Linux 5.8 compat: __vmalloc()

The `pgprot` argument has been removed from `__vmalloc` in Linux 5.8,
being `PAGE_KERNEL` always now [1].

Detect this during configure and define a wrapper for older kernels.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/mm/vmalloc.c?h=next-20200605&id=88dca4ca5a93d2c09e5bbc6a62fbfc3af83c4fca

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Sebastian Gottschall <s.gottschall@dd-wrt.com>
Co-authored-by: Michael Niewöhner <foss@mniewoehner.de>
Signed-off-by: Sebastian Gottschall <s.gottschall@dd-wrt.com>
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Closes openzfs#10422

(cherry picked from commit 080102a)
- apply to 0.8.4 before certain files were moved around
- config/kernel-kmem.m4 exists in git but not release tarballs because
  it is unused; introduce it in a new file to prevent conflicts
- linux/mm.h is included in git master via sys/kmem.h; do not remove it
  here or the build will error due to undefined is_vmalloc_addr()

Original-patch-by: Michael Niewöhner <c0d3z3r0@users.noreply.github.com>
Signed-off-by: Eli Schwartz <eschwartz@archlinux.org>

config/kernel-kmem-vmalloc.m4

@@ -0,0 +1,24 @@
+dnl #
+dnl # 5.8 API,
+dnl # __vmalloc PAGE_KERNEL removal
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SRC_VMALLOC_PAGE_KERNEL], [
+	ZFS_LINUX_TEST_SRC([__vmalloc], [
+		#include <linux/mm.h>
+		#include <linux/vmalloc.h>
+	],[
+		void *p __attribute__ ((unused));
+
+		p = __vmalloc(0, GFP_KERNEL, PAGE_KERNEL);
+	])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_VMALLOC_PAGE_KERNEL], [
+	AC_MSG_CHECKING([whether __vmalloc(ptr, flags, pageflags) is available])
+	ZFS_LINUX_TEST_RESULT([__vmalloc], [
+		AC_MSG_RESULT(yes)
+		AC_DEFINE(HAVE_VMALLOC_PAGE_KERNEL, 1, [__vmalloc page flags exists])
+	],[
+		AC_MSG_RESULT(no)
+	])
+])

config/kernel.m4

@@ -45,6 +45,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_SRC], [
 	ZFS_AC_KERNEL_SRC_SCHED
 	ZFS_AC_KERNEL_SRC_USLEEP_RANGE
 	ZFS_AC_KERNEL_SRC_KMEM_CACHE
+	ZFS_AC_KERNEL_SRC_VMALLOC_PAGE_KERNEL
 	ZFS_AC_KERNEL_SRC_WAIT
 	ZFS_AC_KERNEL_SRC_INODE_TIMES
 	ZFS_AC_KERNEL_SRC_INODE_LOCK
@@ -163,6 +164,7 @@ AC_DEFUN([ZFS_AC_KERNEL_TEST_RESULT], [
 	ZFS_AC_KERNEL_SCHED
 	ZFS_AC_KERNEL_USLEEP_RANGE
 	ZFS_AC_KERNEL_KMEM_CACHE
+	ZFS_AC_KERNEL_VMALLOC_PAGE_KERNEL
 	ZFS_AC_KERNEL_WAIT
 	ZFS_AC_KERNEL_INODE_TIMES
 	ZFS_AC_KERNEL_INODE_LOCK

include/spl/sys/kmem.h

@@ -169,6 +169,15 @@ extern void *spl_kmem_alloc(size_t sz, int fl, const char *func, int line);
 extern void *spl_kmem_zalloc(size_t sz, int fl, const char *func, int line);
 extern void spl_kmem_free(const void *ptr, size_t sz);
 
+/*
+ * 5.8 API change, pgprot_t argument removed.
+ */
+#ifdef HAVE_VMALLOC_PAGE_KERNEL
+#define	spl_vmalloc(size, flags)	__vmalloc(size, flags, PAGE_KERNEL)
+#else
+#define	spl_vmalloc(size, flags)	__vmalloc(size, flags)
+#endif
+
 /*
  * The following functions are only available for internal use.
  */

module/spl/spl-kmem-cache.c

@@ -203,7 +203,7 @@ kv_alloc(spl_kmem_cache_t *skc, int size, int flags)
 		ASSERT(ISP2(size));
 		ptr = (void *)__get_free_pages(lflags, get_order(size));
 	} else {
-		ptr = __vmalloc(size, lflags | __GFP_HIGHMEM, PAGE_KERNEL);
+		ptr = spl_vmalloc(size, lflags | __GFP_HIGHMEM);
 	}
 
 	/* Resulting allocated memory will be page aligned */
@@ -1242,7 +1242,7 @@ spl_cache_grow(spl_kmem_cache_t *skc, int flags, void **obj)
 	 * allocation.
 	 *
 	 * However, this can't be applied to KVM_VMEM due to a bug that
-	 * __vmalloc() doesn't honor gfp flags in page table allocation.
+	 * spl_vmalloc() doesn't honor gfp flags in page table allocation.
 	 */
 	if (!(skc->skc_flags & KMC_VMEM)) {
 		rc = __spl_cache_grow(skc, flags | KM_NOSLEEP);

module/spl/spl-kmem.c

@@ -172,16 +172,15 @@ spl_kmem_alloc_impl(size_t size, int flags, int node)
 		 * kmem_zalloc() callers.
 		 *
 		 * For vmem_alloc() and vmem_zalloc() callers it is permissible
-		 * to use __vmalloc().  However, in general use of __vmalloc()
-		 * is strongly discouraged because a global lock must be
-		 * acquired.  Contention on this lock can significantly
+		 * to use spl_vmalloc().  However, in general use of
+		 * spl_vmalloc() is strongly discouraged because a global lock
+		 * must be acquired.  Contention on this lock can significantly
 		 * impact performance so frequently manipulating the virtual
 		 * address space is strongly discouraged.
 		 */
 		if ((size > spl_kmem_alloc_max) || use_vmem) {
 			if (flags & KM_VMEM) {
-				ptr = __vmalloc(size, lflags | __GFP_HIGHMEM,
-				    PAGE_KERNEL);
+				ptr = spl_vmalloc(size, lflags | __GFP_HIGHMEM);
 			} else {
 				return (NULL);
 			}