Re: [PATCH] userfaultfd: snapshot VMA state across UFFDIO_COPY retry

[Heechan Kang]

Hello Mike,

I tested the vma_snapshot patch from this message on top of:

  6916d5703ddf ("Merge tag 'drm-fixes-2026-05-16' of https://gitlab.freedesktop.org/drm/kernel";)
  v7.1-rc3-362-g6916d5703ddf

I used my UFFDIO_COPY MAP_SHARED tmpfs -> MAP_PRIVATE tmpfs replacement
reproducer against a root-owned 0444 sparse tmpfs file.

Before the test:

  sha256: ad7facb2586fc6e966c004d7d1d16b024f5805ff7cb47c7a85dabd8b48892ca7

After running 30000 attempts as uid 1000, the reproducer reported:

  RESULT: not reproduced after 30000 attempts

The target file remained unchanged:

  sha256: ad7facb2586fc6e966c004d7d1d16b024f5805ff7cb47c7a85dabd8b48892ca7
  first 32 bytes remained zero

So this patch fixes the MAP_SHARED tmpfs -> MAP_PRIVATE tmpfs replacement
case I tested. I did not separately test the MAP_PRIVATE -> MAP_SHARED
panic case.

Tested-by: Heechan Kang <gganji11@xxxxxxxxx>

Thanks,
Heechan