linuxdebug/mm/mlock.c

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2024-07-16 15:50:57 +02:00
// SPDX-License-Identifier: GPL-2.0
/*
* linux/mm/mlock.c
*
* (C) Copyright 1995 Linus Torvalds
* (C) Copyright 2002 Christoph Hellwig
*/
#include <linux/capability.h>
#include <linux/mman.h>
#include <linux/mm.h>
#include <linux/sched/user.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/pagemap.h>
#include <linux/pagevec.h>
#include <linux/pagewalk.h>
#include <linux/mempolicy.h>
#include <linux/syscalls.h>
#include <linux/sched.h>
#include <linux/export.h>
#include <linux/rmap.h>
#include <linux/mmzone.h>
#include <linux/hugetlb.h>
#include <linux/memcontrol.h>
#include <linux/mm_inline.h>
#include <linux/secretmem.h>
#include "internal.h"
struct mlock_pvec {
local_lock_t lock;
struct pagevec vec;
};
static DEFINE_PER_CPU(struct mlock_pvec, mlock_pvec) = {
.lock = INIT_LOCAL_LOCK(lock),
};
bool can_do_mlock(void)
{
if (rlimit(RLIMIT_MEMLOCK) != 0)
return true;
if (capable(CAP_IPC_LOCK))
return true;
return false;
}
EXPORT_SYMBOL(can_do_mlock);
/*
* Mlocked pages are marked with PageMlocked() flag for efficient testing
* in vmscan and, possibly, the fault path; and to support semi-accurate
* statistics.
*
* An mlocked page [PageMlocked(page)] is unevictable. As such, it will
* be placed on the LRU "unevictable" list, rather than the [in]active lists.
* The unevictable list is an LRU sibling list to the [in]active lists.
* PageUnevictable is set to indicate the unevictable state.
*/
static struct lruvec *__mlock_page(struct page *page, struct lruvec *lruvec)
{
/* There is nothing more we can do while it's off LRU */
if (!TestClearPageLRU(page))
return lruvec;
lruvec = folio_lruvec_relock_irq(page_folio(page), lruvec);
if (unlikely(page_evictable(page))) {
/*
* This is a little surprising, but quite possible:
* PageMlocked must have got cleared already by another CPU.
* Could this page be on the Unevictable LRU? I'm not sure,
* but move it now if so.
*/
if (PageUnevictable(page)) {
del_page_from_lru_list(page, lruvec);
ClearPageUnevictable(page);
add_page_to_lru_list(page, lruvec);
__count_vm_events(UNEVICTABLE_PGRESCUED,
thp_nr_pages(page));
}
goto out;
}
if (PageUnevictable(page)) {
if (PageMlocked(page))
page->mlock_count++;
goto out;
}
del_page_from_lru_list(page, lruvec);
ClearPageActive(page);
SetPageUnevictable(page);
page->mlock_count = !!PageMlocked(page);
add_page_to_lru_list(page, lruvec);
__count_vm_events(UNEVICTABLE_PGCULLED, thp_nr_pages(page));
out:
SetPageLRU(page);
return lruvec;
}
static struct lruvec *__mlock_new_page(struct page *page, struct lruvec *lruvec)
{
VM_BUG_ON_PAGE(PageLRU(page), page);
lruvec = folio_lruvec_relock_irq(page_folio(page), lruvec);
/* As above, this is a little surprising, but possible */
if (unlikely(page_evictable(page)))
goto out;
SetPageUnevictable(page);
page->mlock_count = !!PageMlocked(page);
__count_vm_events(UNEVICTABLE_PGCULLED, thp_nr_pages(page));
out:
add_page_to_lru_list(page, lruvec);
