I think I'm finally getting the hang of this sort of thing, at least for lowmem x86 situations, so I'll try to answer. "Kirk True" <ktrue@movaris.com> writes: > Hi all, > > In <asm>/pgtable.h, it defines the following: > > 323 #define pmd_page(pmd) \ > 324 ((unsigned long) __va(pmd_val(pmd) & PAGE_MASK)) > > Why does it convert the physical address provided by pmd_val to a virtual > one? The addresses returned from pgd_offset and pmd_offset represent a > physical address, correct? I don't think so. > Then why the switch to a virtual address for the > pte_offset? > > Aren't these methods called from the kernel in the physical address space > rather than the linear/virtual address space? > > I'm confused, please help ;) In memory.c:free_one_pmd there's an example of how pmd_page is used. It yields a pointer to the struct page in the mem_map that corresponds to the page frame where the pmd is stored. That pointer is a virtual address. On lowmem x86, for kernel data, the relationship between a virtual address and a physical address is just the addition or subtraction of 0xC0000000. The __va macro just adds 0xC0000000 to the physical address. -- --Ed L Cashin | PGP public key: ecashin@uga.edu | http://noserose.net/e/pgp/ -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
