On Thu, 06 Jan 2005 19:12:15 +0100, Andi Kleen <[EMAIL PROTECTED]> wrote: > Yes, you should use get_user_pages() instead if you access real memory. > If you try to find hardware mappings using that there is no ready > function for you right now, although I guess it could be added.
drm_follow_page is used like this: offset = drm_follow_page(pt) | ((unsigned long) pt & ~PAGE_MASK); map = drm_lookup_map(offset, size, dev); if (map && map->type == _DRM_AGP) { vunmap(pt); return; } I think pt is a user space address. In DRM AGP memory is mapped into kernel and user space so the user space address is being converted into a kernel space one. The kernel space one is used to verify that the address is a valid mapping to AGP space, if so the page is unmapped. I didn't write this code so I'm not 100% sure of what is going on. On Thu, 06 Jan 2005 19:12:15 +0100, Andi Kleen <[EMAIL PROTECTED]> wrote: > Jon Smirl <[EMAIL PROTECTED]> writes: > > > The DRM driver contains this routine: > > > > drivers/char/drm/drm_memory.h > > > > static inline unsigned long > > drm_follow_page (void *vaddr) > > { > > pgd_t *pgd = pgd_offset_k((unsigned long) vaddr); > > pud_t *pud = pud_offset(pgd, (unsigned long) vaddr); > > pmd_t *pmd = pmd_offset(pud, (unsigned long) vaddr); > > pte_t *ptep = pte_offset_kernel(pmd, (unsigned long) vaddr); > > return pte_pfn(*ptep) << PAGE_SHIFT; > > } > > > > No other driver needs to chase the page table like this so there is > > probably some other way to achieve this. Can someone who knows more > > about the VM system tell me if there is a way to eliminate this code? > > Yes, you should use get_user_pages() instead if you access real memory. > If you try to find hardware mappings using that there is no ready > function for you right now, although I guess it could be added. > > The function is also not quite correct, it should already least take > the page_table_lock (depending on where you call it from) and check > p*_none() on each level. > > -Andi > -- Jon Smirl [EMAIL PROTECTED] ------------------------------------------------------- The SF.Net email is sponsored by: Beat the post-holiday blues Get a FREE limited edition SourceForge.net t-shirt from ThinkGeek. It's fun and FREE -- well, almost....http://www.thinkgeek.com/sfshirt -- _______________________________________________ Dri-devel mailing list Dri-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/dri-devel