Commit 0709682c authored by Guilherme G. Piccoli's avatar Guilherme G. Piccoli Committed by Mike Rapoport (Microsoft)
Browse files

memblock: Add reserve_mem debugfs info 

When using the "reserve_mem" parameter, users aim at having an
area that (hopefully) persists across boots, so pstore infrastructure
(like ramoops module) can make use of that to save oops/ftrace logs,
for example.

There is no easy way to determine if this kernel parameter is properly
set though; the kernel doesn't show information about this memory in
memblock debugfs, neither in /proc/iomem nor dmesg. This is a relevant
information for tools like kdumpst[0], to determine if it's reliable
to use the reserved area as ramoops persistent storage; checking only
/proc/cmdline is not sufficient as it doesn't tell if the reservation
effectively succeeded or not.

Add here a new file under memblock debugfs showing properly set memory
reservations, with name and size as passed to "reserve_mem". Notice that
if no "reserve_mem=" is passed on command-line or if the reservation
attempts fail, the file is not created.

[0] https://aur.archlinux.org/packages/kdumpst



Reviewed-by: default avatarSeongJae Park <sj@kernel.org>
Signed-off-by: default avatarGuilherme G. Piccoli <gpiccoli@igalia.com>
Link: https://patch.msgid.link/20260324012839.1991765-2-gpiccoli@igalia.com


Signed-off-by: default avatarMike Rapoport (Microsoft) <rppt@kernel.org>
parent f7f4a21c

mm/memblock.c

+45 −4
Original line number Diff line number Diff line
@@ -17,6 +17,7 @@ 
#include <linux/seq_file.h>

#include <linux/memblock.h>

#include <linux/mutex.h>

#include <linux/string_helpers.h>



#ifdef CONFIG_KEXEC_HANDOVER

#include <linux/libfdt.h>
@@ -2710,7 +2711,8 @@ static int __init reserve_mem(char *p) 
}

__setup("reserve_mem=", reserve_mem);



#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_ARCH_KEEP_MEMBLOCK)

#ifdef CONFIG_DEBUG_FS

#ifdef CONFIG_ARCH_KEEP_MEMBLOCK

static const char * const flagname[] = {

	[ilog2(MEMBLOCK_HOTPLUG)] = "HOTPLUG",

	[ilog2(MEMBLOCK_MIRROR)] = "MIRROR",
@@ -2757,10 +2759,8 @@ static int memblock_debug_show(struct seq_file *m, void *private) 
}

DEFINE_SHOW_ATTRIBUTE(memblock_debug);



static int __init memblock_init_debugfs(void)

static inline void memblock_debugfs_expose_arrays(struct dentry *root)

{

	struct dentry *root = debugfs_create_dir("memblock", NULL);



	debugfs_create_file("memory", 0444, root,

			    &memblock.memory, &memblock_debug_fops);

	debugfs_create_file("reserved", 0444, root,
@@ -2769,7 +2769,48 @@ static int __init memblock_init_debugfs(void) 
	debugfs_create_file("physmem", 0444, root, &physmem,

			    &memblock_debug_fops);

#endif

}



#else



static inline void memblock_debugfs_expose_arrays(struct dentry *root) { }



#endif /* CONFIG_ARCH_KEEP_MEMBLOCK */



static int memblock_reserve_mem_show(struct seq_file *m, void *private)

{

	struct reserve_mem_table *map;

	char txtsz[16];



	guard(mutex)(&reserve_mem_lock);

	for (int i = 0; i < reserved_mem_count; i++) {

		map = &reserved_mem_table[i];

		if (!map->size)

			continue;



		memset(txtsz, 0, sizeof(txtsz));

		string_get_size(map->size, 1, STRING_UNITS_2, txtsz, sizeof(txtsz));

		seq_printf(m, "%s\t\t(%s)\n", map->name, txtsz);

	}



	return 0;

}

DEFINE_SHOW_ATTRIBUTE(memblock_reserve_mem);



static int __init memblock_init_debugfs(void)

{

	struct dentry *root;



	if (!IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK) && !reserved_mem_count)

		return 0;



	root = debugfs_create_dir("memblock", NULL);



	if (reserved_mem_count)

		debugfs_create_file("reserve_mem_param", 0444, root, NULL,

				    &memblock_reserve_mem_fops);



	memblock_debugfs_expose_arrays(root);

	return 0;

}

__initcall(memblock_init_debugfs);

tools/testing/memblock/linux/string_helpers.h

0 → 100644
+10 −0
Original line number Diff line number Diff line 
/* SPDX-License-Identifier: GPL-2.0 */

#ifndef _LINUX_STRING_HELPERS_H_

#define _LINUX_STRING_HELPERS_H_



/*

 * Header stub to avoid test build breakage; we don't need to

 * actually implement string_get_size() as it's not used in the tests.

 */



#endif