Re: RE: [RFC] PAGE_RW Should be added to PAGE_COPY ?

[Yingchao Zhou]

I think it's OK to lock the page for the NIC driver. But I think it is an OS flaw to 
clear the _PAGE_RW bit for ptes in the mprotected space. If the _PAGE_RW is set, it 
should not get to do_wp_page.

Best regards
>Your analysis is correct. But locking a page to avoid swap has different
>meaning with page locked (TestSetPageLocked()). Looks you missed this.
>
>Thanks,
>Shaohua
>-----Original Message-----
>From: linux-kernel-owner@xxxxxxxxxxxxxxx
>[mailto:linux-kernel-owner@xxxxxxxxxxxxxxx] On Behalf Of Yingchao Zhou
>Sent: Wednesday, September 13, 2006 10:03 PM
>To: linux-kernel
>Cc: akpm; alan; zxc
>Subject: [RFC] PAGE_RW Should be added to PAGE_COPY ?
>
>
>     The current kernel set PAGE_COPY without write bit. This will cause
>intermittent non-cosistent data for user-level network drivers such as
>Infiniband, Quadrics and Myrinet. Which has also be mentioned by Costin
>Iancu in the paper "HUNTing the Overlap " (PACT'05).
>    An example of such phenomena is the following sequences: 
>	register a memory space BUFF for receive message, 
>	receive message,
>	call mprotect(...PROT_NONE...) and
>mprotect(...PROT_READ|PROT_WRITE) one by one, 	
>	write into BUFF, 
>	then receive again.      
>    The second time received data will perhaps not be the data sent by
>the peer machine but the data written by itself in the 4th step.
>
>     The reson is that :
>     1) User-level network driver locks phy pages when memory space is
>registered;
>........

___________________________________________________
_      Yingchao Zhou                              _
_      ICT, CAS                                   _
_      (86)010-62601009                           _
___________________________________________________



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