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Commit 457c1b27 authored by Nishanth Aravamudan's avatar Nishanth Aravamudan Committed by Linus Torvalds
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hugetlb: ensure hugepage access is denied if hugepages are not supported 



Currently, I am seeing the following when I `mount -t hugetlbfs /none
/dev/hugetlbfs`, and then simply do a `ls /dev/hugetlbfs`.  I think it's
related to the fact that hugetlbfs is properly not correctly setting
itself up in this state?:

  Unable to handle kernel paging request for data at address 0x00000031
  Faulting instruction address: 0xc000000000245710
  Oops: Kernel access of bad area, sig: 11 [#1]
  SMP NR_CPUS=2048 NUMA pSeries
  ....

In KVM guests on Power, in a guest not backed by hugepages, we see the
following:

  AnonHugePages:         0 kB
  HugePages_Total:       0
  HugePages_Free:        0
  HugePages_Rsvd:        0
  HugePages_Surp:        0
  Hugepagesize:         64 kB

HPAGE_SHIFT == 0 in this configuration, which indicates that hugepages
are not supported at boot-time, but this is only checked in
hugetlb_init().  Extract the check to a helper function, and use it in a
few relevant places.

This does make hugetlbfs not supported (not registered at all) in this
environment.  I believe this is fine, as there are no valid hugepages
and that won't change at runtime.

[akpm@linux-foundation.org: use pr_info(), per Mel]
[akpm@linux-foundation.org: fix build when HPAGE_SHIFT is undefined]
Signed-off-by: default avatarNishanth Aravamudan <nacc@linux.vnet.ibm.com>
Reviewed-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: default avatarMel Gorman <mgorman@suse.de>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 93030d83

fs/hugetlbfs/inode.c

+5 −0
Original line number Diff line number Diff line
@@ -1030,6 +1030,11 @@ static int __init init_hugetlbfs_fs(void) 
	int error;

	int i;



	if (!hugepages_supported()) {

		pr_info("hugetlbfs: disabling because there are no supported hugepage sizes\n");

		return -ENOTSUPP;

	}



	error = bdi_init(&hugetlbfs_backing_dev_info);

	if (error)

		return error;

include/linux/hugetlb.h

+10 −0
Original line number Diff line number Diff line
@@ -412,6 +412,16 @@ static inline spinlock_t *huge_pte_lockptr(struct hstate *h, 
	return &mm->page_table_lock;

}



static inline bool hugepages_supported(void)

{

	/*

	 * Some platform decide whether they support huge pages at boot

	 * time. On these, such as powerpc, HPAGE_SHIFT is set to 0 when

	 * there is no such support

	 */

	return HPAGE_SHIFT != 0;

}



#else	/* CONFIG_HUGETLB_PAGE */

struct hstate {};

#define alloc_huge_page_node(h, nid) NULL

mm/hugetlb.c

+14 −5
Original line number Diff line number Diff line
@@ -1981,11 +1981,7 @@ static int __init hugetlb_init(void) 
{

	int i;



	/* Some platform decide whether they support huge pages at boot

	 * time. On these, such as powerpc, HPAGE_SHIFT is set to 0 when

	 * there is no such support

	 */

	if (HPAGE_SHIFT == 0)

	if (!hugepages_supported())

		return 0;



	if (!size_to_hstate(default_hstate_size)) {
@@ -2112,6 +2108,9 @@ static int hugetlb_sysctl_handler_common(bool obey_mempolicy, 
	unsigned long tmp;

	int ret;



	if (!hugepages_supported())

		return -ENOTSUPP;



	tmp = h->max_huge_pages;



	if (write && h->order >= MAX_ORDER)
@@ -2165,6 +2164,9 @@ int hugetlb_overcommit_handler(struct ctl_table *table, int write, 
	unsigned long tmp;

	int ret;



	if (!hugepages_supported())

		return -ENOTSUPP;



	tmp = h->nr_overcommit_huge_pages;



	if (write && h->order >= MAX_ORDER)
@@ -2190,6 +2192,8 @@ int hugetlb_overcommit_handler(struct ctl_table *table, int write, 
void hugetlb_report_meminfo(struct seq_file *m)

{

	struct hstate *h = &default_hstate;

	if (!hugepages_supported())

		return;

	seq_printf(m,

			"HugePages_Total:   %5lu\n"

			"HugePages_Free:    %5lu\n"
@@ -2206,6 +2210,8 @@ void hugetlb_report_meminfo(struct seq_file *m) 
int hugetlb_report_node_meminfo(int nid, char *buf)

{

	struct hstate *h = &default_hstate;

	if (!hugepages_supported())

		return 0;

	return sprintf(buf,

		"Node %d HugePages_Total: %5u\n"

		"Node %d HugePages_Free:  %5u\n"
@@ -2220,6 +2226,9 @@ void hugetlb_show_meminfo(void) 
	struct hstate *h;

	int nid;



	if (!hugepages_supported())

		return;



	for_each_node_state(nid, N_MEMORY)

		for_each_hstate(h)

			pr_info("Node %d hugepages_total=%u hugepages_free=%u hugepages_surp=%u hugepages_size=%lukB\n",