KVM: x86: compile out TDP MMU on 32-bit systems

The TDP MMU assumes that it can do atomic accesses to 64-bit PTEs.
Rather than just disabling it, compile it out completely so that it
is possible to use for example 64-bit xchg.

To limit the number of stubs, wrap all accesses to tdp_mmu_enabled
or tdp_mmu_page with a function.  Calls to all other functions in
tdp_mmu.c are eliminated and do not even reach the linker.

Reviewed-by: Sean Christopherson <seanjc@google.com>
Tested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 28 insertions, 4 deletions

diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
index cbbdbadd1526..b4b65e3699b3 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.h
+++ b/arch/x86/kvm/mmu/tdp_mmu.h
@@ -5,10 +5,6 @@
 
 #include <linux/kvm_host.h>
 
-void kvm_mmu_init_tdp_mmu(struct kvm *kvm);
-void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm);
-
-bool is_tdp_mmu_root(struct kvm *kvm, hpa_t root);
 hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu);
 void kvm_tdp_mmu_free_root(struct kvm *kvm, struct kvm_mmu_page *root);
 
@@ -47,4 +43,32 @@ bool kvm_tdp_mmu_write_protect_gfn(struct kvm *kvm,
 int kvm_tdp_mmu_get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes,
 			 int *root_level);
 
+#ifdef CONFIG_X86_64
+void kvm_mmu_init_tdp_mmu(struct kvm *kvm);
+void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm);
+static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return kvm->arch.tdp_mmu_enabled; }
+static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return sp->tdp_mmu_page; }
+#else
+static inline void kvm_mmu_init_tdp_mmu(struct kvm *kvm) {}
+static inline void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm) {}
+static inline bool is_tdp_mmu_enabled(struct kvm *kvm) { return false; }
+static inline bool is_tdp_mmu_page(struct kvm_mmu_page *sp) { return false; }
+#endif
+
+static inline bool is_tdp_mmu_root(struct kvm *kvm, hpa_t hpa)
+{
+	struct kvm_mmu_page *sp;
+
+	if (!is_tdp_mmu_enabled(kvm))
+		return false;
+	if (WARN_ON(!VALID_PAGE(hpa)))
+		return false;
+
+	sp = to_shadow_page(hpa);
+	if (WARN_ON(!sp))
+		return false;
+
+	return is_tdp_mmu_page(sp) && sp->root_count;
+}
+
 #endif /* __KVM_X86_MMU_TDP_MMU_H */