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gup.c
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gup.c
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#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/err.h>
#include <linux/spinlock.h>
#include <linux/mm.h>
#include <linux/memremap.h>
#include <linux/pagemap.h>
#include <linux/rmap.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/sched/signal.h>
#include <linux/rwsem.h>
#include <linux/hugetlb.h>
#include <asm/mmu_context.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
#include "internal.h"
static struct page *no_page_table(struct vm_area_struct *vma,
unsigned int flags)
{
/*
* When core dumping an enormous anonymous area that nobody
* has touched so far, we don't want to allocate unnecessary pages or
* page tables. Return error instead of NULL to skip handle_mm_fault,
* then get_dump_page() will return NULL to leave a hole in the dump.
* But we can only make this optimization where a hole would surely
* be zero-filled if handle_mm_fault() actually did handle it.
*/
if ((flags & FOLL_DUMP) && (!vma->vm_ops || !vma->vm_ops->fault))
return ERR_PTR(-EFAULT);
return NULL;
}
static int follow_pfn_pte(struct vm_area_struct *vma, unsigned long address,
pte_t *pte, unsigned int flags)
{
/* No page to get reference */
if (flags & FOLL_GET)
return -EFAULT;
if (flags & FOLL_TOUCH) {
pte_t entry = *pte;
if (flags & FOLL_WRITE)
entry = pte_mkdirty(entry);
entry = pte_mkyoung(entry);
if (!pte_same(*pte, entry)) {
set_pte_at(vma->vm_mm, address, pte, entry);
update_mmu_cache(vma, address, pte);
}
}
/* Proper page table entry exists, but no corresponding struct page */
return -EEXIST;
}
/*
* FOLL_FORCE can write to even unwritable pte's, but only
* after we've gone through a COW cycle and they are dirty.
*/
static inline bool can_follow_write_pte(pte_t pte, unsigned int flags)
{
return pte_write(pte) ||
((flags & FOLL_FORCE) && (flags & FOLL_COW) && pte_dirty(pte));
}
static struct page *follow_page_pte(struct vm_area_struct *vma,
unsigned long address, pmd_t *pmd, unsigned int flags)
{
struct mm_struct *mm = vma->vm_mm;
struct dev_pagemap *pgmap = NULL;
struct page *page;
spinlock_t *ptl;
pte_t *ptep, pte;
retry:
if (unlikely(pmd_bad(*pmd)))
return no_page_table(vma, flags);
ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
pte = *ptep;
if (!pte_present(pte)) {
swp_entry_t entry;
/*
* KSM's break_ksm() relies upon recognizing a ksm page
* even while it is being migrated, so for that case we
* need migration_entry_wait().
*/
if (likely(!(flags & FOLL_MIGRATION)))
goto no_page;
if (pte_none(pte))
goto no_page;
entry = pte_to_swp_entry(pte);
if (!is_migration_entry(entry))
goto no_page;
pte_unmap_unlock(ptep, ptl);
migration_entry_wait(mm, pmd, address);
goto retry;
}
if ((flags & FOLL_NUMA) && pte_protnone(pte))
goto no_page;
if ((flags & FOLL_WRITE) && !can_follow_write_pte(pte, flags)) {
pte_unmap_unlock(ptep, ptl);
return NULL;
}
page = vm_normal_page(vma, address, pte);
if (!page && pte_devmap(pte) && (flags & FOLL_GET)) {
/*
* Only return device mapping pages in the FOLL_GET case since
* they are only valid while holding the pgmap reference.
*/
pgmap = get_dev_pagemap(pte_pfn(pte), NULL);
if (pgmap)
page = pte_page(pte);
else
goto no_page;
} else if (unlikely(!page)) {
if (flags & FOLL_DUMP) {
/* Avoid special (like zero) pages in core dumps */
page = ERR_PTR(-EFAULT);
goto out;
}
if (is_zero_pfn(pte_pfn(pte))) {
page = pte_page(pte);
} else {
int ret;
ret = follow_pfn_pte(vma, address, ptep, flags);
page = ERR_PTR(ret);
goto out;
}
}
if (flags & FOLL_SPLIT && PageTransCompound(page)) {
int ret;
get_page(page);
pte_unmap_unlock(ptep, ptl);
lock_page(page);
ret = split_huge_page(page);
unlock_page(page);
put_page(page);
if (ret)
return ERR_PTR(ret);
goto retry;
}
if (flags & FOLL_GET) {
get_page(page);
/* drop the pgmap reference now that we hold the page */
if (pgmap) {
put_dev_pagemap(pgmap);
pgmap = NULL;
}
}
if (flags & FOLL_TOUCH) {
if ((flags & FOLL_WRITE) &&
!pte_dirty(pte) && !PageDirty(page))
set_page_dirty(page);
/*
* pte_mkyoung() would be more correct here, but atomic care
* is needed to avoid losing the dirty bit: it is easier to use
* mark_page_accessed().
