KVM: VMX: Improve handle_external_interrupt_irqoff inline assembly

Improve handle_external_interrupt_irqoff inline assembly in several ways:
- remove unneeded %c operand modifiers and "$" prefixes
- use %rsp instead of _ASM_SP, since we are in CONFIG_X86_64 part
- use $-16 immediate to align %rsp
- remove unneeded use of __ASM_SIZE macro
- define "ss" named operand only for X86_64

The patch introduces no functional changes.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Message-Id: <20200504155706.2516956-1-ubizjak@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/vmx.c

@@ -6382,13 +6382,13 @@ static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu)
 
 	asm volatile(
 #ifdef CONFIG_X86_64
-		"mov %%" _ASM_SP ", %[sp]\n\t"
-		"and $0xfffffffffffffff0, %%" _ASM_SP "\n\t"
-		"push $%c[ss]\n\t"
+		"mov %%rsp, %[sp]\n\t"
+		"and $-16, %%rsp\n\t"
+		"push %[ss]\n\t"
 		"push %[sp]\n\t"
 #endif
 		"pushf\n\t"
-		__ASM_SIZE(push) " $%c[cs]\n\t"
+		"push %[cs]\n\t"
 		CALL_NOSPEC
 		:
 #ifdef CONFIG_X86_64
@@ -6397,7 +6397,9 @@ static void handle_external_interrupt_irqoff(struct kvm_vcpu *vcpu)
 		ASM_CALL_CONSTRAINT
 		:
 		[thunk_target]"r"(entry),
+#ifdef CONFIG_X86_64
 		[ss]"i"(__KERNEL_DS),
+#endif
 		[cs]"i"(__KERNEL_CS)
 	);