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</o:shapelayout></xml><![endif]--></head><body lang=KO link="#0563C1" vlink="#954F72"><div class=WordSection1><p class=MsoNormal><span lang=EN-US style='background:white'>Hello,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='background:white'>I was reading <a href="https://lwn.net/Articles/753027/">https://lwn.net/Articles/753027/</a> and it says<o:p></o:p></span></p><p class=MsoQuote><span lang=EN-US style='background:white'>Problems can arise when the kernel decides to perform writeback on some of the pages brought in with </span><tt><span lang=EN-US style='font-size:12.0pt;color:black;background:white'>get_user_pages()</span></tt><span lang=EN-US style='background:white'>. The writeback process will write-protect the pages so that user-space cannot modify them until writeback is complete, but it knows nothing about DMA operations started by the driver that called </span><tt><span lang=EN-US style='font-size:12.0pt;color:black;background:white'>get_user_pages()</span></tt><span lang=EN-US style='background:white'>; that I/O may still be ongoing. <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Does get_user_pages() start a DMA operation? If yes, is it for the user pages content? Or is it copying the page table?<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US>Or is the author talking about the DMA operation by the driver sometime after the get_user_pages operation?<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US>Chan Kim<o:p></o:p></span></p></div></body></html>