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From:   Roman Gushchin <guro@fb.com>
To:     Lucian Grijincu <lucian@fb.com>
CC:     "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Souptick Joarder <jrdr.linux@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Michal Hocko <mhocko@kernel.org>,
        "Andrew Morton" <akpm@linux-foundation.org>,
        Rik van Riel <riel@fb.com>
Subject: Re: [Potential Spoof] [PATCH v3] mm: memory: fix /proc/meminfo
 reporting for MLOCK_ONFAULT
Thread-Topic: [Potential Spoof] [PATCH v3] mm: memory: fix /proc/meminfo
 reporting for MLOCK_ONFAULT
Thread-Index: AQHVanfTSfRS6C+xc0+kVsEX6I4P3acqHD+A
Date:   Fri, 13 Sep 2019 21:17:08 +0000
Message-ID: <20190913211705.GA5392@tower.DHCP.thefacebook.com>
References: <20190913211119.416168-1-lucian@fb.com>
In-Reply-To: <20190913211119.416168-1-lucian@fb.com>
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On Fri, Sep 13, 2019 at 02:11:19PM -0700, Lucian Adrian Grijincu wrote:
> As pages are faulted in MLOCK_ONFAULT correctly updates
> /proc/self/smaps, but doesn't update /proc/meminfo's Mlocked field.
>=20
> - Before this /proc/meminfo fields didn't change as pages were faulted in=
:
>=20
> =3D Start =3D
> /proc/meminfo
> Unevictable:       10128 kB
> Mlocked:           10132 kB
> =3D Creating testfile =3D
>=20
> =3D after mlock2(MLOCK_ONFAULT) =3D
> /proc/meminfo
> Unevictable:       10128 kB
> Mlocked:           10132 kB
> /proc/self/smaps
> 7f8714000000-7f8754000000 rw-s 00000000 08:04 50857050   /root/testfile
> Locked:                0 kB
>=20
> =3D after reading half of the file =3D
> /proc/meminfo
> Unevictable:       10128 kB
> Mlocked:           10132 kB
> /proc/self/smaps
> 7f8714000000-7f8754000000 rw-s 00000000 08:04 50857050   /root/testfile
> Locked:           524288 kB
>=20
> =3D after reading the entire the file =3D
> /proc/meminfo
> Unevictable:       10128 kB
> Mlocked:           10132 kB
> /proc/self/smaps
> 7f8714000000-7f8754000000 rw-s 00000000 08:04 50857050   /root/testfile
> Locked:          1048576 kB
>=20
> =3D after munmap =3D
> /proc/meminfo
> Unevictable:       10128 kB
> Mlocked:           10132 kB
> /proc/self/smaps
>=20
> - After: /proc/meminfo fields are properly updated as pages are touched:
>=20
> =3D Start =3D
> /proc/meminfo
> Unevictable:          60 kB
> Mlocked:              60 kB
> =3D Creating testfile =3D
>=20
> =3D after mlock2(MLOCK_ONFAULT) =3D
> /proc/meminfo
> Unevictable:          60 kB
> Mlocked:              60 kB
> /proc/self/smaps
> 7f2b9c600000-7f2bdc600000 rw-s 00000000 08:04 63045798   /root/testfile
> Locked:                0 kB
>=20
> =3D after reading half of the file =3D
> /proc/meminfo
> Unevictable:      524220 kB
> Mlocked:          524220 kB
> /proc/self/smaps
> 7f2b9c600000-7f2bdc600000 rw-s 00000000 08:04 63045798   /root/testfile
> Locked:           524288 kB
>=20
> =3D after reading the entire the file =3D
> /proc/meminfo
> Unevictable:     1048496 kB
> Mlocked:         1048508 kB
> /proc/self/smaps
> 7f2b9c600000-7f2bdc600000 rw-s 00000000 08:04 63045798   /root/testfile
> Locked:          1048576 kB
>=20
> =3D after munmap =3D
> /proc/meminfo
> Unevictable:         176 kB
> Mlocked:              60 kB
> /proc/self/smaps
>=20
> Repro code.
> ---
>=20
> int mlock2wrap(const void* addr, size_t len, int flags) {
>   return syscall(SYS_mlock2, addr, len, flags);
> }
>=20
> void smaps() {
>   char smapscmd[1000];
>   snprintf(
>       smapscmd,
>       sizeof(smapscmd) - 1,
>       "grep testfile -A 20 /proc/%d/smaps | grep -E '(testfile|Locked)'",
>       getpid());
>   printf("/proc/self/smaps\n");
>   fflush(stdout);
>   system(smapscmd);
> }
>=20
> void meminfo() {
>   const char* meminfocmd =3D "grep -E '(Mlocked|Unevictable)' /proc/memin=
fo";
>   printf("/proc/meminfo\n");
>   fflush(stdout);
>   system(meminfocmd);
> }
>=20
>   {                                                 \
>     int rc =3D (call);                                \
>     if (rc !=3D 0) {                                  \
>       printf("error %d %s\n", rc, strerror(errno)); \
>       exit(1);                                      \
>     }                                               \
>   }
> int main(int argc, char* argv[]) {
>   printf("=3D Start =3D\n");
>   meminfo();
>=20
>   printf("=3D Creating testfile =3D\n");
>   size_t size =3D 1 << 30; // 1 GiB
>   int fd =3D open("testfile", O_CREAT | O_RDWR, 0666);
>   {
>     void* buf =3D malloc(size);
>     write(fd, buf, size);
>     free(buf);
>   }
>   int ret =3D 0;
>   void* addr =3D NULL;
>   addr =3D mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
>=20
>   if (argc > 1) {
>     PCHECK(mlock2wrap(addr, size, MLOCK_ONFAULT));
>     printf("=3D after mlock2(MLOCK_ONFAULT) =3D\n");
>     meminfo();
>     smaps();
>=20
>     for (size_t i =3D 0; i < size / 2; i +=3D 4096) {
>       ret +=3D ((char*)addr)[i];
>     }
>     printf("=3D after reading half of the file =3D\n");
>     meminfo();
>     smaps();
>=20
>     for (size_t i =3D 0; i < size; i +=3D 4096) {
>       ret +=3D ((char*)addr)[i];
>     }
>     printf("=3D after reading the entire the file =3D\n");
>     meminfo();
>     smaps();
>=20
>   } else {
>     PCHECK(mlock(addr, size));
>     printf("=3D after mlock =3D\n");
>     meminfo();
>     smaps();
>   }
>=20
>   PCHECK(munmap(addr, size));
>   printf("=3D after munmap =3D\n");
>   meminfo();
>   smaps();
>=20
>   return ret;
> }
>=20
> ---
>=20
> Signed-off-by: Lucian Adrian Grijincu <lucian@fb.com>
> Acked-by: Souptick Joarder <jrdr.linux@gmail.com>
> ---
>  mm/memory.c | 2 ++
>  1 file changed, 2 insertions(+)
>=20
> diff --git a/mm/memory.c b/mm/memory.c
> index e0c232fe81d9..55da24f33bc4 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3311,6 +3311,8 @@ vm_fault_t alloc_set_pte(struct vm_fault *vmf, stru=
ct mem_cgroup *memcg,
>  	} else {
>  		inc_mm_counter_fast(vma->vm_mm, mm_counter_file(page));
>  		page_add_file_rmap(page, false);
> +		if (vma->vm_flags & VM_LOCKED && !PageTransCompound(page))
> +			mlock_vma_page(page);

Acked-by: Roman Gushchin <guro@fb.com>

Thanks!