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...@mail.gmail.com/
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.
