x86/sgx: Make sgx_ipi_cb() available internally

The ETRACK function followed by an IPI to all CPUs within an enclave
is a common pattern with more frequent use in support of SGX2.

Make the (empty) IPI callback function available internally in
preparation for usage by SGX2.
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lkml.kernel.org/r/1179ed4a9c3c1c2abf49d51bfcf2c30b493181cc.1652137848.git.reinette.chatre@intel.com

arch/x86/kernel/cpu/sgx/main.c

@@ -174,7 +174,7 @@ static int __sgx_encl_ewb(struct sgx_epc_page *epc_page, void *va_slot,
 	return ret;
 }
 
-static void sgx_ipi_cb(void *info)
+void sgx_ipi_cb(void *info)
 {
 }
 

arch/x86/kernel/cpu/sgx/sgx.h

@@ -90,6 +90,8 @@ void sgx_mark_page_reclaimable(struct sgx_epc_page *page);
 int sgx_unmark_page_reclaimable(struct sgx_epc_page *page);
 struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim);
 
+void sgx_ipi_cb(void *info);
+
 #ifdef CONFIG_X86_SGX_KVM
 int __init sgx_vepc_init(void);
 #else