mm: introduce execmem_alloc() and execmem_free()

module_alloc() is used everywhere as a mean to allocate memory for code.

Beside being semantically wrong, this unnecessarily ties all subsystems
that need to allocate code, such as ftrace, kprobes and BPF to modules and
puts the burden of code allocation to the modules code.

Several architectures override module_alloc() because of various
constraints where the executable memory can be located and this causes
additional obstacles for improvements of code allocation.

Start splitting code allocation from modules by introducing execmem_alloc()
and execmem_free() APIs.

Initially, execmem_alloc() is a wrapper for module_alloc() and
execmem_free() is a replacement of module_memfree() to allow updating all
call sites to use the new APIs.

Since architectures define different restrictions on placement,
permissions, alignment and other parameters for memory that can be used by
different subsystems that allocate executable memory, execmem_alloc() takes
a type argument, that will be used to identify the calling subsystem and to
allow architectures define parameters for ranges suitable for that
subsystem.

No functional changes.

Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

3 files changed, 36 insertions, 0 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index f30a18a0e37d..8bb60fdaba3c 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -1240,6 +1240,9 @@ config LOCK_MM_AND_FIND_VMA
 config IOMMU_MM_DATA
 	bool
 
+config EXECMEM
+	bool
+
 source "mm/damon/Kconfig"
 
 endmenu
diff --git a/mm/Makefile b/mm/Makefile
index 4abb40b911ec..001336c91864 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -133,3 +133,4 @@ obj-$(CONFIG_IO_MAPPING) += io-mapping.o
 obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o
 obj-$(CONFIG_GENERIC_IOREMAP) += ioremap.o
 obj-$(CONFIG_SHRINKER_DEBUG) += shrinker_debug.o
+obj-$(CONFIG_EXECMEM) += execmem.o
diff --git a/mm/execmem.c b/mm/execmem.c
new file mode 100644
index 000000000000..480adc69b20d
--- /dev/null
+++ b/mm/execmem.c
@@ -0,0 +1,32 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2002 Richard Henderson
+ * Copyright (C) 2001 Rusty Russell, 2002, 2010 Rusty Russell IBM.
+ * Copyright (C) 2023 Luis Chamberlain <mcgrof@kernel.org>
+ * Copyright (C) 2024 Mike Rapoport IBM.
+ */
+
+#include <linux/mm.h>
+#include <linux/vmalloc.h>
+#include <linux/execmem.h>
+#include <linux/moduleloader.h>
+
+static void *__execmem_alloc(size_t size)
+{
+	return module_alloc(size);
+}
+
+void *execmem_alloc(enum execmem_type type, size_t size)
+{
+	return __execmem_alloc(size);
+}
+
+void execmem_free(void *ptr)
+{
+	/*
+	 * This memory may be RO, and freeing RO memory in an interrupt is not
+	 * supported by vmalloc.
+	 */
+	WARN_ON(in_interrupt());
+	vfree(ptr);
+}