KVM: VMX: Let the compiler save/load RDX during vCPU-run

Per commit c2036300 ("KVM: VMX: Let gcc to choose which registers
to save (x86_64)"), the only reason RDX is saved/loaded to/from the
stack is because it was specified as an input, i.e. couldn't be marked
as clobbered (ignoring the fact that "saving" it to a dummy output
would indirectly mark it as clobbered).

Now that RDX is no longer an input, clobber it.
Reviewed-by: NJim Mattson <jmattson@google.com>
Signed-off-by: NSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/vmx.c

@@ -6377,7 +6377,7 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
 
 	asm(
 		/* Store host registers */
-		"push %%" _ASM_DX "; push %%" _ASM_BP ";"
+		"push %%" _ASM_BP " \n\t"
 		"sub $%c[wordsize], %%" _ASM_SP "\n\t" /* placeholder for guest RCX */
 		"push %%" _ASM_CX " \n\t"
 		"sub $%c[wordsize], %%" _ASM_SP "\n\t" /* temporarily adjust RSP for CALL */
@@ -6481,7 +6481,7 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
 		"xor %%esi, %%esi \n\t"
 		"xor %%edi, %%edi \n\t"
 		"xor %%ebp, %%ebp \n\t"
-		"pop  %%" _ASM_BP "; pop  %%" _ASM_DX " \n\t"
+		"pop  %%" _ASM_BP " \n\t"
 	      : ASM_CALL_CONSTRAINT, "=S"((int){0})
 	      : "c"(vmx), "S"(evmcs_rsp),
 		[launched]"i"(offsetof(struct vcpu_vmx, __launched)),
@@ -6509,10 +6509,10 @@ static void __vmx_vcpu_run(struct kvm_vcpu *vcpu, struct vcpu_vmx *vmx)
 		[wordsize]"i"(sizeof(ulong))
 	      : "cc", "memory"
 #ifdef CONFIG_X86_64
-		, "rax", "rbx", "rdi"
+		, "rax", "rbx", "rdx", "rdi"
 		, "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15"
 #else
-		, "eax", "ebx", "edi"
+		, "eax", "ebx", "edx", "edi"
 #endif
 	      );
 }