Thanks Jeff. Solved my problem. Below is my further investigation to support Jeff's idea.
The size of a Page Table (not a single entry) at any level is exactly 1 page. 2 level: 10+10+12. linear address will assign 10 bits for Page Directory and 10 bits for Page Table, and thus each Page Table will have 2^10=1K entries, and each entry has 4 Bytes. That's 4K in total, the same to the size of one page. 3 level for ia64: the paging mechanism is 9+9+9+12. Each level will have 2^9=512 entries. and 8 Bytes for each entry. Thus take up 512*8=4K in total. Again is the size of one page. On 11/09/2013 09:56 AM, Jeff Haran wrote: > I believe the directory entries are all exactly 1 page and page aligned. The > number of bits of address space each level covers is derived from this and > the size of each page table entry which has to be big enough to contain > whatever the physical address size is on the CPU. Take a look at the various > definitions of PGDIR_SHIFT and PAGE_SHIFT in the various arch directories. > Page tables on 32 bit machines can contain 1K 32 bit entries (4KB) but on 64 > bit machines they only contain 512 64 bit entries (still 4KB). > > Jeff Haran > > From: kernelnewbies-boun...@kernelnewbies.org > [mailto:kernelnewbies-boun...@kernelnewbies.org] On Behalf Of Mark Wallace > Sent: Friday, November 08, 2013 5:38 PM > To: kernelnewbies@kernelnewbies.org > Subject: Physical address of Page Table Entries > > Hi all, > > Question: > When we use 2 level paging(Directory+Table+Offset), does the page table > entries have to be put exactly on the beginning of a page frame? > > Description: > The format of Page Directory and Page Table are the same. And they all > contain 20 bits as a pointer to the next level entries. > > For Page Table entry, I understand that 20 bits is enough because page frames > are 4k aligned. But for Page Directory entry, the 20 bits should be the > address of a Page Table, that means the physical address of a Page Table > entry should be 4k aligned too. And thus they may only exist at the beginning > of a page frame. > > Is this right or am I missing something? > > Thanks. _______________________________________________ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
