Messages in this thread | | | Date | Fri, 15 Sep 2006 04:32:28 +0100 (BST) | From | Hugh Dickins <> | Subject | Re: Re: [RFC] PAGE_RW Should be added to PAGE_COPY ? |
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On Fri, 15 Sep 2006, Yingchao Zhou wrote: > > > >You want to mmap MAP_SHARED, which will use PAGE_SHARED instead, > >including the write bit, both before and after the mprotects. > >There should be no problem then: do you actually see a problem > >when MAP_SHARED is used? > It's ok to mmap MAP_SHARED. But is it not a normal way to malloc() a space and > then registered to NIC ?
Not that I know of. How would one register malloc()ed space to a NIC? Sorry, I may well be misunderstanding you.
> >> Adding PAGE_RW to PAGE_COPY will resolve this problem. > > > >No! That would give every user write access to shared files they > >should have no write access to. > I guess you refer to mmap a file MAP_READ|MAP_WRITE in MAP_PRIVATE way. > I think it is probably more logical to read the file data into an anoymous page and filled the pte with _PAGE_RW in the first time page-fault. It will probably reduce numbers of page fault interrupt.
do_no_page() does just that when its fault demands write access; but doesn't waste memory and time on copying when it's only a read access.
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