[PATCH] fix

[Lorenzo Stoakes (ARM)]

---
 arch/x86/kernel/alternative.c | 39 ++++++++++++++++++++++++++++++++---
 1 file changed, 36 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 62936a3bde19..cafcac95e90e 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -6,6 +6,9 @@
 #include <linux/vmalloc.h>
 #include <linux/memory.h>
 #include <linux/execmem.h>
+#include <linux/cleanup.h>
+#include <linux/kgdb.h>
+#include <linux/mmap_lock.h>

 #include <asm/text-patching.h>
 #include <asm/insn.h>
@@ -2543,6 +2546,30 @@ static void text_poke_memset(void *dst, const void *src, size_t len)

 typedef void text_poke_f(void *dst, const void *src, size_t len);

+static void poke_vmalloc_pages(struct page **pages, void *addr,
+			       bool cross_page_boundary)
+{
+	pages[0] = vmalloc_to_page(addr);
+	if (cross_page_boundary)
+		pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
+}
+
+static void poke_vmalloc_pages_safe(struct page **pages, void *addr,
+				    bool cross_page_boundary)
+{
+	/*
+	 * execmem ROX ranges are shared between modules and can be collapsed to
+	 * huge PMD entries, and this collapse can happen concurrently with a
+	 * racing set_memory_rox().
+	 *
+	 * Prevent vmalloc_to_page() from racing by acquiring an init_mm read
+	 * lock which pairs with the init_mm write lock in
+	 * cpa_collapse_large_pages().
+	 */
+	guard(mmap_read_lock)(&init_mm);
+	poke_vmalloc_pages(pages, addr, cross_page_boundary);
+}
+
 static void *__text_poke(text_poke_f func, void *addr, const void *src, size_t len)
 {
 	bool cross_page_boundary = offset_in_page(addr) + len > PAGE_SIZE;
@@ -2560,9 +2587,15 @@ static void *__text_poke(text_poke_f func, void *addr, const void *src, size_t l
 	BUG_ON(!after_bootmem);

 	if (!core_kernel_text((unsigned long)addr)) {
-		pages[0] = vmalloc_to_page(addr);
-		if (cross_page_boundary)
-			pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
+		/*
+		 * If called from kgdb cannot sleep, but all other CPUs stopped
+		 * anyway so safe.
+		 */
+		if (in_dbg_master())
+			poke_vmalloc_pages(pages, addr, cross_page_boundary);
+		else
+			poke_vmalloc_pages_safe(pages, addr,
+						cross_page_boundary);
 	} else {
 		pages[0] = virt_to_page(addr);
 		WARN_ON(!PageReserved(pages[0]));
--
2.55.0