linux-5.15.149 [1] has modified the non-ARCH-specific pfn_valid() to use
__rcu_read_lock/unlock[1] that is marked GPL and cannot be used non open source
nvidia gpu driver builds.

As a workaround, reuse the old implementation of pfn_valid.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/include/linux/mmzone.h?h=v5.15.149&id=b448de2459b6d62a53892487ab18b7d823ff0529
diff --git a/kernel/common/inc/nv-linux.h b/kernel/common/inc/nv-linux.h
index f8df9e3..a5c8634 100644
--- kernel/common/inc/nv-linux.h
+++ kernel/common/inc/nv-linux.h
@@ -2065,2 +2065,23 @@
 
+#if defined(CONFIG_HAVE_ARCH_PFN_VALID) || LINUX_VERSION_CODE < KERNEL_VERSION(5,15,149)
+#  define nv_pfn_valid pfn_valid
+#else
+/* pre-5.15.149 kernel pfn_valid version without GPL rcu_read_lock/unlock() */
+static inline int nv_pfn_valid(unsigned long pfn)
+{
+        struct mem_section *ms;
+
+        if (PHYS_PFN(PFN_PHYS(pfn)) != pfn)
+                return 0;
+
+        if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
+                return 0;
+
+        ms = __pfn_to_section(pfn);
+        if (!valid_section(ms))
+                return 0;
+
+        return early_section(ms) || pfn_section_valid(ms, pfn);
+}
+#endif
 #endif /* _NV_LINUX_H_ */
diff --git a/kernel/nvidia/nv-mmap.c b/kernel/nvidia/nv-mmap.c
index 5926d3c..d2052c4 100644
--- kernel/nvidia/nv-mmap.c
+++ kernel/nvidia/nv-mmap.c
@@ -576,3 +576,3 @@
             if (!IS_REG_OFFSET(nv, access_start, access_len) &&
-                (pfn_valid(PFN_DOWN(mmap_start))))
+                (nv_pfn_valid(PFN_DOWN(mmap_start))))
             {
diff --git a/kernel/nvidia/os-mlock.c b/kernel/nvidia/os-mlock.c
index c97ef4c..44e37c2 100644
--- kernel/nvidia/os-mlock.c
+++ kernel/nvidia/os-mlock.c
@@ -102,3 +102,3 @@
         if ((nv_follow_pfn(vma, (start + (i * PAGE_SIZE)), &pfn) < 0) ||
-            (!pfn_valid(pfn)))
+            (!nv_pfn_valid(pfn)))
         {
@@ -176,3 +176,3 @@
 
-    if (pfn_valid(pfn))
+    if (nv_pfn_valid(pfn))
     {