*/
mark_page_accessed(page);
}
if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
/* Do not mlock pte-mapped THP */
if (PageTransCompound(page))
goto out;
/*
* The preliminary mapping check is mainly to avoid the
* pointless overhead of lock_page on the ZERO_PAGE
* which might bounce very badly if there is contention.
*
* If the page is already locked, we don't need to
* handle it now - vmscan will handle it later if and
* when it attempts to reclaim the page.
*/
if (page->mapping && trylock_page(page)) {
lru_add_drain(); /* push cached pages to LRU */
/*
* Because we lock page here, and migration is
* blocked by the pte's page reference, and we
* know the page is still mapped, we don't even
* need to check for file-cache page truncation.
*/
mlock_vma_page(page);
unlock_page(page);
}
}
out:
pte_unmap_unlock(ptep, ptl);
return page;
no_page:
pte_unmap_unlock(ptep, ptl);
if (!pte_none(pte))
return NULL;
return no_page_table(vma, flags);
}
static struct page *follow_pmd_mask(struct vm_area_struct *vma,
unsigned long address, pud_t *pudp,
unsigned int flags, unsigned int *page_mask)
{
pmd_t *pmd, pmdval;
spinlock_t *ptl;
struct page *page;
struct mm_struct *mm = vma->vm_mm;
pmd = pmd_offset(pudp, address);
/*
* The READ_ONCE() will stabilize the pmdval in a register or
* on the stack so that it will stop changing under the code.
*/
pmdval = READ_ONCE(*pmd);
if (pmd_none(pmdval))
return no_page_table(vma, flags);
if (pmd_huge(pmdval) && vma->vm_flags & VM_HUGETLB) {
page = follow_huge_pmd(mm, address, pmd, flags);
if (page)
return page;
return no_page_table(vma, flags);
}
if (is_hugepd(__hugepd(pmd_val(pmdval)))) {
page = follow_huge_pd(vma, address,
__hugepd(pmd_val(pmdval)), flags,
PMD_SHIFT);
if (page)
return page;
return no_page_table(vma, flags);
}
retry:
if (!pmd_present(pmdval)) {
if (likely(!(flags & FOLL_MIGRATION)))
return no_page_table(vma, flags);
VM_BUG_ON(thp_migration_supported() &&
!is_pmd_migration_entry(pmdval));
if (is_pmd_migration_entry(pmdval))
pmd_migration_entry_wait(mm, pmd);
pmdval = READ_ONCE(*pmd);
/*
* MADV_DONTNEED may convert the pmd to null because
* mmap_sem is held in read mode
*/
if (pmd_none(pmdval))
return no_page_table(vma, flags);
goto retry;
}
if (pmd_devmap(pmdval)) {
ptl = pmd_lock(mm, pmd);
page = follow_devmap_pmd(vma, address, pmd, flags);
spin_unlock(ptl);
if (page)
return page;
}
if (likely(!pmd_trans_huge(pmdval)))
return follow_page_pte(vma, address, pmd, flags);
if ((flags & FOLL_NUMA) && pmd_protnone(pmdval))
return no_page_table(vma, flags);
retry_locked:
ptl = pmd_lock(mm, pmd);
if (unlikely(pmd_none(*pmd))) {
spin_unlock(ptl);
return no_page_table(vma, flags);
}
if (unlikely(!pmd_present(*pmd))) {
spin_unlock(ptl);
if (likely(!(flags & FOLL_MIGRATION)))
return no_page_table(vma, flags);
