[RFC PATCH v3 10/10] x86/sgx: Call ENCLS[EUPDATESVN] during SGX initialization

[Cathy Zhang <cathy.zhang@intel.com>]

A snapshot of the processor microcode SVN is taken each boot cycle at
the time when Intel SGX is first used. This results in microcode
updates being loadable at any time, fixing microcode issues. However,
if system boot up through kexec() from error recovery, no hardware
reset happens, any SGX leaf execution during boot up is not assumed
as the first use in such case, and no snapshot of SVN is taken. So,
it's necessary to call ENCLS[EUPDATESVN] to update SVN automatically,
rather than waiting for the admin to do it when he/she is even not
aware of that.

Call ENCLS[EUPDATESVN] after sanitizing pages will increase the chance
of success, for it requires that EPC is empty.

Signed-off-by: Cathy Zhang <cathy.zhang@intel.com>

---
Changes since v1:
 - Update accordingly for update_cpusvn_intel() return *void*.
---
 arch/x86/kernel/cpu/sgx/main.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 20800c543110..48eb10f6c6fc 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -426,6 +426,7 @@ static bool sgx_should_reclaim(unsigned long watermark)
 	       !list_empty(&sgx_active_page_list);
 }
 
+void update_cpusvn_intel(void);
 static int ksgxd(void *p)
 {
 	int srcu_idx;
@@ -440,7 +441,14 @@ static int ksgxd(void *p)
 	__sgx_sanitize_pages(&sgx_dirty_page_list);
 
 	/* sanity check: */
-	WARN_ON(!list_empty(&sgx_dirty_page_list));
+	if (!WARN_ON(!list_empty(&sgx_dirty_page_list))) {
+		/*
+		 * Do SVN update for kexec(). It should complete without error, for
+		 * all EPC pages are unused at this point.
+		 */
+		if (cpuid_eax(SGX_CPUID) & SGX_CPUID_EUPDATESVN)
+			update_cpusvn_intel();
+	}
 
 	while (!kthread_should_stop()) {
 		if (try_to_freeze())
-- 
2.17.1