Hi Yongting,

On 8/18/25 2:44 AM, Yongting Lin wrote:

Thank you! Anthony.

Yep, I checked the comments in arch/mm/x86/fault.c file which says as your advices in previous email.

I changed my code in kernel 5.5 as below:

    if (unlikely(is_shared_vma) && ((fault & VM_FAULT_RETRY) &&
        (flags & FAULT_FLAG_ALLOW_RETRY) || fault_signal_pending(fault, regs)))
            mmap_read_unlock(mm);

BTW: I wrote some selftests in my github repostory, which perform the basic function of mshare, and I will write some complicated cases to support the new functions or defect found in mshare. For example, once you support mshare as a VMA in KVM (just as the defeat viewed by Jann Horn), I will add extra test cases to verify its correctiness for this scenario.

This is great! I'll take a look at them in more detail. I just sent out an updated series.

From Jann Horn's review: https://lore.kernel.org/all/CAG48ez3cUZf+xOtP6UkkS2-CmOeo+3K5pvny0AFL_XBkHh5...

My new series does not yet have support for mmu notifiers. It's something I'm working on, but there are key issues to overcome. One is that I need to update the implementation of mm_take_all_locks() to also carefully take all locks in any mapped mshare regions. The other is that passing through mmu notifier calls for arch_invalidate_secondary_tlbs callbacks is especially tricky because the callback is not allowed to sleep due to holding a ptl spin lock.

Currently, I put my selftest in my github repostory, and you could retrieve it as below:

 git remote add yongting-mshare-selftests https://github.com/ivanalgo/linux-kernel-develop/
 git fetch yongting-mshare-selftests dev-mshare-v2-selftest-v1
 git cherry-pick a64f2ff6497d13c09badc0fc68c44d9995bc2fef

At this stage, I am not sure what is the best way to proceed:

• Should I send them as part of your next version (v3)?
• Or should I post them separately as [RFC PATCH] for early review?

Please let me know your preference and any sugestion is welcome. I am happy to rebase and resend in the format that works best for the community.

I may have more feedback once I take look. I suggest starting by updating them to work with the series I just sent out.

Thanks, Anthony

Thanks Yongting

...

Anthony

...

As a result, needs to release vma->vm_mm.mmap_lock as well.

So it is supposed to be like below:

• fault = handle_mm_fault(vma, address, flags, regs);

• fault = handle_mm_fault(vma, addr, flags, regs);
• if (unlikely(is_shared_vma) && ((fault & VM_FAULT_COMPLETED) ||

•    (fault & VM_FAULT_RETRY) || fault_signal_pending(fault, regs))) {
  

•    mmap_read_unlock(vma->vm_mm);
  

•    mmap_read_unlock(mm);
  

• }

...

     if (fault_signal_pending(fault, regs)) {
       /*

@@ -1413,6 +1446,8 @@ void do_user_addr_fault(struct pt_regs *regs, goto retry; }

• if (unlikely(is_shared_vma))

•    mmap_read_unlock(vma->vm_mm);
   mmap_read_unlock(mm);
  

  done: if (likely(!(fault & VM_FAULT_ERROR)))

diff --git a/mm/Kconfig b/mm/Kconfig index e6c90db83d01..8a5a159457f2 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1344,7 +1344,7 @@ config PT_RECLAIM config MSHARE bool "Mshare"

• depends on MMU

• depends on MMU && ARCH_SUPPORTS_MSHARE help Enable msharefs: A ram-based filesystem that allows multiple processes to share page table entries for shared pages. A file

Yongting Lin.