KVM: x86/mmu: Use MMU role_regs to get LA57, and drop vCPU LA57 helper

Get LA57 from the role_regs, which are initialized from the vCPU even
though TDP is enabled, instead of pulling the value directly from the
vCPU when computing the guest's root_level for TDP MMUs.  Note, the check
is inside an is_long_mode() statement, so that requirement is not lost.

Use role_regs even though the MMU's role is available and arguably
"better".  A future commit will consolidate the guest root level logic,
and it needs access to EFER.LMA, which is not tracked in the role (it
can't be toggled on VM-Exit, unlike LA57).

Drop is_la57_mode() as there are no remaining users, and to discourage
pulling MMU state from the vCPU (in the future).

No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210622175739.3610207-41-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

@@ -4635,7 +4635,7 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
 		context->gva_to_gpa = nonpaging_gva_to_gpa;
 		context->root_level = 0;
 	} else if (is_long_mode(vcpu)) {
-		context->root_level = is_la57_mode(vcpu) ?
+		context->root_level = ____is_cr4_la57(&regs) ?
 				PT64_ROOT_5LEVEL : PT64_ROOT_4LEVEL;
 		reset_rsvds_bits_mask(vcpu, context);
 		context->gva_to_gpa = paging64_gva_to_gpa;

arch/x86/kvm/x86.h

@@ -157,16 +157,6 @@ static inline bool is_64_bit_mode(struct kvm_vcpu *vcpu)
 	return cs_l;
 }
 
-static inline bool is_la57_mode(struct kvm_vcpu *vcpu)
-{
-#ifdef CONFIG_X86_64
-	return (vcpu->arch.efer & EFER_LMA) &&
-		 kvm_read_cr4_bits(vcpu, X86_CR4_LA57);
-#else
-	return 0;
-#endif
-}
-
 static inline bool x86_exception_has_error_code(unsigned int vector)
 {
 	static u32 exception_has_error_code = BIT(DF_VECTOR) | BIT(TS_VECTOR) |