SetPageLRU(page);
return lruvec;
}
static struct lruvec *__munlock_page(struct page *page, struct lruvec *lruvec)
{
int nr_pages = thp_nr_pages(page);
bool isolated = false;
if (!TestClearPageLRU(page))
goto munlock;
isolated = true;
lruvec = folio_lruvec_relock_irq(page_folio(page), lruvec);
if (PageUnevictable(page)) {
/* Then mlock_count is maintained, but might undercount */
if (page->mlock_count)
page->mlock_count--;
if (page->mlock_count)
goto out;
}
/* else assume that was the last mlock: reclaim will fix it if not */
munlock:
if (TestClearPageMlocked(page)) {
__mod_zone_page_state(page_zone(page), NR_MLOCK, -nr_pages);
if (isolated || !PageUnevictable(page))
__count_vm_events(UNEVICTABLE_PGMUNLOCKED, nr_pages);
else
__count_vm_events(UNEVICTABLE_PGSTRANDED, nr_pages);
}
/* page_evictable() has to be checked *after* clearing Mlocked */
if (isolated && PageUnevictable(page) && page_evictable(page)) {
del_page_from_lru_list(page, lruvec);
ClearPageUnevictable(page);
add_page_to_lru_list(page, lruvec);
__count_vm_events(UNEVICTABLE_PGRESCUED, nr_pages);
}
out:
if (isolated)
SetPageLRU(page);
return lruvec;
}
/*
* Flags held in the low bits of a struct page pointer on the mlock_pvec.
*/
#define LRU_PAGE 0x1
#define NEW_PAGE 0x2
static inline struct page *mlock_lru(struct page *page)
{
return (struct page *)((unsigned long)page + LRU_PAGE);
}
static inline struct page *mlock_new(struct page *page)
{
return (struct page *)((unsigned long)page + NEW_PAGE);
}
/*
* mlock_pagevec() is derived from pagevec_lru_move_fn():
* perhaps that can make use of such page pointer flags in future,
* but for now just keep it for mlock. We could use three separate
* pagevecs instead, but one feels better (munlocking a full pagevec
* does not need to drain mlocking pagevecs first).
*/
static void mlock_pagevec(struct pagevec *pvec)
{
struct lruvec *lruvec = NULL;
unsigned long mlock;
struct page *page;
int i;
for (i = 0; i < pagevec_count(pvec); i++) {
page = pvec->pages[i];
mlock = (unsigned long)page & (LRU_PAGE | NEW_PAGE);
page = (struct page *)((unsigned long)page - mlock);
pvec->pages[i] = page;
if (mlock & LRU_PAGE)
lruvec = __mlock_page(page, lruvec);
else if (mlock & NEW_PAGE)
lruvec = __mlock_new_page(page, lruvec);
else
lruvec = __munlock_page(page, lruvec);
}
if (lruvec)
unlock_page_lruvec_irq(lruvec);
release_pages(pvec->pages, pvec->nr);
pagevec_reinit(pvec);
}
void mlock_page_drain_local(void)
{
struct pagevec *pvec;
local_lock(&mlock_pvec.lock);
pvec = this_cpu_ptr(&mlock_pvec.vec);
if (pagevec_count(pvec))
mlock_pagevec(pvec);
local_unlock(&mlock_pvec.lock);
}
void mlock_page_drain_remote(int cpu)
{
struct pagevec *pvec;
WARN_ON_ONCE(cpu_online(cpu));
pvec = &per_cpu(mlock_pvec.vec, cpu);
if (pagevec_count(pvec))
mlock_pagevec(pvec);
}
bool need_mlock_page_drain(int cpu)
{
return pagevec_count(&per_cpu(mlock_pvec.vec, cpu));
}
/**
* mlock_folio - mlock a folio already on (or temporarily off) LRU
* @folio: folio to be mlocked.
