Patch "x86/sgx: Fix deadlock in SGX NUMA node search" has been added to the 6.6-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    x86/sgx: Fix deadlock in SGX NUMA node search

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-sgx-fix-deadlock-in-sgx-numa-node-search.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 5bb81e1fb3a71df99fa8a0858db18a1123a3b750
Author: Aaron Lu <aaron.lu@xxxxxxxxx>
Date:   Thu Sep 5 16:08:54 2024 +0800

    x86/sgx: Fix deadlock in SGX NUMA node search
    
    [ Upstream commit 9c936844010466535bd46ea4ce4656ef17653644 ]
    
    When the current node doesn't have an EPC section configured by firmware
    and all other EPC sections are used up, CPU can get stuck inside the
    while loop that looks for an available EPC page from remote nodes
    indefinitely, leading to a soft lockup. Note how nid_of_current will
    never be 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 the firmware not
    to setup an EPC section on a node. While setting up an EPC section on
    each node can enhance performance, it is not a requirement for
    functionality.
    
    Rework the loop to start and end on *a* node that has SGX memory. This
    avoids the deadlock looking for the current SGX-lacking node to show up
    in the loop when it never will.
    
    Fixes: 901ddbb9ecf5 ("x86/sgx: Add a basic NUMA allocation scheme to sgx_alloc_epc_page()")
    Reported-by: "Molina Sabido, Gerardo" <gerardo.molina.sabido@xxxxxxxxx>
    Signed-off-by: Aaron Lu <aaron.lu@xxxxxxxxx>
    Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
    Reviewed-by: Kai Huang <kai.huang@xxxxxxxxx>
    Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>
    Acked-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
    Tested-by: Zhimin Luo <zhimin.luo@xxxxxxxxx>
    Link: https://lore.kernel.org/all/20240905080855.1699814-2-aaron.lu%40intel.com
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 166692f2d5011..c7f8c3200e8d7 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -474,24 +474,25 @@ 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);
 }