[PATCH 4.9 25/59] mm: madvise(MADV_DODUMP): allow hugetlbfs pages - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	stable@vger.kernel.org, Kenneth Penza <kpenza@gmail.com>,
	Daniel Black <daniel@linux.ibm.com>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Konstantin Khlebnikov <khlebnikov@openvz.org>,
	Andrew Morton <akpm@linux-foundation.org>
Subject: [PATCH 4.9 25/59] mm: madvise(MADV_DODUMP): allow hugetlbfs pages
Date: Mon,  8 Oct 2018 20:31:32 +0200	[thread overview]
Message-ID: <20181008175549.513885490@linuxfoundation.org> (raw)
In-Reply-To: <20181008175546.620836256@linuxfoundation.org>

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Daniel Black <daniel@linux.ibm.com>

commit d41aa5252394c065d1f04d1ceea885b70d00c9c6 upstream.

Reproducer, assuming 2M of hugetlbfs available:

Hugetlbfs mounted, size=2M and option user=testuser

  # mount | grep ^hugetlbfs
  hugetlbfs on /dev/hugepages type hugetlbfs (rw,pagesize=2M,user=dan)
  # sysctl vm.nr_hugepages=1
  vm.nr_hugepages = 1
  # grep Huge /proc/meminfo
  AnonHugePages:         0 kB
  ShmemHugePages:        0 kB
  HugePages_Total:       1
  HugePages_Free:        1
  HugePages_Rsvd:        0
  HugePages_Surp:        0
  Hugepagesize:       2048 kB
  Hugetlb:            2048 kB

Code:

  #include <sys/mman.h>
  #include <stddef.h>
  #define SIZE 2*1024*1024
  int main()
  {
    void *ptr;
    ptr = mmap(NULL, SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_HUGETLB | MAP_ANONYMOUS, -1, 0);
    madvise(ptr, SIZE, MADV_DONTDUMP);
    madvise(ptr, SIZE, MADV_DODUMP);
  }

Compile and strace:

  mmap(NULL, 2097152, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_HUGETLB, -1, 0) = 0x7ff7c9200000
  madvise(0x7ff7c9200000, 2097152, MADV_DONTDUMP) = 0
  madvise(0x7ff7c9200000, 2097152, MADV_DODUMP) = -1 EINVAL (Invalid argument)

hugetlbfs pages have VM_DONTEXPAND in the VmFlags driver pages based on
author testing with analysis from Florian Weimer[1].

The inclusion of VM_DONTEXPAND into the VM_SPECIAL defination was a
consequence of the large useage of VM_DONTEXPAND in device drivers.

A consequence of [2] is that VM_DONTEXPAND marked pages are unable to be
marked DODUMP.

A user could quite legitimately madvise(MADV_DONTDUMP) their hugetlbfs
memory for a while and later request that madvise(MADV_DODUMP) on the same
memory.  We correct this omission by allowing madvice(MADV_DODUMP) on
hugetlbfs pages.

[1] https://stackoverflow.com/questions/52548260/madvisedodump-on-the-same-ptr-size-as-a-successful-madvisedontdump-fails-wit
[2] commit 0103bd16fb90 ("mm: prepare VM_DONTDUMP for using in drivers")

Link: http://lkml.kernel.org/r/20180930054629.29150-1-daniel@linux.ibm.com
Link: https://lists.launchpad.net/maria-discuss/msg05245.html
Fixes: 0103bd16fb90 ("mm: prepare VM_DONTDUMP for using in drivers")
Reported-by: Kenneth Penza <kpenza@gmail.com>
Signed-off-by: Daniel Black <daniel@linux.ibm.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 mm/madvise.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -81,7 +81,7 @@ static long madvise_behavior(struct vm_a
 		new_flags |= VM_DONTDUMP;
 		break;
 	case MADV_DODUMP:
-		if (new_flags & VM_SPECIAL) {
+		if (!is_vm_hugetlb_page(vma) && new_flags & VM_SPECIAL) {
 			error = -EINVAL;
 			goto out;
 		}


