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libc: fix memfd_create's HUGETLB handling

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The 'simplification' commit referenced below actually broke one aspect
of MFD_HUGETLB: the caller isn't supposed to be required to specify a
size.  MFD_HUGETLB by itself without a shift mask just requests a large
page, so we revert that part of memfd_create() back.

While we're here, fix up the related parts of the manpages a little bit,
since MFD_HUGETLB is actually supported.  The manpage claims that we
would return ENOSYS if forced mappings weren't supported, but this was
actually not true.  However, that seems like a very important
distinction to make between ENOSYS and EOPNOTSUPP, so fix the
implementation to match the docs.

Reviewed by:	kib, markj

(cherry picked from commit 9a8d333368baef356f0a611b47ec592568dd14f9)
This commit is contained in:
Kyle Evans 2026-04-08 21:37:00 -05:00
parent 65e1c27b4b
commit ac6173b54f
5 changed files with 136 additions and 36 deletions
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23
lib/libc/gen/memfd_create.c
View file

@ -95,16 +95,25 @@ memfd_create(const char *name, unsigned int flags)
npgs = getpagesizes(pgs, nitems(pgs));
if (npgs == -1)
goto clean;
pgsize = (size_t)1 << ((flags & MFD_HUGE_MASK) >> MFD_HUGE_SHIFT);
for (pgidx = 0; pgidx < npgs; pgidx++) {
if (pgsize == pgs[pgidx])
break;
}
if (pgidx == npgs) {
errno = EOPNOTSUPP;
else if (npgs == 1) {
errno = ENOSYS;
goto clean;
}
if ((flags & MFD_HUGE_MASK) == 0) {
pgidx = 1;
} else {
pgsize = 1UL << ((flags & MFD_HUGE_MASK) >> MFD_HUGE_SHIFT);
for (pgidx = 1; pgidx < npgs; pgidx++) {
if (pgsize == pgs[pgidx])
break;
}
if (pgidx == npgs) {
errno = EOPNOTSUPP;
goto clean;
}
}
memset(&slc, 0, sizeof(slc));
slc.psind = pgidx;
slc.alloc_policy = SHM_LARGEPAGE_ALLOC_DEFAULT;

31
lib/libsys/shm_open.2
View file

@ -26,7 +26,7 @@
.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd August 4, 2025
.Dd March 26, 2025
.Dt SHM_OPEN 2
.Os
.Sh NAME
@ -343,7 +343,25 @@ Allow adding seals to the resulting file descriptor using the
.Xr fcntl 2
command.
.It Dv MFD_HUGETLB
This flag is currently unsupported.
Create a memfd backed by a
.Dq largepage
object.
One of the
.Dv MFD_HUGE_*
flags defined in
.In sys/mman.h
may be included to specify a fixed size.
If a specific size is not requested, the smallest supported large page size is
selected.
.Pp
The behavior documented above for the
.Fn shm_create_largepage
.Fa psind
argument also applies to largepage objects created by
.Fn memfd_create ,
and the
.Dv SHM_LARGEPAGE_ALLOC_DEFAULT
policy will always be used.
.El
.Sh RETURN VALUES
If successful,
@ -458,17 +476,22 @@ argument was too long.
.Pp
An invalid or unsupported flag was included in
.Fa flags .
.It Bq Er EINVAL
A hugetlb mapping was requested, but
.Dv MFD_HUGETLB
was not specified in
.Fa flags .
.It Bq Er EMFILE
The process has already reached its limit for open file descriptors.
.It Bq Er ENFILE
The system file table is full.
.It Bq Er ENOSYS
In
.Fa memfd_create ,
.Dv MFD_HUGETLB
was specified in
.Fa flags ,
and this system does not support forced hugetlb mappings.
.It Bq Er EOPNOTSUPP
This system does not support the requested hugetlb page size.
.El
.Pp
.Fn shm_open