*/
void mlock_folio(struct folio *folio)
{
struct pagevec *pvec;
local_lock(&mlock_pvec.lock);
pvec = this_cpu_ptr(&mlock_pvec.vec);
if (!folio_test_set_mlocked(folio)) {
int nr_pages = folio_nr_pages(folio);
zone_stat_mod_folio(folio, NR_MLOCK, nr_pages);
__count_vm_events(UNEVICTABLE_PGMLOCKED, nr_pages);
}
folio_get(folio);
if (!pagevec_add(pvec, mlock_lru(&folio->page)) ||
folio_test_large(folio) || lru_cache_disabled())
mlock_pagevec(pvec);
local_unlock(&mlock_pvec.lock);
}
/**
* mlock_new_page - mlock a newly allocated page not yet on LRU
* @page: page to be mlocked, either a normal page or a THP head.
*/
void mlock_new_page(struct page *page)
{
struct pagevec *pvec;
int nr_pages = thp_nr_pages(page);
local_lock(&mlock_pvec.lock);
pvec = this_cpu_ptr(&mlock_pvec.vec);
SetPageMlocked(page);
mod_zone_page_state(page_zone(page), NR_MLOCK, nr_pages);
__count_vm_events(UNEVICTABLE_PGMLOCKED, nr_pages);
get_page(page);
if (!pagevec_add(pvec, mlock_new(page)) ||
PageHead(page) || lru_cache_disabled())
mlock_pagevec(pvec);
local_unlock(&mlock_pvec.lock);
}
/**
* munlock_page - munlock a page
* @page: page to be munlocked, either a normal page or a THP head.
*/
void munlock_page(struct page *page)
{
struct pagevec *pvec;
local_lock(&mlock_pvec.lock);
pvec = this_cpu_ptr(&mlock_pvec.vec);
/*
* TestClearPageMlocked(page) must be left to __munlock_page(),
* which will check whether the page is multiply mlocked.
*/
get_page(page);
if (!pagevec_add(pvec, page) ||
PageHead(page) || lru_cache_disabled())
mlock_pagevec(pvec);
local_unlock(&mlock_pvec.lock);
}
static int mlock_pte_range(pmd_t *pmd, unsigned long addr,
unsigned long end, struct mm_walk *walk)
{
struct vm_area_struct *vma = walk->vma;
spinlock_t *ptl;
pte_t *start_pte, *pte;
struct page *page;
ptl = pmd_trans_huge_lock(pmd, vma);
if (ptl) {
if (!pmd_present(*pmd))
goto out;
if (is_huge_zero_pmd(*pmd))
goto out;
page = pmd_page(*pmd);
if (vma->vm_flags & VM_LOCKED)
mlock_folio(page_folio(page));
else
munlock_page(page);
goto out;
}
start_pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
for (pte = start_pte; addr != end; pte++, addr += PAGE_SIZE) {
if (!pte_present(*pte))
continue;
page = vm_normal_page(vma, addr, *pte);
if (!page || is_zone_device_page(page))
continue;
if (PageTransCompound(page))
continue;
if (vma->vm_flags & VM_LOCKED)
mlock_folio(page_folio(page));
else
munlock_page(page);
}
pte_unmap(start_pte);
out:
spin_unlock(ptl);
cond_resched();
return 0;
}
/*
* mlock_vma_pages_range() - mlock any pages already in the range,
* or munlock all pages in the range.
* @vma - vma containing range to be mlock()ed or munlock()ed
* @start - start address in @vma of the range
* @end - end of range in @vma
* @newflags - the new set of flags for @vma.
*
* Called for mlock(), mlock2() and mlockall(), to set @vma VM_LOCKED;
* called for munlock() and munlockall(), to clear VM_LOCKED from @vma.
*/
static void mlock_vma_pages_range(struct vm_area_struct *vma,
unsigned long start, unsigned long end, vm_flags_t newflags)
{
static const struct mm_walk_ops mlock_walk_ops = {
.pmd_entry = mlock_pte_range,
};
/*
* There is a slight chance that concurrent page migration,
* or page reclaim finding a page of this now-VM_LOCKED vma,
* will call mlock_vma_page() and raise page's mlock_count:
* double counting, leaving the page unevictable indefinitely.
