Re:AW: Re:puzzle about about page fault in sigma0 space

Thank you, Philipp. I got it.

Then , what about the first problem?
When accessing a virt address below 256M in sigma0 space, and a page fault occured.Then the page fault process will make phys : virt (1 : 1) mapping through map_sigma0() funtion.
Then it can access the phys address which is below 256M ? But these low 256M addresses is kernel used. And shouldn't be accessed by user thread directly. Or else the kernel data will be distroyed . 

Bob
 


"Philipp Kupferschmied" <[email protected]> wrote：
>
>The pager has to reply with a MapItem or GrantItem that specifies the fpage to be mapped.
>Such an item is interpreted by the kernel, which updates the corresponding page table and the mapping database. Processing of these typed items is performed by extended_transfer() in api/v4/ipcx.cc, which calls fpage_map() in generic/linear_ptab_walker.cc to update mapping information.
>More details about typed items, fpages, and L4 fault handling protocols can be found in the kernel reference manual [1]
>
>Cheers,
>Philipp
>
>[1] http://l4hq.org/docs/manuals/l4-x2-20061117.pdf