35
tests/sys/posixshm/memfd_test.c
View file

@ -34,6 +34,8 @@
#include <errno.h>
#include <unistd.h>
#include "posixshm.h"
ATF_TC_WITHOUT_HEAD(basic);
ATF_TC_BODY(basic, tc)
{
@ -277,6 +279,38 @@ ATF_TC_BODY(immutable_seals, tc)
close(fd);
}
ATF_TC_WITHOUT_HEAD(hugetlb);
ATF_TC_BODY(hugetlb, tc)
{
size_t ps[MAXPAGESIZES], pgsize;
int fd, pscnt;
pscnt = pagesizes(ps, false);
#define MFD_HUGE_SUPPORTED(sz) (sz <= (1 << 24))
#define MFD_HUGE_FLAGS(sz) (((ffsl(sz) - 1U) << MFD_HUGE_SHIFT) & MFD_HUGE_MASK)
for (int psidx = 1; psidx < pscnt; psidx++) {
pgsize = ps[psidx];
if (!MFD_HUGE_SUPPORTED(pgsize))
continue;
ATF_REQUIRE_MSG((fd = memfd_create("...",
MFD_HUGETLB | MFD_HUGE_FLAGS(pgsize))) != -1,
"Creating a %zu-size hugetlb memfd", pgsize);
}
fd = memfd_create("...", MFD_HUGETLB);
if (pscnt == 1) {
ATF_REQUIRE_MSG(fd == -1,
"Creating an unspecified hugetlb memfd without large page support");
ATF_REQUIRE(errno == ENOSYS);
} else {
ATF_REQUIRE_MSG(fd != -1,
"Creating an unspecified hugetlb memfd with large page support");
close(fd);
}
}
ATF_TP_ADD_TCS(tp)
{
@ -289,5 +323,6 @@ ATF_TP_ADD_TCS(tp)
ATF_TP_ADD_TC(tp, get_seals);
ATF_TP_ADD_TC(tp, dup_seals);
ATF_TP_ADD_TC(tp, immutable_seals);
ATF_TP_ADD_TC(tp, hugetlb);
return (atf_no_error());
}

45
tests/sys/posixshm/posixshm.h Normal file
View file

@ -0,0 +1,45 @@
/*-
*
* Copyright (c) 2020 Klara, Inc.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/
#include <sys/param.h>
#include <sys/mman.h>
#include <stdbool.h>
static int
pagesizes(size_t ps[MAXPAGESIZES], bool required)
{
int pscnt;
pscnt = getpagesizes(ps, MAXPAGESIZES);
ATF_REQUIRE_MSG(pscnt != -1, "getpagesizes failed; errno=%d", errno);
ATF_REQUIRE_MSG(ps[0] != 0, "psind 0 is %zu", ps[0]);
ATF_REQUIRE_MSG(pscnt <= MAXPAGESIZES, "invalid pscnt %d", pscnt);
if (pscnt == 1 && required)
atf_tc_skip("no large page support");
return (pscnt);
}