* Communicate this danger to mlock_vma_page() with VM_IO,
* which is a VM_SPECIAL flag not allowed on VM_LOCKED vmas.
* mmap_lock is held in write mode here, so this weird
* combination should not be visible to other mmap_lock users;
* but WRITE_ONCE so rmap walkers must see VM_IO if VM_LOCKED.
*/
if (newflags & VM_LOCKED)
newflags |= VM_IO;
WRITE_ONCE(vma->vm_flags, newflags);
lru_add_drain();
walk_page_range(vma->vm_mm, start, end, &mlock_walk_ops, NULL);
lru_add_drain();
if (newflags & VM_IO) {
newflags &= ~VM_IO;
WRITE_ONCE(vma->vm_flags, newflags);
}
}
/*
* mlock_fixup - handle mlock[all]/munlock[all] requests.
*
* Filters out "special" vmas -- VM_LOCKED never gets set for these, and
* munlock is a no-op. However, for some special vmas, we go ahead and
* populate the ptes.
*
* For vmas that pass the filters, merge/split as appropriate.
*/
static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
unsigned long start, unsigned long end, vm_flags_t newflags)
{
struct mm_struct *mm = vma->vm_mm;
pgoff_t pgoff;
int nr_pages;
int ret = 0;
vm_flags_t oldflags = vma->vm_flags;
if (newflags == oldflags || (oldflags & VM_SPECIAL) ||
is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm) ||
vma_is_dax(vma) || vma_is_secretmem(vma))
/* don't set VM_LOCKED or VM_LOCKONFAULT and don't count */
goto out;
pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
*prev = vma_merge(mm, *prev, start, end, newflags, vma->anon_vma,
vma->vm_file, pgoff, vma_policy(vma),
vma->vm_userfaultfd_ctx, anon_vma_name(vma));
if (*prev) {
vma = *prev;
goto success;
}
if (start != vma->vm_start) {
ret = split_vma(mm, vma, start, 1);
if (ret)
goto out;
}
if (end != vma->vm_end) {
ret = split_vma(mm, vma, end, 0);
if (ret)
goto out;
}
success:
/*
* Keep track of amount of locked VM.
*/
nr_pages = (end - start) >> PAGE_SHIFT;
if (!(newflags & VM_LOCKED))
nr_pages = -nr_pages;
else if (oldflags & VM_LOCKED)
nr_pages = 0;
mm->locked_vm += nr_pages;
/*
* vm_flags is protected by the mmap_lock held in write mode.
* It's okay if try_to_unmap_one unmaps a page just after we
* set VM_LOCKED, populate_vma_page_range will bring it back.
*/
if ((newflags & VM_LOCKED) && (oldflags & VM_LOCKED)) {
/* No work to do, and mlocking twice would be wrong */
vma->vm_flags = newflags;
} else {
mlock_vma_pages_range(vma, start, end, newflags);
}
out:
*prev = vma;
return ret;
}
static int apply_vma_lock_flags(unsigned long start, size_t len,
vm_flags_t flags)
{
unsigned long nstart, end, tmp;
struct vm_area_struct *vma, *prev;
int error;
MA_STATE(mas, &current->mm->mm_mt, start, start);
VM_BUG_ON(offset_in_page(start));
VM_BUG_ON(len != PAGE_ALIGN(len));
end = start + len;
if (end < start)
return -EINVAL;
if (end == start)
return 0;
vma = mas_walk(&mas);
if (!vma)
return -ENOMEM;
if (start > vma->vm_start)
prev = vma;
else
prev = mas_prev(&mas, 0);
for (nstart = start ; ; ) {
vm_flags_t newflags = vma->vm_flags & VM_LOCKED_CLEAR_MASK;
newflags |= flags;
/* Here we know that vma->vm_start <= nstart < vma->vm_end. */
tmp = vma->vm_end;
if (tmp > end)
tmp = end;
error = mlock_fixup(vma, &prev, nstart, tmp, newflags);
if (error)
break;
nstart = tmp;
if (nstart < prev->vm_end)
nstart = prev->vm_end;
if (nstart >= end)
break;
vma = find_vma(prev->vm_mm, prev->vm_end);
if (!vma || vma->vm_start != nstart) {
error = -ENOMEM;
break;
}
}
return error;
}
/*
* Go through vma areas and sum size of mlocked
* vma pages, as return value.
