[PATCH] x86/sgx: Fix deadloop in __sgx_alloc_epc_page()

[Aaron Lu <aaron.lu@intel.com>]

When current node doesn't have a EPC section configured by firmware and
all other EPC sections memory are used up, CPU can stuck inside the
while loop in __sgx_alloc_epc_page() forever and soft lockup will happen.
Note how nid_of_current will never equal to nid in that while loop because
nid_of_current is not set in sgx_numa_mask.

Also worth mentioning is that it's perfectly fine for firmware to not
seup an EPC section on a node. Setting an EPC section on each node can
be good for performance but that's not a requirement functionality wise.

Fixes: 901ddbb9ecf5 ("x86/sgx: Add a basic NUMA allocation scheme to sgx_alloc_epc_page()")
Reported-by: Zhimin Luo <zhimin.luo@intel.com>
Tested-by: Zhimin Luo <zhimin.luo@intel.com>
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
---
This issue is found by Zhimin when doing internal testing and no
external bug report has been sent out so there is no Closes: tag.

 arch/x86/kernel/cpu/sgx/main.c | 27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 1a000acd933a..694fcf7a5e3a 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -475,24 +475,25 @@ struct sgx_epc_page *__sgx_alloc_epc_page(void)
 {
 	struct sgx_epc_page *page;
 	int nid_of_current = numa_node_id();
-	int nid = nid_of_current;
+	int nid_start, nid;
 
-	if (node_isset(nid_of_current, sgx_numa_mask)) {
-		page = __sgx_alloc_epc_page_from_node(nid_of_current);
-		if (page)
-			return page;
-	}
-
-	/* Fall back to the non-local NUMA nodes: */
-	while (true) {
-		nid = next_node_in(nid, sgx_numa_mask);
-		if (nid == nid_of_current)
-			break;
+	/*
+	 * Try local node first. If it doesn't have an EPC section,
+	 * fall back to the non-local NUMA nodes.
+	 */
+	if (node_isset(nid_of_current, sgx_numa_mask))
+		nid_start = nid_of_current;
+	else
+		nid_start = next_node_in(nid_of_current, sgx_numa_mask);
 
+	nid = nid_start;
+	do {
 		page = __sgx_alloc_epc_page_from_node(nid);
 		if (page)
 			return page;
-	}
+
+		nid = next_node_in(nid, sgx_numa_mask);
+	} while (nid != nid_start);
 
 	return ERR_PTR(-ENOMEM);
 }

base-commit: a85536e1bce722cb184abbac98068217874bdd6e
-- 
2.45.2