pmd_migration_entry_wait(mm, pmd);
goto retry_locked;
}
if (unlikely(!pmd_trans_huge(*pmd))) {
spin_unlock(ptl);
return follow_page_pte(vma, address, pmd, flags);
}
if (flags & FOLL_SPLIT) {
int ret;
page = pmd_page(*pmd);
if (is_huge_zero_page(page)) {
spin_unlock(ptl);
ret = 0;
split_huge_pmd(vma, pmd, address);
if (pmd_trans_unstable(pmd))
ret = -EBUSY;
} else {
get_page(page);
spin_unlock(ptl);
lock_page(page);
ret = split_huge_page(page);
unlock_page(page);
put_page(page);
if (pmd_none(*pmd))
return no_page_table(vma, flags);
}
return ret ? ERR_PTR(ret) :
follow_page_pte(vma, address, pmd, flags);
}
page = follow_trans_huge_pmd(vma, address, pmd, flags);
spin_unlock(ptl);
*page_mask = HPAGE_PMD_NR - 1;
return page;
}
static struct page *follow_pud_mask(struct vm_area_struct *vma,
unsigned long address, p4d_t *p4dp,
unsigned int flags, unsigned int *page_mask)
{
pud_t *pud;
spinlock_t *ptl;
struct page *page;
struct mm_struct *mm = vma->vm_mm;
pud = pud_offset(p4dp, address);
if (pud_none(*pud))
return no_page_table(vma, flags);
if (pud_huge(*pud) && vma->vm_flags & VM_HUGETLB) {
page = follow_huge_pud(mm, address, pud, flags);
if (page)
return page;
return no_page_table(vma, flags);
}
if (is_hugepd(__hugepd(pud_val(*pud)))) {
page = follow_huge_pd(vma, address,
__hugepd(pud_val(*pud)), flags,
PUD_SHIFT);
if (page)
return page;
return no_page_table(vma, flags);
}
if (pud_devmap(*pud)) {
ptl = pud_lock(mm, pud);
page = follow_devmap_pud(vma, address, pud, flags);
spin_unlock(ptl);
if (page)
return page;
}
if (unlikely(pud_bad(*pud)))
return no_page_table(vma, flags);
return follow_pmd_mask(vma, address, pud, flags, page_mask);
}
static struct page *follow_p4d_mask(struct vm_area_struct *vma,
unsigned long address, pgd_t *pgdp,
unsigned int flags, unsigned int *page_mask)
{
p4d_t *p4d;
struct page *page;
p4d = p4d_offset(pgdp, address);
if (p4d_none(*p4d))
return no_page_table(vma, flags);
BUILD_BUG_ON(p4d_huge(*p4d));
if (unlikely(p4d_bad(*p4d)))
return no_page_table(vma, flags);
if (is_hugepd(__hugepd(p4d_val(*p4d)))) {
page = follow_huge_pd(vma, address,
__hugepd(p4d_val(*p4d)), flags,
P4D_SHIFT);
if (page)
return page;
return no_page_table(vma, flags);
}
return follow_pud_mask(vma, address, p4d, flags, page_mask);
}
/**
* follow_page_mask - look up a page descriptor from a user-virtual address
* @vma: vm_area_struct mapping @address
* @address: virtual address to look up
* @flags: flags modifying lookup behaviour
* @page_mask: on output, *page_mask is set according to the size of the page
*
* @flags can have FOLL_ flags set, defined in <linux/mm.h>
*
* Returns the mapped (struct page *), %NULL if no mapping exists, or
* an error pointer if there is a mapping to something not represented
* by a page descriptor (see also vm_normal_page()).
