Hello,

Thank you revisit this. But as far as my remember is correct, this issue is NOT
unaligned access issue. It's just get_user_pages(_fast) vs fork race issue. i.e.
DIRECT_IO w/ multi thread process should not use fork().

The problem is, fork (and its COW logic) assume new access makes cow break,
But page table protection can't detect a DMA write. Therefore DIO may override
shared page data.

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