The quilt patch titled Subject: mm: fix unmap_mapping_range high bits shift bug has been removed from the -mm tree. Its filename was mm-fix-unmap_mapping_range-high-bits-shift-bug.patch
This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------ From: Jiajun Xie jiajun.xie.sh@gmail.com Subject: mm: fix unmap_mapping_range high bits shift bug Date: Wed, 20 Dec 2023 13:28:39 +0800
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 ---
mm/memory.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
--- a/mm/memory.c~mm-fix-unmap_mapping_range-high-bits-shift-bug +++ a/mm/memory.c @@ -3624,8 +3624,8 @@ EXPORT_SYMBOL_GPL(unmap_mapping_pages); void unmap_mapping_range(struct address_space *mapping, loff_t const holebegin, loff_t const holelen, int even_cows) { - pgoff_t hba = holebegin >> PAGE_SHIFT; - pgoff_t hlen = (holelen + PAGE_SIZE - 1) >> PAGE_SHIFT; + pgoff_t hba = (pgoff_t)(holebegin) >> PAGE_SHIFT; + pgoff_t hlen = ((pgoff_t)(holelen) + PAGE_SIZE - 1) >> PAGE_SHIFT;
/* Check for overflow. */ if (sizeof(holelen) > sizeof(hlen)) { _
Patches currently in -mm which might be from jiajun.xie.sh@gmail.com are