On Mon, Nov 3, 2014 at 6:45 AM, <Valdis.Kletnieks@xxxxxx> wrote: > On Sun, 02 Nov 2014 19:57:44 +0530, mind entropy said: >> In the copy_from_user when the user passes the virtual address is >> the address mapped in the kernel page tables? > > Actually, a large part of the reason for copy_from_user()'s existence is > to deal with the possibility that the page is *not* mapped at the moment > because it's been swapped out (at which point we need to schedule a read > operation for whatever backing store the page had (filesystem, swap, or > zero-page for a never-before-referenced page), wait for it to arrive, > and then nail it down so it doesn't leave out from under us before > we finish the copy from the page. Got this part. Now the mapping will be done in the kernel page table,correct? i.e. in the swapper_pg_dir and this would be what the MMU will use to walk, correct? In short when the memcpy is being done the page table will be the kernel pgd right? > > And of course, it's even *more* fun when the copy crosses a page boundary, > and one or both of the pages isn't resident.... > >> In the function there is >> a source is a user virtual address(<3GB) and the destination is the > > Only for 32-bit kernels. x86_64 has a different memory layout. _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