*/
struct page *follow_page_mask(struct vm_area_struct *vma,
unsigned long address, unsigned int flags,
unsigned int *page_mask)
{
pgd_t *pgd;
struct page *page;
struct mm_struct *mm = vma->vm_mm;
*page_mask = 0;
/* make this handle hugepd */
page = follow_huge_addr(mm, address, flags & FOLL_WRITE);
if (!IS_ERR(page)) {
BUG_ON(flags & FOLL_GET);
return page;
}
pgd = pgd_offset(mm, address);
if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
return no_page_table(vma, flags);
if (pgd_huge(*pgd)) {
page = follow_huge_pgd(mm, address, pgd, flags);
if (page)
return page;
return no_page_table(vma, flags);
}
if (is_hugepd(__hugepd(pgd_val(*pgd)))) {
page = follow_huge_pd(vma, address,
__hugepd(pgd_val(*pgd)), flags,
PGDIR_SHIFT);
if (page)
return page;
return no_page_table(vma, flags);
}
return follow_p4d_mask(vma, address, pgd, flags, page_mask);
}
static int get_gate_page(struct mm_struct *mm, unsigned long address,
unsigned int gup_flags, struct vm_area_struct **vma,
struct page **page)
{
pgd_t *pgd;
p4d_t *p4d;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
int ret = -EFAULT;
/* user gate pages are read-only */
if (gup_flags & FOLL_WRITE)
return -EFAULT;
if (address > TASK_SIZE)
pgd = pgd_offset_k(address);
else
pgd = pgd_offset_gate(mm, address);
BUG_ON(pgd_none(*pgd));
p4d = p4d_offset(pgd, address);
BUG_ON(p4d_none(*p4d));
pud = pud_offset(p4d, address);
BUG_ON(pud_none(*pud));
pmd = pmd_offset(pud, address);
if (!pmd_present(*pmd))
return -EFAULT;
VM_BUG_ON(pmd_trans_huge(*pmd));
pte = pte_offset_map(pmd, address);
if (pte_none(*pte))
goto unmap;
*vma = get_gate_vma(mm);
if (!page)
goto out;
*page = vm_normal_page(*vma, address, *pte);
if (!*page) {
if ((gup_flags & FOLL_DUMP) || !is_zero_pfn(pte_pfn(*pte)))
goto unmap;
*page = pte_page(*pte);
/*
* This should never happen (a device public page in the gate
* area).
*/
if (is_device_public_page(*page))
goto unmap;
}
get_page(*page);
out:
ret = 0;
unmap:
pte_unmap(pte);
return ret;
}
/*
* mmap_sem must be held on entry. If @nonblocking != NULL and
* *@flags does not include FOLL_NOWAIT, the mmap_sem may be released.
* If it is, *@nonblocking will be set to 0 and -EBUSY returned.
*/
static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
unsigned long address, unsigned int *flags, int *nonblocking)
{
unsigned int fault_flags = 0;
int ret;
/* mlock all present pages, but do not fault in new pages */
if ((*flags & (FOLL_POPULATE | FOLL_MLOCK)) == FOLL_MLOCK)
return -ENOENT;
if (*flags & FOLL_WRITE)
fault_flags |= FAULT_FLAG_WRITE;
if (*flags & FOLL_REMOTE)
fault_flags |= FAULT_FLAG_REMOTE;
if (nonblocking)
fault_flags |= FAULT_FLAG_ALLOW_RETRY;
if (*flags & FOLL_NOWAIT)
fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
if (*flags & FOLL_TRIED) {
VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
fault_flags |= FAULT_FLAG_TRIED;
}
ret = handle_mm_fault(vma, address, fault_flags);
if (ret & VM_FAULT_ERROR) {
int err = vm_fault_to_errno(ret, *flags);
if (err)
return err;
BUG();
}
if (tsk) {
if (ret & VM_FAULT_MAJOR)
tsk->maj_flt++;
else
tsk->min_flt++;
}
if (ret & VM_FAULT_RETRY) {
if (nonblocking && !(fault_flags & FAULT_FLAG_RETRY_NOWAIT))
*nonblocking = 0;
return -EBUSY;
}
/*
* The VM_FAULT_WRITE bit tells us that do_wp_page has broken COW when
* necessary, even if maybe_mkwrite decided not to set pte_write. We
* can thus safely do subsequent page lookups as if they were reads.
* But only do so when looping for pte_write is futile: in some cases
* userspace may also be wanting to write to the gotten user page,
* which a read fault here might prevent (a readonly page might get
* reCOWed by userspace write).
*/
if ((ret & VM_FAULT_WRITE) && !(vma->vm_flags & VM_WRITE))
*flags |= FOLL_COW;
return 0;
}
static int check_vma_flags(struct vm_area_struct *vma, unsigned long gup_flags)
{
vm_flags_t vm_flags = vma->vm_flags;
int write = (gup_flags & FOLL_WRITE);
int foreign = (gup_flags & FOLL_REMOTE);
if (vm_flags & (VM_IO | VM_PFNMAP))
return -EFAULT;
if (gup_flags & FOLL_ANON && !vma_is_anonymous(vma))
return -EFAULT;
if (write) {
if (!(vm_flags & VM_WRITE)) {
if (!(gup_flags & FOLL_FORCE))
return -EFAULT;
/*
* We used to let the write,force case do COW in a
* VM_MAYWRITE VM_SHARED !VM_WRITE vma, so ptrace could
* set a breakpoint in a read-only mapping of an
* executable, without corrupting the file (yet only
* when that file had been opened for writing!).
