Commit abec749f authored by David Hildenbrand's avatar David Hildenbrand Committed by Linus Torvalds
Browse files

fs/proc/page.c: allow inspection of last section and fix end detection 

If max_pfn does not fall onto a section boundary, it is possible to
inspect PFNs up to max_pfn, and PFNs above max_pfn, however, max_pfn
itself can't be inspected.  We can have a valid (and online) memmap at and
above max_pfn if max_pfn is not aligned to a section boundary.  The whole
early section has a memmap and is marked online.  Being able to inspect
the state of these PFNs is valuable for debugging, especially because
max_pfn can change on memory hotplug and expose these memmaps.

Also, querying page flags via "./page-types -r -a 0x144001,"
(tools/vm/page-types.c) inside a x86-64 guest with 4160MB under QEMU
results in an (almost) endless loop in user space, because the end is not
detected properly when starting after max_pfn.

Instead, let's allow to inspect all pages in the highest section and
return 0 directly if we try to access pages above that section.

While at it, check the count before adjusting it, to avoid masking user
errors.

Link: http://lkml.kernel.org/r/20191211163201.17179-3-david@redhat.com


Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Bob Picco <bob.picco@oracle.com>
Cc: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: Steven Sistare <steven.sistare@oracle.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e822969c

fs/proc/page.c

+27 −3
Original line number Diff line number Diff line
@@ -21,6 +21,21 @@ 
#define KPMMASK (KPMSIZE - 1)

#define KPMBITS (KPMSIZE * BITS_PER_BYTE)



static inline unsigned long get_max_dump_pfn(void)

{

#ifdef CONFIG_SPARSEMEM

	/*

	 * The memmap of early sections is completely populated and marked

	 * online even if max_pfn does not fall on a section boundary -

	 * pfn_to_online_page() will succeed on all pages. Allow inspecting

	 * these memmaps.

	 */

	return round_up(max_pfn, PAGES_PER_SECTION);

#else

	return max_pfn;

#endif

}



/* /proc/kpagecount - an array exposing page counts

 *

 * Each entry is a u64 representing the corresponding
@@ -29,6 +44,7 @@ 
static ssize_t kpagecount_read(struct file *file, char __user *buf,

			     size_t count, loff_t *ppos)

{

	const unsigned long max_dump_pfn = get_max_dump_pfn();

	u64 __user *out = (u64 __user *)buf;

	struct page *ppage;

	unsigned long src = *ppos;
@@ -37,9 +53,11 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf, 
	u64 pcount;



	pfn = src / KPMSIZE;

	count = min_t(size_t, count, (max_pfn * KPMSIZE) - src);

	if (src & KPMMASK || count & KPMMASK)

		return -EINVAL;

	if (src >= max_dump_pfn * KPMSIZE)

		return 0;

	count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);



	while (count > 0) {

		/*
@@ -206,6 +224,7 @@ u64 stable_page_flags(struct page *page) 
static ssize_t kpageflags_read(struct file *file, char __user *buf,

			     size_t count, loff_t *ppos)

{

	const unsigned long max_dump_pfn = get_max_dump_pfn();

	u64 __user *out = (u64 __user *)buf;

	struct page *ppage;

	unsigned long src = *ppos;
@@ -213,9 +232,11 @@ static ssize_t kpageflags_read(struct file *file, char __user *buf, 
	ssize_t ret = 0;



	pfn = src / KPMSIZE;

	count = min_t(unsigned long, count, (max_pfn * KPMSIZE) - src);

	if (src & KPMMASK || count & KPMMASK)

		return -EINVAL;

	if (src >= max_dump_pfn * KPMSIZE)

		return 0;

	count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);



	while (count > 0) {

		/*
@@ -251,6 +272,7 @@ static const struct file_operations proc_kpageflags_operations = { 
static ssize_t kpagecgroup_read(struct file *file, char __user *buf,

				size_t count, loff_t *ppos)

{

	const unsigned long max_dump_pfn = get_max_dump_pfn();

	u64 __user *out = (u64 __user *)buf;

	struct page *ppage;

	unsigned long src = *ppos;
@@ -259,9 +281,11 @@ static ssize_t kpagecgroup_read(struct file *file, char __user *buf, 
	u64 ino;



	pfn = src / KPMSIZE;

	count = min_t(unsigned long, count, (max_pfn * KPMSIZE) - src);

	if (src & KPMMASK || count & KPMMASK)

		return -EINVAL;

	if (src >= max_dump_pfn * KPMSIZE)

		return 0;

	count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);



	while (count > 0) {

		/*

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