stage 2 flag

[Quentin Perret]

Introduce a new stage 2 configuration flag to specify that all mappings
in a given page-table will be identity-mapped, as will be the case for
the host. This allows to introduce sanity checks in the map path and to
avoid programming errors.

Suggested-by: Will Deacon <will at kernel.org>
Signed-off-by: Quentin Perret <qperret at google.com>
---
 arch/arm64/include/asm/kvm_pgtable.h | 2 ++
 arch/arm64/kvm/hyp/pgtable.c         | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/arch/arm64/include/asm/kvm_pgtable.h b/arch/arm64/include/asm/kvm_pgtable.h
index 55452f4831d2..c3674c47d48c 100644
--- a/arch/arm64/include/asm/kvm_pgtable.h
+++ b/arch/arm64/include/asm/kvm_pgtable.h
@@ -60,9 +60,11 @@ struct kvm_pgtable_mm_ops {
  * enum kvm_pgtable_stage2_flags - Stage-2 page-table flags.
  * @KVM_PGTABLE_S2_NOFWB:	Don't enforce Normal-WB even if the CPUs have
  *				ARM64_HAS_STAGE2_FWB.
+ * @KVM_PGTABLE_S2_IDMAP:	Only use identity mappings.
  */
 enum kvm_pgtable_stage2_flags {
 	KVM_PGTABLE_S2_NOFWB			= BIT(0),
+	KVM_PGTABLE_S2_IDMAP			= BIT(1),
 };
 
 /**
diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index b22b4860630c..c37c1dc4feaf 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -760,6 +760,9 @@ int kvm_pgtable_stage2_map(struct kvm_pgtable *pgt, u64 addr, u64 size,
 		.arg		= &map_data,
 	};
 
+	if (WARN_ON((pgt->flags & KVM_PGTABLE_S2_IDMAP) && (addr != phys)))
+		return -EINVAL;
+
 	ret = stage2_set_prot_attr(pgt, prot, &map_data.attr);
 	if (ret)
 		return ret;
-- 
2.31.0.rc2.261.g7f71774620-goog