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memfd_create: simplify HUGETLB support a little bit

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This also fixes a minor issue that was missed in the initial review; the
layout of the MFD_HUGE_* flags is actually not 1:1 bit:flag -- it instead
borrowed the Linux convention of how this is laid out since it was
originally implemented on Linux, the top 6 bits represent the shift required
for the requested page size.

This allows us to remove the flag <-> pgsize mapping table and simplify the
logic just prior to validation of the requested page size.

While we're here, fix two small nits:

- HUGETLB memfd shouldn't exhibit the SHM_GROW_ON_WRITE behavior. We can
  only grow largepage shm by appropriately aligned (i.e. requested pagesize)
  sizes, so it can't work in the typical/sane fashion. Furthermore, Linux
  does the same, so let's be compatible.

- We don't allow MFD_HUGETLB without specifying a pagesize, so no need to
  check for that later.

Reviewed by:	kib (slightly earlier version)
This commit is contained in:
Kyle Evans 2020-09-11 02:02:15 +00:00
parent 0b39e3448a
commit 8b8cf4ece6
1 changed files with 14 additions and 45 deletions
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59
lib/libc/sys/shm_open.c
View File

@ -81,27 +81,6 @@ shm_create_largepage(const char *path, int flags, int psind, int alloc_policy,
return (fd);
}
#define K(x) ((size_t)(x) * 1024)
#define M(x) (K(x) * 1024)
#define G(x) (M(x) * 1024)
static const struct {
int mask;
size_t pgsize;
} mfd_huge_sizes[] = {
{ .mask = MFD_HUGE_64KB, .pgsize = K(64) },
{ .mask = MFD_HUGE_512KB, .pgsize = K(512) },
{ .mask = MFD_HUGE_1MB, .pgsize = M(1) },
{ .mask = MFD_HUGE_2MB, .pgsize = M(2) },
{ .mask = MFD_HUGE_8MB, .pgsize = M(8) },
{ .mask = MFD_HUGE_16MB, .pgsize = M(16) },
{ .mask = MFD_HUGE_32MB, .pgsize = M(32) },
{ .mask = MFD_HUGE_256MB, .pgsize = M(256) },
{ .mask = MFD_HUGE_512MB, .pgsize = M(512) },
{ .mask = MFD_HUGE_1GB, .pgsize = G(1) },
{ .mask = MFD_HUGE_2GB, .pgsize = G(2) },
{ .mask = MFD_HUGE_16GB, .pgsize = G(16) },
};
/*
* The path argument is passed to the kernel, but the kernel doesn't currently
* do anything with it. Linux exposes it in linprocfs for debugging purposes
@ -111,9 +90,9 @@ int
memfd_create(const char *name, unsigned int flags)
{
char memfd_name[NAME_MAX + 1];
size_t namelen, *pgs;
size_t namelen, *pgs, pgsize;
struct shm_largepage_conf slc;
int error, fd, i, npgs, oflags, pgidx, saved_errno, shmflags;
int error, fd, npgs, oflags, pgidx, saved_errno, shmflags;
if (name == NULL) {
errno = EBADF;
@ -130,8 +109,7 @@ memfd_create(const char *name, unsigned int flags)
return (-1);
}
/* Size specified but no HUGETLB. */
if (((flags & MFD_HUGE_MASK) != 0 && (flags & MFD_HUGETLB) == 0) ||
__bitcount(flags & MFD_HUGE_MASK) > 1) {
if ((flags & MFD_HUGE_MASK) != 0 && (flags & MFD_HUGETLB) == 0) {
errno = EINVAL;
return (-1);
}
@ -139,13 +117,15 @@ memfd_create(const char *name, unsigned int flags)
/* We've already validated that we're sufficiently sized. */
snprintf(memfd_name, NAME_MAX + 1, "%s%s", MEMFD_NAME_PREFIX, name);
oflags = O_RDWR;
shmflags = SHM_GROW_ON_WRITE;
shmflags = 0;
if ((flags & MFD_CLOEXEC) != 0)
oflags |= O_CLOEXEC;
if ((flags & MFD_ALLOW_SEALING) != 0)
shmflags |= SHM_ALLOW_SEALING;
if ((flags & MFD_HUGETLB) != 0)
shmflags |= SHM_LARGEPAGE;
else
shmflags |= SHM_GROW_ON_WRITE;
fd = __sys_shm_open2(SHM_ANON, oflags, 0, shmflags, memfd_name);
if (fd == -1 || (flags & MFD_HUGETLB) == 0)
return (fd);
@ -160,25 +140,14 @@ memfd_create(const char *name, unsigned int flags)
error = getpagesizes(pgs, npgs);
if (error == -1)
goto clean;
if ((flags & MFD_HUGE_MASK) == 0) {
if (npgs == 1) {
errno = EOPNOTSUPP;
goto clean;
}
pgidx = 1;
} else {
for (i = 0; i < nitems(mfd_huge_sizes); i++) {
if (mfd_huge_sizes[i].mask == (flags & MFD_HUGE_MASK))
break;
}
for (pgidx = 0; pgidx < npgs; pgidx++) {
if (mfd_huge_sizes[i].pgsize == pgs[pgidx])
break;
}
if (pgidx == npgs) {
errno = EOPNOTSUPP;
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;
goto clean;
}
free(pgs);
pgs = NULL;