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fsnotify: generate pre-content permission event on page fault

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FS_PRE_ACCESS will be generated on page fault depending on the faulting
method. This pre-content event is meant to be used by hierarchical storage
managers that want to fill in the file content on first read access.

Export a simple helper that file systems that have their own ->fault()
will use, and have a more complicated helper to be do fancy things in
filemap_fault.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/aa56c50ce81b1fd18d7f5d71dd2dfced5eba9687.1731684329.git.josef@toxicpanda.com
This commit is contained in:
Josef Bacik 2024-11-15 10:30:29 -05:00 committed by Jan Kara
parent 20bf82a898
commit 8392bc2ff8
3 changed files with 82 additions and 0 deletions
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1
include/linux/mm.h
View File

@ -3420,6 +3420,7 @@ extern vm_fault_t filemap_fault(struct vm_fault *vmf);
extern vm_fault_t filemap_map_pages(struct vm_fault *vmf,
pgoff_t start_pgoff, pgoff_t end_pgoff);
extern vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf);
extern vm_fault_t filemap_fsnotify_fault(struct vm_fault *vmf);
extern unsigned long stack_guard_gap;
/* Generic expand stack which grows the stack according to GROWS{UP,DOWN} */

74
mm/filemap.c
View File

@ -47,6 +47,7 @@
#include <linux/splice.h>
#include <linux/rcupdate_wait.h>
#include <linux/sched/mm.h>
#include <linux/fsnotify.h>
#include <asm/pgalloc.h>
#include <asm/tlbflush.h>
#include "internal.h"
@ -3288,6 +3289,48 @@ static vm_fault_t filemap_fault_recheck_pte_none(struct vm_fault *vmf)
return ret;
}
/**
* filemap_fsnotify_fault - maybe emit a pre-content event.
* @vmf: struct vm_fault containing details of the fault.
*
* If we have a pre-content watch on this file we will emit an event for this
* range. If we return anything the fault caller should return immediately, we
* will return VM_FAULT_RETRY if we had to emit an event, which will trigger the
* fault again and then the fault handler will run the second time through.
*
* Return: a bitwise-OR of %VM_FAULT_ codes, 0 if nothing happened.
*/
vm_fault_t filemap_fsnotify_fault(struct vm_fault *vmf)
{
struct file *fpin = NULL;
int mask = (vmf->flags & FAULT_FLAG_WRITE) ? MAY_WRITE : MAY_ACCESS;
loff_t pos = vmf->pgoff >> PAGE_SHIFT;
size_t count = PAGE_SIZE;
int err;
/*
* We already did this and now we're retrying with everything locked,
* don't emit the event and continue.
*/
if (vmf->flags & FAULT_FLAG_TRIED)
return 0;
/* No watches, we're done. */
if (likely(!FMODE_FSNOTIFY_HSM(vmf->vma->vm_file->f_mode)))
return 0;
fpin = maybe_unlock_mmap_for_io(vmf, fpin);
if (!fpin)
return VM_FAULT_SIGBUS;
err = fsnotify_file_area_perm(fpin, mask, &pos, count);
fput(fpin);
if (err)
return VM_FAULT_SIGBUS;
return VM_FAULT_RETRY;
}
EXPORT_SYMBOL_GPL(filemap_fsnotify_fault);
/**
* filemap_fault - read in file data for page fault handling
* @vmf: struct vm_fault containing details of the fault
@ -3391,6 +3434,37 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
* or because readahead was otherwise unable to retrieve it.
*/
if (unlikely(!folio_test_uptodate(folio))) {
/*
* If this is a precontent file we have can now emit an event to
* try and populate the folio.
*/
if (!(vmf->flags & FAULT_FLAG_TRIED) &&
unlikely(FMODE_FSNOTIFY_HSM(file->f_mode))) {
loff_t pos = folio_pos(folio);
size_t count = folio_size(folio);
/* We're NOWAIT, we have to retry. */
if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) {
folio_unlock(folio);
goto out_retry;
}
if (mapping_locked)
filemap_invalidate_unlock_shared(mapping);
mapping_locked = false;
folio_unlock(folio);
fpin = maybe_unlock_mmap_for_io(vmf, fpin);
if (!fpin)
goto out_retry;
error = fsnotify_file_area_perm(fpin, MAY_ACCESS, &pos,
count);
if (error)
ret = VM_FAULT_SIGBUS;
goto out_retry;
}
/*
* If the invalidate lock is not held, the folio was in cache
* and uptodate and now it is not. Strange but possible since we

7
mm/nommu.c
View File

@ -1613,6 +1613,13 @@ int remap_vmalloc_range(struct vm_area_struct *vma, void *addr,
}
EXPORT_SYMBOL(remap_vmalloc_range);
vm_fault_t filemap_fsnotify_fault(struct vm_fault *vmf)
{
BUG();
return 0;
}
EXPORT_SYMBOL_GPL(filemap_fsnotify_fault);
vm_fault_t filemap_fault(struct vm_fault *vmf)
{
BUG();