mm: fix unmap_mapping_range high bits shift bug

The bug happens when highest bit of holebegin is 1, suppose holebegin is
0x8000000111111000, after shift, hba would be 0xfff8000000111111, then
vma_interval_tree_foreach would look it up fail or leads to the wrong
result.

error call seq e.g.:
- mmap(..., offset=0x8000000111111000)
  |- syscall(mmap, ... unsigned long, off):
     |- ksys_mmap_pgoff( ... , off >> PAGE_SHIFT);

  here pgoff is correctly shifted to 0x8000000111111,
  but pass 0x8000000111111000 as holebegin to unmap
  would then cause terrible result, as shown below:

- unmap_mapping_range(..., loff_t const holebegin)
  |- pgoff_t hba = holebegin >> PAGE_SHIFT;
          /* hba = 0xfff8000000111111 unexpectedly */

The issue happens in Heterogeneous computing, where the device(e.g. 
gpu) and host share the same virtual address space.

A simple workflow pattern which hit the issue is:
        /* host */
    1. userspace first mmap a file backed VA range with specified offset.
                        e.g. (offset=0x800..., mmap return: va_a)
    2. write some data to the corresponding sys page
                         e.g. (va_a = 0xAABB)
        /* device */
    3. gpu workload touches VA, triggers gpu fault and notify the host.
        /* host */
    4. reviced gpu fault notification, then it will:
            4.1 unmap host pages and also takes care of cpu tlb
                  (use unmap_mapping_range with offset=0x800...)
            4.2 migrate sys page to device
            4.3 setup device page table and resolve device fault.
        /* device */
    5. gpu workload continued, it accessed va_a and got 0xAABB.
    6. gpu workload continued, it wrote 0xBBCC to va_a.
        /* host */
    7. userspace access va_a, as expected, it will:
            7.1 trigger cpu vm fault.
            7.2 driver handling fault to migrate gpu local page to host.
    8. userspace then could correctly get 0xBBCC from va_a
    9. done

But in step 4.1, if we hit the bug this patch mentioned, then userspace
would never trigger cpu fault, and still get the old value: 0xAABB.

Making holebegin unsigned first fixes the bug.

Link: https://lkml.kernel.org/r/20231220052839.26970-1-jiajun.xie.sh@gmail.com
Signed-off-by: Jiajun Xie <jiajun.xie.sh@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

0 files changed, 0 insertions, 0 deletions