KVM: x86: SVM: Set EMULTYPE_NO_REEXECUTE for RSM emulation

Re-execution after an emulation decode failure is only intended to
handle a case where two or vCPUs race to write a shadowed page, i.e.
we should never re-execute an instruction as part of RSM emulation.

Add a new helper, kvm_emulate_instruction_from_buffer(), to support
emulating from a pre-defined buffer.  This eliminates the last direct
call to x86_emulate_instruction() outside of kvm_mmu_page_fault(),
which means x86_emulate_instruction() can be unexported in a future
patch.

Fixes: 7607b717 ("KVM: SVM: install RSM intercept")
Cc: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -1251,6 +1251,13 @@ static inline int emulate_instruction(struct kvm_vcpu *vcpu,
 			emulation_type | EMULTYPE_NO_REEXECUTE, NULL, 0);
 }
 
+static inline int kvm_emulate_instruction_from_buffer(struct kvm_vcpu *vcpu,
+						      void *insn, int insn_len)
+{
+	return x86_emulate_instruction(vcpu, 0, EMULTYPE_NO_REEXECUTE,
+				       insn, insn_len);
+}
+
 void kvm_enable_efer_bits(u64);
 bool kvm_valid_efer(struct kvm_vcpu *vcpu, u64 efer);
 int kvm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr);

arch/x86/kvm/svm.c

@@ -3874,7 +3874,7 @@ static int emulate_on_interception(struct vcpu_svm *svm)
 
 static int rsm_interception(struct vcpu_svm *svm)
 {
-	return x86_emulate_instruction(&svm->vcpu, 0, 0,
+	return kvm_emulate_instruction_from_buffer(&svm->vcpu,
 					rsm_ins_bytes, 2) == EMULATE_DONE;
 }