kvm: x86/mmu: Allocate and free TDP MMU roots

The TDP MMU must be able to allocate paging structure root pages and track
the usage of those pages. Implement a similar, but separate system for root
page allocation to that of the x86 shadow paging implementation. When
future patches add synchronization model changes to allow for parallel
page faults, these pages will need to be handled differently from the
x86 shadow paging based MMU's root pages.

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>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index fc72f199eaa6..6665b10288ce 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -55,8 +55,12 @@ struct kvm_mmu_page {
 
 	/* Number of writes since the last time traversal visited this page.  */
 	atomic_t write_flooding_count;
+
+	bool tdp_mmu_page;
 };
 
+extern struct kmem_cache *mmu_page_header_cache;
+
 static inline struct kvm_mmu_page *to_shadow_page(hpa_t shadow_page)
 {
 	struct page *page = pfn_to_page(shadow_page >> PAGE_SHIFT);
@@ -89,4 +93,20 @@ void kvm_mmu_gfn_allow_lpage(struct kvm_memory_slot *slot, gfn_t gfn);
 bool kvm_mmu_slot_gfn_write_protect(struct kvm *kvm,
 				    struct kvm_memory_slot *slot, u64 gfn);
 
+static inline void kvm_mmu_get_root(struct kvm *kvm, struct kvm_mmu_page *sp)
+{
+	BUG_ON(!sp->root_count);
+	lockdep_assert_held(&kvm->mmu_lock);
+
+	++sp->root_count;
+}
+
+static inline bool kvm_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *sp)
+{
+	lockdep_assert_held(&kvm->mmu_lock);
+	--sp->root_count;
+
+	return !sp->root_count;
+}
+
 #endif /* __KVM_X86_MMU_INTERNAL_H */