* Anon pages in shared mappings are surprising: now
* just reject it.
*/
if (!is_cow_mapping(vm_flags))
return -EFAULT;
}
} else if (!(vm_flags & VM_READ)) {
if (!(gup_flags & FOLL_FORCE))
return -EFAULT;
/*
* Is there actually any vma we can reach here which does not
* have VM_MAYREAD set?
*/
if (!(vm_flags & VM_MAYREAD))
return -EFAULT;
}
/*
* gups are always data accesses, not instruction
* fetches, so execute=false here
*/
if (!arch_vma_access_permitted(vma, write, false, foreign))
return -EFAULT;
return 0;
}
/**
* __get_user_pages() - pin user pages in memory
* @tsk: task_struct of target task
* @mm: mm_struct of target mm
* @start: starting user address
* @nr_pages: number of pages from start to pin
* @gup_flags: flags modifying pin behaviour
* @pages: array that receives pointers to the pages pinned.
* Should be at least nr_pages long. Or NULL, if caller
* only intends to ensure the pages are faulted in.
* @vmas: array of pointers to vmas corresponding to each page.
* Or NULL if the caller does not require them.
* @nonblocking: whether waiting for disk IO or mmap_sem contention
*
* Returns number of pages pinned. This may be fewer than the number
* requested. If nr_pages is 0 or negative, returns 0. If no pages
* were pinned, returns -errno. Each page returned must be released
* with a put_page() call when it is finished with. vmas will only
* remain valid while mmap_sem is held.
*
* Must be called with mmap_sem held. It may be released. See below.
*
* __get_user_pages walks a process's page tables and takes a reference to
* each struct page that each user address corresponds to at a given
* instant. That is, it takes the page that would be accessed if a user
* thread accesses the given user virtual address at that instant.
*
* This does not guarantee that the page exists in the user mappings when
* __get_user_pages returns, and there may even be a completely different
* page there in some cases (eg. if mmapped pagecache has been invalidated
* and subsequently re faulted). However it does guarantee that the page
* won't be freed completely. And mostly callers simply care that the page
* contains data that was valid *at some point in time*. Typically, an IO
* or similar operation cannot guarantee anything stronger anyway because
* locks can't be held over the syscall boundary.
*
* If @gup_flags & FOLL_WRITE == 0, the page must not be written to. If
* the page is written to, set_page_dirty (or set_page_dirty_lock, as
* appropriate) must be called after the page is finished with, and
* before put_page is called.
*
* If @nonblocking != NULL, __get_user_pages will not wait for disk IO
* or mmap_sem contention, and if waiting is needed to pin all pages,
* *@nonblocking will be set to 0. Further, if @gup_flags does not
* include FOLL_NOWAIT, the mmap_sem will be released via up_read() in
* this case.
*
* A caller using such a combination of @nonblocking and @gup_flags
* must therefore hold the mmap_sem for reading only, and recognize
* when it's been released. Otherwise, it must be held for either
* reading or writing and will not be released.
*
* In most cases, get_user_pages or get_user_pages_fast should be used
* instead of __get_user_pages. __get_user_pages should be used only if
* you need some special @gup_flags.
*/
static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
unsigned long start, unsigned long nr_pages,
unsigned int gup_flags, struct page **pages,
struct vm_area_struct **vmas, int *nonblocking)
{
long i = 0;
unsigned int page_mask;
struct vm_area_struct *vma = NULL;
if (!nr_pages)
return 0;
VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
/*
* If FOLL_FORCE is set then do not force a full fault as the hinting
* fault information is unrelated to the reference behaviour of a task
* using the address space
*/
if (!(gup_flags & FOLL_FORCE))
gup_flags |= FOLL_NUMA;
do {
struct page *page;
unsigned int foll_flags = gup_flags;
unsigned int page_increm;
/* first iteration or cross vma bound */
if (!vma || start >= vma->vm_end) {
vma = find_extend_vma(mm, start);
if (!vma && in_gate_area(mm, start)) {
int ret;
ret = get_gate_page(mm, start & PAGE_MASK,
gup_flags, &vma,
pages ? &pages[i] : NULL);
if (ret)
return i ? : ret;
page_mask = 0;
goto next_page;
}
if (!vma || check_vma_flags(vma, gup_flags))
return i ? : -EFAULT;
if (is_vm_hugetlb_page(vma)) {
i = follow_hugetlb_page(mm, vma, pages, vmas,
&start, &nr_pages, i,
gup_flags, nonblocking);
continue;
}
}
retry:
/*
* If we have a pending SIGKILL, don't keep faulting pages and
* potentially allocating memory.
