I don't seem to have gotten patches 0-2,7 for some reason; I'll try and
dig them out of the LKML folder.
On Sat, Nov 10, 2018 at 03:17:27PM -0800, Nadav Amit wrote:
> +void __init poking_init(void)
> +{
> + spinlock_t *ptl;
> + pte_t *ptep;
> +
> + poking_mm = copy_init_mm();
> + if (!poking_mm) {
> + pr_err("x86/mm: error setting a separate poking address space");
> + return;
> + }
> +
> + /*
> + * Randomize the poking address, but make sure that the following page
> + * will be mapped at the same PMD. We need 2 pages, so find space for 3,
> + * and adjust the address if the PMD ends after the first one.
> + */
> + poking_addr = TASK_UNMAPPED_BASE +
> + (kaslr_get_random_long("Poking") & PAGE_MASK) %
> + (TASK_SIZE - TASK_UNMAPPED_BASE - 3 * PAGE_SIZE);
> +
> + if (((poking_addr + PAGE_SIZE) & ~PMD_MASK) == 0)
> + poking_addr += PAGE_SIZE;
> +
> + /*
> + * We need to trigger the allocation of the page-tables that will be
> + * needed for poking now. Later, poking may be performed in an atomic
> + * section, which might cause allocation to fail.
> + */
> + ptep = get_locked_pte(poking_mm, poking_addr, &ptl);
> + if (!WARN_ON(!ptep))
> + pte_unmap_unlock(ptep, ptl);
> +}
The difference in how we deal with -ENOMEM here is weird. I think we
have a _lot_ of code that simply hard assumes we don't fail memory alloc
on init.
I for instance would not mind to simply remove both branches and let the
kernel crash and burn if we ever fail here.
