On Thu, Jan 27, 2005 at 04:52:54AM -0800, William Lee Irwin III wrote: >> FIRST_USER_PGD_NR is a matter of killing the entire box dead where it >> exists, not any kind of process' preference. Userspace should be >> prevented from setting up vmas below FIRST_USER_PGD_NR.
On Thu, Jan 27, 2005 at 02:25:00PM +0000, Russell King wrote: > No it should not. The PGD index is FAR to coarse to use - each PGD on > ARM maps 1MB of virtual address space. Userspace text starts at 32K. > The protection against mmap() MAP_FIXED fiddling with the first page is > handled by the arch-specific mmap() wrappers, so generic code doesn't > have to worry about it. > What generic code _does_ have to worry about is: > > (a) not removing the very first page. > (b) not removing the very first pointer to the 2nd level table in the > 1st level tables. > and that is all. Maybe FIRST_USER_PGD_NR was a bad way of achieving > this, but in the instance of the VM upon which it was originally > implemented (somewhere between 2.2 and 2.4), it was deemed (by others > iirc) to be the best way of achieving it at the time. The only claim above is the effect of clobbering virtual page 0 and referring to this phenomenon by the macro. I was rather careful not to claim a specific lower boundary to the address space. -- wli - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