* Note deferred memory locking case(mlock2(,,MLOCK_ONFAULT)
* is also counted.
* Return value: previously mlocked page counts
*/
static unsigned long count_mm_mlocked_page_nr(struct mm_struct *mm,
unsigned long start, size_t len)
{
struct vm_area_struct *vma;
unsigned long count = 0;
unsigned long end;
VMA_ITERATOR(vmi, mm, start);
/* Don't overflow past ULONG_MAX */
if (unlikely(ULONG_MAX - len < start))
end = ULONG_MAX;
else
end = start + len;
for_each_vma_range(vmi, vma, end) {
if (vma->vm_flags & VM_LOCKED) {
if (start > vma->vm_start)
count -= (start - vma->vm_start);
if (end < vma->vm_end) {
count += end - vma->vm_start;
break;
}
count += vma->vm_end - vma->vm_start;
}
}
return count >> PAGE_SHIFT;
}
/*
* convert get_user_pages() return value to posix mlock() error
*/
static int __mlock_posix_error_return(long retval)
{
if (retval == -EFAULT)
retval = -ENOMEM;
else if (retval == -ENOMEM)
retval = -EAGAIN;
return retval;
}
static __must_check int do_mlock(unsigned long start, size_t len, vm_flags_t flags)
{
unsigned long locked;
unsigned long lock_limit;
int error = -ENOMEM;
start = untagged_addr(start);
if (!can_do_mlock())
return -EPERM;
len = PAGE_ALIGN(len + (offset_in_page(start)));
start &= PAGE_MASK;
lock_limit = rlimit(RLIMIT_MEMLOCK);
lock_limit >>= PAGE_SHIFT;
locked = len >> PAGE_SHIFT;
if (mmap_write_lock_killable(current->mm))
return -EINTR;
locked += current->mm->locked_vm;
if ((locked > lock_limit) && (!capable(CAP_IPC_LOCK))) {
/*
* It is possible that the regions requested intersect with
* previously mlocked areas, that part area in "mm->locked_vm"
* should not be counted to new mlock increment count. So check
* and adjust locked count if necessary.
*/
locked -= count_mm_mlocked_page_nr(current->mm,
start, len);
}
/* check against resource limits */
if ((locked <= lock_limit) || capable(CAP_IPC_LOCK))
error = apply_vma_lock_flags(start, len, flags);
mmap_write_unlock(current->mm);
if (error)
return error;
error = __mm_populate(start, len, 0);
if (error)
return __mlock_posix_error_return(error);
return 0;
}
SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
{
return do_mlock(start, len, VM_LOCKED);
}
SYSCALL_DEFINE3(mlock2, unsigned long, start, size_t, len, int, flags)
{
vm_flags_t vm_flags = VM_LOCKED;
if (flags & ~MLOCK_ONFAULT)
return -EINVAL;
if (flags & MLOCK_ONFAULT)
vm_flags |= VM_LOCKONFAULT;
return do_mlock(start, len, vm_flags);
}
SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
{
int ret;
start = untagged_addr(start);
len = PAGE_ALIGN(len + (offset_in_page(start)));
start &= PAGE_MASK;
if (mmap_write_lock_killable(current->mm))
return -EINTR;
ret = apply_vma_lock_flags(start, len, 0);
mmap_write_unlock(current->mm);
return ret;
}
/*
* Take the MCL_* flags passed into mlockall (or 0 if called from munlockall)
* and translate into the appropriate modifications to mm->def_flags and/or the
* flags for all current VMAs.
