[PATCH v3 19/19] arm64: text replication: keep modules inside module region when REPLICATE_KTEXT is enabled

[Hao Jia]

Kernel text replication requires maintaining a separate per-node page table
for kernel text. To accomplish this without affecting other kernel memory maps,
it is best to place the kernel in a location that does not share L0 page
table entries with any other mappings.

So, limit the module_alloc() address range so that they do not overlap.

Signed-off-by: Hao Jia <jiahao.os at bytedance.com>
---
 arch/arm64/kernel/module.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/module.c b/arch/arm64/kernel/module.c
index dd851297596e..53e1c5e50907 100644
--- a/arch/arm64/kernel/module.c
+++ b/arch/arm64/kernel/module.c
@@ -112,6 +112,7 @@ subsys_initcall(module_init_limits);
 
 void *module_alloc(unsigned long size)
 {
+	u64 module_direct_end, module_plt_end;
 	void *p = NULL;
 
 	/*
@@ -119,18 +120,33 @@ void *module_alloc(unsigned long size)
 	 * kernel such that no PLTs are necessary.
 	 */
 	if (module_direct_base) {
+#ifdef CONFIG_REPLICATE_KTEXT
+		/*
+		 * Kernel text replication requires an L0 page table entry to
+		 * be exclusive to kernel text, so no other mappings should be
+		 * shared with it.
+		 */
+		module_direct_end = MODULES_END;
+#else
+		module_direct_end = module_direct_base + SZ_128M;
+#endif
 		p = __vmalloc_node_range(size, MODULE_ALIGN,
 					 module_direct_base,
-					 module_direct_base + SZ_128M,
+					 module_direct_end,
 					 GFP_KERNEL | __GFP_NOWARN,
 					 PAGE_KERNEL, 0, NUMA_NO_NODE,
 					 __builtin_return_address(0));
 	}
 
 	if (!p && module_plt_base) {
+#ifdef CONFIG_REPLICATE_KTEXT
+		module_plt_end = MODULES_END;
+#else
+		module_plt_end = module_plt_base + SZ_2G;
+#endif
 		p = __vmalloc_node_range(size, MODULE_ALIGN,
 					 module_plt_base,
-					 module_plt_base + SZ_2G,
+					 module_plt_end,
 					 GFP_KERNEL | __GFP_NOWARN,
 					 PAGE_KERNEL, 0, NUMA_NO_NODE,
 					 __builtin_return_address(0));
-- 
2.20.1