KVM: VMX: Preserve callee-save registers in vCPU-run asm sub-routine

...to make it callable from C code.

Note that because KVM chooses to be ultra paranoid about guest register
values, all callee-save registers are still cleared after VM-Exit even
though the host's values are now reloaded from the stack.
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/vmx/vmenter.S

@@ -92,6 +92,16 @@ ENDPROC(vmx_vmexit)
 ENTRY(__vmx_vcpu_run)
 	push %_ASM_BP
 	mov  %_ASM_SP, %_ASM_BP
+#ifdef CONFIG_X86_64
+	push %r15
+	push %r14
+	push %r13
+	push %r12
+#else
+	push %edi
+	push %esi
+#endif
+	push %_ASM_BX
 
 	/*
 	 * Save @regs, _ASM_ARG2 may be modified by vmx_update_host_rsp() and
@@ -195,6 +205,17 @@ ENTRY(__vmx_vcpu_run)
 
 	/* "POP" @regs. */
 	add $WORD_SIZE, %_ASM_SP
+	pop %_ASM_BX
+
+#ifdef CONFIG_X86_64
+	pop %r12
+	pop %r13
+	pop %r14
+	pop %r15
+#else
+	pop %esi
+	pop %edi
+#endif
 	pop %_ASM_BP
 	ret
 

arch/x86/kvm/vmx/vmx.c

@@ -6456,10 +6456,7 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
 #endif
 	      : "cc", "memory"
 #ifdef CONFIG_X86_64
-		, "rbx", "rcx"
-		, "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15"
-#else
-		, "ebx", "edi", "esi"
+		, "rcx", "r8", "r9", "r10", "r11"
 #endif
 	      );