Re: [RFC PATCH v2 2/3] mm: make pXd_addr_end() functions page-table entry aware

Christophe Leroy
2020-09-08T08:17:31Z

Le 08/09/2020 à 09:46, Alexander Gordeev a écrit :
> On Tue, Sep 08, 2020 at 07:14:38AM +0200, Christophe Leroy wrote:
>> You forgot arch/powerpc/mm/book3s64/subpage_prot.c it seems.
>
> Yes, and also two more sources :/
> arch/powerpc/mm/kasan/8xx.c
> arch/powerpc/mm/kasan/kasan_init_32.c
>
> But these two are not quite obvious wrt pgd_addr_end() used
> while traversing pmds. Could you please clarify a bit?
>
>
> diff --git a/arch/powerpc/mm/kasan/8xx.c b/arch/powerpc/mm/kasan/8xx.c
> index 2784224..89c5053 100644
> --- a/arch/powerpc/mm/kasan/8xx.c
> +++ b/arch/powerpc/mm/kasan/8xx.c
> @@ -15,8 +15,8 @@
> for (k_cur = k_start; k_cur != k_end; k_cur = k_next, pmd += 2, block += SZ_8M) {
> pte_basic_t *new;
>
> - k_next = pgd_addr_end(k_cur, k_end);
> - k_next = pgd_addr_end(k_next, k_end);
> + k_next = pmd_addr_end(k_cur, k_end);
> + k_next = pmd_addr_end(k_next, k_end);

No, I don't think so.
On powerpc32 we have only two levels, so pgd and pmd are more or less
the same.
But pmd_addr_end() as defined in include/asm-generic/pgtable-nopmd.h is
a no-op, so I don't think it will work.

It is likely that this function should iterate on pgd, then you get pmd
= pmd_offset(pud_offset(p4d_offset(pgd)));

> if ((void *)pmd_page_vaddr(*pmd) != kasan_early_shadow_pte)
> continue;
>
> diff --git a/arch/powerpc/mm/kasan/kasan_init_32.c b/arch/powerpc/mm/kasan/kasan_init_32.c
> index fb29404..3f7d6dc6 100644
> --- a/arch/powerpc/mm/kasan/kasan_init_32.c
> +++ b/arch/powerpc/mm/kasan/kasan_init_32.c
> @@ -38,7 +38,7 @@ int __init kasan_init_shadow_page_tables(unsigned long k_start, unsigned long k_
> for (k_cur = k_start; k_cur != k_end; k_cur = k_next, pmd++) {
> pte_t *new;
>
> - k_next = pgd_addr_end(k_cur, k_end);
> + k_next = pmd_addr_end(k_cur, k_end);

Same here I get, iterate on pgd then get pmd =
pmd_offset(pud_offset(p4d_offset(pgd)));

> if ((void *)pmd_page_vaddr(*pmd) != kasan_early_shadow_pte)
> continue;
>
> @@ -196,7 +196,7 @@ void __init kasan_early_init(void)
> kasan_populate_pte(kasan_early_shadow_pte, PAGE_KERNEL);
>
> do {
> - next = pgd_addr_end(addr, end);
> + next = pmd_addr_end(addr, end);
> pmd_populate_kernel(&init_mm, pmd, kasan_early_shadow_pte);
> } while (pmd++, addr = next, addr != end);
>
>

Christophe