*
* There are a couple of subtleties with this. If mlockall() is called multiple
* times with different flags, the values do not necessarily stack. If mlockall
* is called once including the MCL_FUTURE flag and then a second time without
* it, VM_LOCKED and VM_LOCKONFAULT will be cleared from mm->def_flags.
*/
static int apply_mlockall_flags(int flags)
{
MA_STATE(mas, &current->mm->mm_mt, 0, 0);
struct vm_area_struct *vma, *prev = NULL;
vm_flags_t to_add = 0;
current->mm->def_flags &= VM_LOCKED_CLEAR_MASK;
if (flags & MCL_FUTURE) {
current->mm->def_flags |= VM_LOCKED;
if (flags & MCL_ONFAULT)
current->mm->def_flags |= VM_LOCKONFAULT;
if (!(flags & MCL_CURRENT))
goto out;
}
if (flags & MCL_CURRENT) {
to_add |= VM_LOCKED;
if (flags & MCL_ONFAULT)
to_add |= VM_LOCKONFAULT;
}
mas_for_each(&mas, vma, ULONG_MAX) {
vm_flags_t newflags;
newflags = vma->vm_flags & VM_LOCKED_CLEAR_MASK;
newflags |= to_add;
/* Ignore errors */
mlock_fixup(vma, &prev, vma->vm_start, vma->vm_end, newflags);
mas_pause(&mas);
cond_resched();
}
out:
return 0;
}
SYSCALL_DEFINE1(mlockall, int, flags)
{
unsigned long lock_limit;
int ret;
if (!flags || (flags & ~(MCL_CURRENT | MCL_FUTURE | MCL_ONFAULT)) ||
flags == MCL_ONFAULT)
return -EINVAL;
if (!can_do_mlock())
return -EPERM;
lock_limit = rlimit(RLIMIT_MEMLOCK);
lock_limit >>= PAGE_SHIFT;
if (mmap_write_lock_killable(current->mm))
return -EINTR;
ret = -ENOMEM;
if (!(flags & MCL_CURRENT) || (current->mm->total_vm <= lock_limit) ||
capable(CAP_IPC_LOCK))
ret = apply_mlockall_flags(flags);
mmap_write_unlock(current->mm);
if (!ret && (flags & MCL_CURRENT))
mm_populate(0, TASK_SIZE);
return ret;
}
SYSCALL_DEFINE0(munlockall)
{
int ret;
if (mmap_write_lock_killable(current->mm))
return -EINTR;
ret = apply_mlockall_flags(0);
mmap_write_unlock(current->mm);
return ret;
}
/*
* Objects with different lifetime than processes (SHM_LOCK and SHM_HUGETLB
* shm segments) get accounted against the user_struct instead.
*/
static DEFINE_SPINLOCK(shmlock_user_lock);
int user_shm_lock(size_t size, struct ucounts *ucounts)
{
unsigned long lock_limit, locked;
long memlock;
int allowed = 0;
locked = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
lock_limit = rlimit(RLIMIT_MEMLOCK);
if (lock_limit != RLIM_INFINITY)
lock_limit >>= PAGE_SHIFT;
spin_lock(&shmlock_user_lock);
memlock = inc_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
if ((memlock == LONG_MAX || memlock > lock_limit) && !capable(CAP_IPC_LOCK)) {
dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
goto out;
}
if (!get_ucounts(ucounts)) {
dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, locked);
allowed = 0;
goto out;
}
allowed = 1;
out:
spin_unlock(&shmlock_user_lock);
return allowed;
}
void user_shm_unlock(size_t size, struct ucounts *ucounts)
{
spin_lock(&shmlock_user_lock);
dec_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_MEMLOCK, (size + PAGE_SIZE - 1) >> PAGE_SHIFT);
spin_unlock(&shmlock_user_lock);
put_ucounts(ucounts);
}