OrgACRN
/
acrn-kernel
mirror of https://github.com/projectacrn/acrn-kernel.git
1
0
Fork 0
Code Issues Releases Wiki Activity

mm: enable maple tree RCU mode by default 

Use the maple tree in RCU mode for VMA tracking.

The maple tree tracks the stack and is able to update the pivot
(lower/upper boundary) in-place to allow the page fault handler to write
to the tree while holding just the mmap read lock.  This is safe as the
writes to the stack have a guard VMA which ensures there will always be a
NULL in the direction of the growth and thus will only update a pivot.

It is possible, but not recommended, to have VMAs that grow up/down
without guard VMAs.  syzbot has constructed a testcase which sets up a VMA
to grow and consume the empty space.  Overwriting the entire NULL entry
causes the tree to be altered in a way that is not safe for concurrent
readers; the readers may see a node being rewritten or one that does not
match the maple state they are using.

Enabling RCU mode allows the concurrent readers to see a stable node and
will return the expected result.

[Liam.Howlett@Oracle.com: we don't need to free the nodes with RCU[
Link: https://lore.kernel.org/linux-mm/000000000000b0a65805f663ace6@google.com/
Link: https://lkml.kernel.org/r/20230227173632.3292573-9-surenb@google.com
Fixes: d4af56c5c7 ("mm: start tracking VMAs with maple tree")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reported-by: syzbot+8d95422d3537159ca390@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Liam R. Howlett 2023-02-27 09:36:07 -08:00 committed by Andrew Morton
parent 790e1fa86b
commit 3dd4432549
3 changed files with 7 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/mm_types.h
View File

@ -774,7 +774,8 @@ struct mm_struct {
unsigned long cpu_bitmap[]; unsigned long cpu_bitmap[];
}; };
#define MM_MT_FLAGS (MT_FLAGS_ALLOC_RANGE | MT_FLAGS_LOCK_EXTERN) #define MM_MT_FLAGS (MT_FLAGS_ALLOC_RANGE | MT_FLAGS_LOCK_EXTERN | \
MT_FLAGS_USE_RCU)
extern struct mm_struct init_mm; extern struct mm_struct init_mm;
/* Pointer magic because the dynamic array size confuses some compilers. */ /* Pointer magic because the dynamic array size confuses some compilers. */

3
kernel/fork.c
View File

@ -617,6 +617,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
if (retval) if (retval)
goto out; goto out;
mt_clear_in_rcu(vmi.mas.tree);
for_each_vma(old_vmi, mpnt) { for_each_vma(old_vmi, mpnt) {
struct file *file; struct file *file;
@ -700,6 +701,8 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
retval = arch_dup_mmap(oldmm, mm); retval = arch_dup_mmap(oldmm, mm);
loop_out: loop_out:
vma_iter_free(&vmi); vma_iter_free(&vmi);
if (!retval)
mt_set_in_rcu(vmi.mas.tree);
out: out:
mmap_write_unlock(mm); mmap_write_unlock(mm);
flush_tlb_mm(oldmm); flush_tlb_mm(oldmm);

3
mm/mmap.c
View File

@ -2277,7 +2277,7 @@ do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
int count = 0; int count = 0;
int error = -ENOMEM; int error = -ENOMEM;
MA_STATE(mas_detach, &mt_detach, 0, 0); MA_STATE(mas_detach, &mt_detach, 0, 0);
mt_init_flags(&mt_detach, MT_FLAGS_LOCK_EXTERN); mt_init_flags(&mt_detach, vmi->mas.tree->ma_flags & MT_FLAGS_LOCK_MASK);
mt_set_external_lock(&mt_detach, &mm->mmap_lock); mt_set_external_lock(&mt_detach, &mm->mmap_lock);
/* /*
@ -3037,6 +3037,7 @@ void exit_mmap(struct mm_struct *mm)
*/ */
set_bit(MMF_OOM_SKIP, &mm->flags); set_bit(MMF_OOM_SKIP, &mm->flags);
mmap_write_lock(mm); mmap_write_lock(mm);
mt_clear_in_rcu(&mm->mm_mt);
free_pgtables(&tlb, &mm->mm_mt, vma, FIRST_USER_ADDRESS, free_pgtables(&tlb, &mm->mm_mt, vma, FIRST_USER_ADDRESS,
USER_PGTABLES_CEILING); USER_PGTABLES_CEILING);
tlb_finish_mmu(&tlb); tlb_finish_mmu(&tlb);