[RFC PATCH 20/37] KVM: x86/mmu: Abstract away computing the max mapping level

[David Matlack]

Abstract away kvm_mmu_max_mapping_level(), which is an x86-specific
function for computing the max level that a given GFN can be mapped in
KVM's page tables. This will be used in a future commit to enable moving
the TDP MMU to common code.

Provide a default implementation for non-x86 architectures that just
returns the max level. This will result in more zapping than necessary
when disabling dirty logging (i.e. less than optimal performance) but no
correctness issues.

Signed-off-by: David Matlack <dmatlack at google.com>
---
 arch/x86/kvm/mmu/tdp_mmu.c     | 14 ++++++++++----
 arch/x86/kvm/mmu/tdp_pgtable.c |  7 +++++++
 2 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 7670fbd8e72d..24d1dbd0a1ec 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1696,6 +1696,13 @@ void kvm_tdp_mmu_clear_dirty_pt_masked(struct kvm *kvm,
 		clear_dirty_pt_masked(kvm, root, gfn, mask, wrprot);
 }
 
+__weak int tdp_mmu_max_mapping_level(struct kvm *kvm,
+				     const struct kvm_memory_slot *slot,
+				     struct tdp_iter *iter)
+{
+	return TDP_MAX_HUGEPAGE_LEVEL;
+}
+
 static void zap_collapsible_spte_range(struct kvm *kvm,
 				       struct kvm_mmu_page *root,
 				       const struct kvm_memory_slot *slot)
@@ -1727,15 +1734,14 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
 		/*
 		 * If iter.gfn resides outside of the slot, i.e. the page for
 		 * the current level overlaps but is not contained by the slot,
-		 * then the SPTE can't be made huge.  More importantly, trying
-		 * to query that info from slot->arch.lpage_info will cause an
+		 * then the SPTE can't be made huge. On x86, trying to query
+		 * that info from slot->arch.lpage_info will cause an
 		 * out-of-bounds access.
 		 */
 		if (iter.gfn < start || iter.gfn >= end)
 			continue;
 
-		max_mapping_level = kvm_mmu_max_mapping_level(kvm, slot,
-							      iter.gfn, PG_LEVEL_NUM);
+		max_mapping_level = tdp_mmu_max_mapping_level(kvm, slot, &iter);
 		if (max_mapping_level < iter.level)
 			continue;
 
diff --git a/arch/x86/kvm/mmu/tdp_pgtable.c b/arch/x86/kvm/mmu/tdp_pgtable.c
index b07ed99b4ab1..840d063c45b8 100644
--- a/arch/x86/kvm/mmu/tdp_pgtable.c
+++ b/arch/x86/kvm/mmu/tdp_pgtable.c
@@ -163,3 +163,10 @@ void tdp_mmu_arch_unlink_sp(struct kvm *kvm, struct kvm_mmu_page *sp,
 	if (shared)
 		spin_unlock(&kvm->arch.tdp_mmu_pages_lock);
 }
+
+int tdp_mmu_max_mapping_level(struct kvm *kvm,
+			      const struct kvm_memory_slot *slot,
+			      struct tdp_iter *iter)
+{
+	return kvm_mmu_max_mapping_level(kvm, slot, iter->gfn, PG_LEVEL_NUM);
+}
-- 
2.39.0.rc1.256.g54fd8350bd-goog