*/
if (unlikely(fatal_signal_pending(current)))
return i ? i : -ERESTARTSYS;
cond_resched();
page = follow_page_mask(vma, start, foll_flags, &page_mask);
if (!page) {
int ret;
ret = faultin_page(tsk, vma, start, &foll_flags,
nonblocking);
switch (ret) {
case 0:
goto retry;
case -EFAULT:
case -ENOMEM:
case -EHWPOISON:
return i ? i : ret;
case -EBUSY:
return i;
case -ENOENT:
goto next_page;
}
BUG();
} else if (PTR_ERR(page) == -EEXIST) {
/*
* Proper page table entry exists, but no corresponding
* struct page.
*/
goto next_page;
} else if (IS_ERR(page)) {
return i ? i : PTR_ERR(page);
}
if (pages) {
pages[i] = page;
flush_anon_page(vma, page, start);
flush_dcache_page(page);
page_mask = 0;
}
next_page:
if (vmas) {
vmas[i] = vma;
page_mask = 0;
}
page_increm = 1 + (~(start >> PAGE_SHIFT) & page_mask);
if (page_increm > nr_pages)
page_increm = nr_pages;
i += page_increm;
start += page_increm * PAGE_SIZE;
nr_pages -= page_increm;
} while (nr_pages);
return i;
}
static bool vma_permits_fault(struct vm_area_struct *vma,
unsigned int fault_flags)
{
bool write = !!(fault_flags & FAULT_FLAG_WRITE);
bool foreign = !!(fault_flags & FAULT_FLAG_REMOTE);
vm_flags_t vm_flags = write ? VM_WRITE : VM_READ;
if (!(vm_flags & vma->vm_flags))
return false;
/*
* The architecture might have a hardware protection
* mechanism other than read/write that can deny access.
*
* gup always represents data access, not instruction
* fetches, so execute=false here:
*/
if (!arch_vma_access_permitted(vma, write, false, foreign))
return false;
return true;
}
/*
* fixup_user_fault() - manually resolve a user page fault
* @tsk: the task_struct to use for page fault accounting, or
* NULL if faults are not to be recorded.
* @mm: mm_struct of target mm
* @address: user address
* @fault_flags:flags to pass down to handle_mm_fault()
* @unlocked: did we unlock the mmap_sem while retrying, maybe NULL if caller
* does not allow retry
*
* This is meant to be called in the specific scenario where for locking reasons
* we try to access user memory in atomic context (within a pagefault_disable()
* section), this returns -EFAULT, and we want to resolve the user fault before
* trying again.
*
* Typically this is meant to be used by the futex code.
*
* The main difference with get_user_pages() is that this function will
* unconditionally call handle_mm_fault() which will in turn perform all the
* necessary SW fixup of the dirty and young bits in the PTE, while
* get_user_pages() only guarantees to update these in the struct page.
*
* This is important for some architectures where those bits also gate the
* access permission to the page because they are maintained in software. On
* such architectures, gup() will not be enough to make a subsequent access
* succeed.
*
* This function will not return with an unlocked mmap_sem. So it has not the
* same semantics wrt the @mm->mmap_sem as does filemap_fault().
