On Thu, Jul 25, 2019 at 12:25:23PM +0530, Anshuman Khandual wrote:
> This adds a test module which will validate architecture page table helpers
> and accessors regarding compliance with generic MM semantics expectations.
> This will help various architectures in validating changes to the existing
> page table helpers or addition of new ones.
I think this is a really good idea.
> lib/Kconfig.debug | 14 +++
> lib/Makefile | 1 +
> lib/test_arch_pgtable.c | 290
> ++++++++++++++++++++++++++++++++++++++++++++++++
Is this the right place for it? I worry that lib/ is going to get overloaded
with test code, and this feels more like mm/ test code.
> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE
> +static void pmd_basic_tests(void)
> +{
> + pmd_t pmd;
> +
> + pmd = mk_pmd(page, prot);
But 'page' isn't necessarily PMD-aligned. I don't think we can rely on
architectures doing the right thing if asked to make a PMD for a randomly
aligned page.
How about finding the physical address of something like kernel_init(),
and using the corresponding pte/pmd/pud/p4d/pgd that encompasses that
address? It's also better to pass in the pfn/page rather than using global
variables to communicate to the test functions.
> + /*
> + * A huge page does not point to next level page table
> + * entry. Hence this must qualify as pmd_bad().
> + */
> + WARN_ON(!pmd_bad(pmd_mkhuge(pmd)));
I didn't know that rule. This is helpful because it gives us somewhere
to document all these tricksy little rules.
> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> +static void pud_basic_tests(void)
Is this the right ifdef?
