On Mon, May 27, 2024 at 03:30:12PM +0200, Christophe Leroy wrote:
> On book3s/64, the only user of hugepd is hash in 4k mode.
>
> All other setups (hash-64, radix-4, radix-64) use leaf PMD/PUD.
>
> Rework hash-4k to use contiguous PMD and PUD instead.
>
> In that setup there are only two huge page sizes: 16M and 16G.
>
> 16M sits at PMD level and 16G at PUD level.
On 4k mode, PMD_SIZE is 2MB and PUD_SIZE is 256MB, right?
> +static inline unsigned long hash__pte_update(struct mm_struct *mm,
> + unsigned long addr,
> + pte_t *ptep, unsigned long clr,
> + unsigned long set,
> + int huge)
> +{
> + unsigned long old;
> +
> + old = hash__pte_update_one(ptep, clr, set);
> +
> + if (IS_ENABLED(CONFIG_PPC_4K_PAGES) && huge) {
> + unsigned int psize = get_slice_psize(mm, addr);
> + int nb, i;
> +
> + if (psize == MMU_PAGE_16M)
> + nb = SZ_16M / PMD_SIZE;
> + else if (psize == MMU_PAGE_16G)
> + nb = SZ_16G / PUD_SIZE;
> + else
> + nb = 1;
On 4K, hugepages are either 16M or 16G. How can we end up in a situation
whwere the is pte is huge, but is is neither MMU_PAGE_16G nor MMU_PAGE_16M?
> diff --git a/arch/powerpc/mm/book3s64/hugetlbpage.c b/arch/powerpc/mm/book3s64/hugetlbpage.c
> index 5a2e512e96db..83c3361b358b 100644
> --- a/arch/powerpc/mm/book3s64/hugetlbpage.c
> +++ b/arch/powerpc/mm/book3s64/hugetlbpage.c
> @@ -53,6 +53,16 @@ int __hash_page_huge(unsigned long ea, unsigned long access, unsigned long vsid,
> /* If PTE permissions don't match, take page fault */
> if (unlikely(!check_pte_access(access, old_pte)))
> return 1;
> + /*
> + * If hash-4k, hugepages use seeral contiguous PxD entries
'several'
> + * so bail out and let mm make the page young or dirty
> + */
> + if (IS_ENABLED(CONFIG_PPC_4K_PAGES)) {
> + if (!(old_pte & _PAGE_ACCESSED))
> + return 1;
> + if ((access & _PAGE_WRITE) && !(old_pte & _PAGE_DIRTY))
> + return 1;
I have 0 clue about this code. What would happen if we do not bail out?
--
Oscar Salvador
SUSE Labs