38
tests/sys/posixshm/posixshm_test.c
View file

@ -49,6 +49,8 @@
#include <atf-c.h>
#include "posixshm.h"
#define TEST_PATH_LEN 256
static char test_path[TEST_PATH_LEN];
static char test_path2[TEST_PATH_LEN];
@ -1239,20 +1241,6 @@ shm_open_large(int psind, int policy, size_t sz)
return (fd);
}
static int
pagesizes(size_t ps[MAXPAGESIZES])
{
int pscnt;
pscnt = getpagesizes(ps, MAXPAGESIZES);
ATF_REQUIRE_MSG(pscnt != -1, "getpagesizes failed; errno=%d", errno);
ATF_REQUIRE_MSG(ps[0] != 0, "psind 0 is %zu", ps[0]);
ATF_REQUIRE_MSG(pscnt <= MAXPAGESIZES, "invalid pscnt %d", pscnt);
if (pscnt == 1)
atf_tc_skip("no large page support");
return (pscnt);
}
ATF_TC_WITHOUT_HEAD(largepage_basic);
ATF_TC_BODY(largepage_basic, tc)
{
@ -1261,7 +1249,7 @@ ATF_TC_BODY(largepage_basic, tc)
size_t ps[MAXPAGESIZES];
int error, fd, pscnt;
pscnt = pagesizes(ps);
pscnt = pagesizes(ps, true);
zeroes = calloc(1, ps[0]);
ATF_REQUIRE(zeroes != NULL);
for (int i = 1; i < pscnt; i++) {
@ -1317,7 +1305,7 @@ ATF_TC_BODY(largepage_config, tc)
size_t ps[MAXPAGESIZES + 1]; /* silence warnings if MAXPAGESIZES == 1 */
int error, fd;
(void)pagesizes(ps);
(void)pagesizes(ps, true);
fd = shm_open(SHM_ANON, O_CREAT | O_RDWR, 0);
ATF_REQUIRE_MSG(fd >= 0, "shm_open failed; error=%d", errno);
@ -1379,7 +1367,7 @@ ATF_TC_BODY(largepage_mmap, tc)
size_t ps[MAXPAGESIZES];
int fd, pscnt;
pscnt = pagesizes(ps);
pscnt = pagesizes(ps, true);
for (int i = 1; i < pscnt; i++) {
fd = shm_open_large(i, SHM_LARGEPAGE_ALLOC_DEFAULT, ps[i]);
@ -1475,7 +1463,7 @@ ATF_TC_BODY(largepage_munmap, tc)
size_t ps[MAXPAGESIZES], ps1;
int fd, pscnt;
pscnt = pagesizes(ps);
pscnt = pagesizes(ps, true);
for (int i = 1; i < pscnt; i++) {
fd = shm_open_large(i, SHM_LARGEPAGE_ALLOC_DEFAULT, ps[i]);
ps1 = ps[i - 1];
@ -1526,7 +1514,7 @@ ATF_TC_BODY(largepage_madvise, tc)
size_t ps[MAXPAGESIZES];
int fd, pscnt;
pscnt = pagesizes(ps);
pscnt = pagesizes(ps, true);
for (int i = 1; i < pscnt; i++) {
fd = shm_open_large(i, SHM_LARGEPAGE_ALLOC_DEFAULT, ps[i]);
addr = mmap(NULL, ps[i], PROT_READ | PROT_WRITE, MAP_SHARED, fd,
@ -1595,7 +1583,7 @@ ATF_TC_BODY(largepage_mlock, tc)
"sysctlbyname(vm.stats.vm.v_user_wire_count) failed; error=%d",
errno);
pscnt = pagesizes(ps);
pscnt = pagesizes(ps, true);
for (int i = 1; i < pscnt; i++) {
if (ps[i] / ps[0] > max_wired - wired) {
/* Cannot wire past the limit. */
@ -1638,7 +1626,7 @@ ATF_TC_BODY(largepage_msync, tc)
size_t ps[MAXPAGESIZES];
int fd, pscnt;
pscnt = pagesizes(ps);
pscnt = pagesizes(ps, true);
for (int i = 1; i < pscnt; i++) {
fd = shm_open_large(i, SHM_LARGEPAGE_ALLOC_DEFAULT, ps[i]);
addr = mmap(NULL, ps[i], PROT_READ | PROT_WRITE, MAP_SHARED, fd,
@ -1697,7 +1685,7 @@ ATF_TC_BODY(largepage_mprotect, tc)
size_t ps[MAXPAGESIZES];
int fd, pscnt;
pscnt = pagesizes(ps);
pscnt = pagesizes(ps, true);
for (int i = 1; i < pscnt; i++) {
/*
* Reserve a contiguous region in the address space to avoid
@ -1767,7 +1755,7 @@ ATF_TC_BODY(largepage_minherit, tc)
pid_t child;
int fd, pscnt, status;
pscnt = pagesizes(ps);
pscnt = pagesizes(ps, true);
for (int i = 1; i < pscnt; i++) {
fd = shm_open_large(i, SHM_LARGEPAGE_ALLOC_DEFAULT, ps[i]);
addr = mmap(NULL, ps[i], PROT_READ | PROT_WRITE, MAP_SHARED, fd,
@ -1855,7 +1843,7 @@ ATF_TC_BODY(largepage_pipe, tc)
int fd, pfd[2], pscnt, status;
pid_t child;
pscnt = pagesizes(ps);
pscnt = pagesizes(ps, true);
for (int i = 1; i < pscnt; i++) {
fd = shm_open_large(i, SHM_LARGEPAGE_ALLOC_DEFAULT, ps[i]);
@ -1908,7 +1896,7 @@ ATF_TC_BODY(largepage_reopen, tc)
size_t ps[MAXPAGESIZES];
int fd, psind;
(void)pagesizes(ps);
(void)pagesizes(ps, true);
psind = 1;
gen_test_path();