kvm: x86/mmu: Support write protection for nesting in tdp MMU

To support nested virtualization, KVM will sometimes need to write
protect pages which are part of a shadowed paging structure or are not
writable in the shadowed paging structure. Add a function to write
protect GFN mappings for this purpose.

Tested by running kvm-unit-tests and KVM selftests on an Intel Haswell
machine. This series introduced no new failures.

This series can be viewed in Gerrit at:
	https://linux-review.googlesource.com/c/virt/kvm/kvm/+/2538

Signed-off-by: Ben Gardon <bgardon@google.com>
Message-Id: <20201014182700.2888246-18-bgardon@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index cd1be20..4c62ac8 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1299,6 +1299,10 @@ bool kvm_mmu_slot_gfn_write_protect(struct kvm *kvm,
                write_protected |= __rmap_write_protect(kvm, rmap_head, true);
        }
 
+       if (kvm->arch.tdp_mmu_enabled)
+               write_protected |=
+                       kvm_tdp_mmu_write_protect_gfn(kvm, slot, gfn);
+
        return write_protected;
 }
 

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 0f181f3..1491e2f 100644 (file)
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1078,3 +1078,53 @@ void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
                kvm_mmu_put_root(kvm, root);
        }
 }
+
+/*
+ * Removes write access on the last level SPTE mapping this GFN and unsets the
+ * SPTE_MMU_WRITABLE bit to ensure future writes continue to be intercepted.
+ * Returns true if an SPTE was set and a TLB flush is needed.
+ */
+static bool write_protect_gfn(struct kvm *kvm, struct kvm_mmu_page *root,
+                             gfn_t gfn)
+{
+       struct tdp_iter iter;
+       u64 new_spte;
+       bool spte_set = false;
+
+       tdp_root_for_each_leaf_pte(iter, root, gfn, gfn + 1) {
+               if (!is_writable_pte(iter.old_spte))
+                       break;
+
+               new_spte = iter.old_spte &
+                       ~(PT_WRITABLE_MASK | SPTE_MMU_WRITEABLE);
+
+               tdp_mmu_set_spte(kvm, &iter, new_spte);
+               spte_set = true;
+       }
+
+       return spte_set;
+}
+
+/*
+ * Removes write access on the last level SPTE mapping this GFN and unsets the
+ * SPTE_MMU_WRITABLE bit to ensure future writes continue to be intercepted.
+ * Returns true if an SPTE was set and a TLB flush is needed.
+ */
+bool kvm_tdp_mmu_write_protect_gfn(struct kvm *kvm,
+                                  struct kvm_memory_slot *slot, gfn_t gfn)
+{
+       struct kvm_mmu_page *root;
+       int root_as_id;
+       bool spte_set = false;
+
+       lockdep_assert_held(&kvm->mmu_lock);
+       for_each_tdp_mmu_root(kvm, root) {
+               root_as_id = kvm_mmu_page_as_id(root);
+               if (root_as_id != slot->as_id)
+                       continue;
+
+               spte_set |= write_protect_gfn(kvm, root, gfn);
+       }
+       return spte_set;
+}
+

diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index 8cc902b..6501dd2 100644 (file)
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -40,4 +40,7 @@ void kvm_tdp_mmu_clear_dirty_pt_masked(struct kvm *kvm,
 bool kvm_tdp_mmu_slot_set_dirty(struct kvm *kvm, struct kvm_memory_slot *slot);
 void kvm_tdp_mmu_zap_collapsible_sptes(struct kvm *kvm,
                                       const struct kvm_memory_slot *slot);
+
+bool kvm_tdp_mmu_write_protect_gfn(struct kvm *kvm,
+                                  struct kvm_memory_slot *slot, gfn_t gfn);
 #endif /* __KVM_X86_MMU_TDP_MMU_H */