*/
int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
unsigned long address, unsigned int fault_flags,
bool *unlocked)
{
struct vm_area_struct *vma;
int ret, major = 0;
if (unlocked)
fault_flags |= FAULT_FLAG_ALLOW_RETRY;
retry:
vma = find_extend_vma(mm, address);
if (!vma || address < vma->vm_start)
return -EFAULT;
if (!vma_permits_fault(vma, fault_flags))
return -EFAULT;
ret = handle_mm_fault(vma, address, fault_flags);
major |= ret & VM_FAULT_MAJOR;
if (ret & VM_FAULT_ERROR) {
int err = vm_fault_to_errno(ret, 0);
if (err)
return err;
BUG();
}
if (ret & VM_FAULT_RETRY) {
down_read(&mm->mmap_sem);
if (!(fault_flags & FAULT_FLAG_TRIED)) {
*unlocked = true;
fault_flags &= ~FAULT_FLAG_ALLOW_RETRY;
fault_flags |= FAULT_FLAG_TRIED;
goto retry;
}
}
if (tsk) {
if (major)
tsk->maj_flt++;
else
tsk->min_flt++;
}
return 0;
}
EXPORT_SYMBOL_GPL(fixup_user_fault);
static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
struct mm_struct *mm,
unsigned long start,
unsigned long nr_pages,
struct page **pages,
struct vm_area_struct **vmas,
int *locked,
unsigned int flags)
{
long ret, pages_done;
bool lock_dropped;
if (locked) {
/* if VM_FAULT_RETRY can be returned, vmas become invalid */
BUG_ON(vmas);
/* check caller initialized locked */
BUG_ON(*locked != 1);
}
if (pages)
flags |= FOLL_GET;
pages_done = 0;
lock_dropped = false;
for (;;) {
ret = __get_user_pages(tsk, mm, start, nr_pages, flags, pages,
vmas, locked);
if (!locked)
/* VM_FAULT_RETRY couldn't trigger, bypass */
return ret;
/* VM_FAULT_RETRY cannot return errors */
if (!*locked) {
BUG_ON(ret < 0);
BUG_ON(ret >= nr_pages);
}
if (!pages)
/* If it's a prefault don't insist harder */
return ret;
if (ret > 0) {
nr_pages -= ret;
pages_done += ret;
if (!nr_pages)
break;
}
if (*locked) {
/*
* VM_FAULT_RETRY didn't trigger or it was a
* FOLL_NOWAIT.
*/
if (!pages_done)
pages_done = ret;
break;
}
/* VM_FAULT_RETRY triggered, so seek to the faulting offset */
pages += ret;
start += ret << PAGE_SHIFT;
/*
* Repeat on the address that fired VM_FAULT_RETRY
* without FAULT_FLAG_ALLOW_RETRY but with
* FAULT_FLAG_TRIED.
*/
*locked = 1;
lock_dropped = true;
down_read(&mm->mmap_sem);
ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
pages, NULL, NULL);
if (ret != 1) {
BUG_ON(ret > 1);
if (!pages_done)
pages_done = ret;
break;
}
nr_pages--;
pages_done++;
if (!nr_pages)
break;
pages++;
start += PAGE_SIZE;
}
if (lock_dropped && *locked) {
/*
* We must let the caller know we temporarily dropped the lock
* and so the critical section protected by it was lost.
*/
up_read(&mm->mmap_sem);
*locked = 0;
}
return pages_done;
}
/*
* We can leverage the VM_FAULT_RETRY functionality in the page fault
* paths better by using either get_user_pages_locked() or
* get_user_pages_unlocked().
*
* get_user_pages_locked() is suitable to replace the form:
*
* down_read(&mm->mmap_sem);
* do_something()
* get_user_pages(tsk, mm, ..., pages, NULL);
* up_read(&mm->mmap_sem);
*
* to:
*
* int locked = 1;
* down_read(&mm->mmap_sem);
* do_something()
* get_user_pages_locked(tsk, mm, ..., pages, &locked);
* if (locked)
* up_read(&mm->mmap_sem);
*/
long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
unsigned int gup_flags, struct page **pages,
int *locked)
{
return __get_user_pages_locked(current, current->mm, start, nr_pages,
pages, NULL, locked,
gup_flags | FOLL_TOUCH);
}
EXPORT_SYMBOL(get_user_pages_locked);
/*
* get_user_pages_unlocked() is suitable to replace the form:
*
* down_read(&mm->mmap_sem);
* get_user_pages(tsk, mm, ..., pages, NULL);
* up_read(&mm->mmap_sem);
*
* with:
*
* get_user_pages_unlocked(tsk, mm, ..., pages);
*
* It is functionally equivalent to get_user_pages_fast so