Christophe Leroy <christophe.leroy@xxxxxx> writes:
> Hi,
>
> I'm having a hard time figuring out the best way to handle the following
> situation:
>
> On the powerpc8xx, handling 16k size pages requires to have page tables
> with 4 identical entries.
I assume that hugetlb page size? If so isn't that similar to FSL hugetlb
page table layout?
>
> Initially I was thinking about handling this by simply modifying
> pte_index() which changing pte_t type in order to have one entry every
> 16 bytes, then replicate the PTE value at *ptep, *ptep+1,*ptep+2 and
> *ptep+3 both in set_pte_at() and pte_update().
>
> However, this doesn't work because many many places in the mm core part
> of the kernel use loops on ptep with single ptep++ increment.
>
> Therefore did it with the following hack:
>
> /* PTE level */
> +#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES)
> +typedef struct { pte_basic_t pte, pte1, pte2, pte3; } pte_t;
> +#else
> typedef struct { pte_basic_t pte; } pte_t;
> +#endif
>
> @@ -181,7 +192,13 @@ static inline unsigned long pte_update(pte_t *p,
> : "cc" );
> #else /* PTE_ATOMIC_UPDATES */
> unsigned long old = pte_val(*p);
> - *p = __pte((old & ~clr) | set);
> + unsigned long new = (old & ~clr) | set;
> +
> +#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES)
> + p->pte = p->pte1 = p->pte2 = p->pte3 = new;
> +#else
> + *p = __pte(new);
> +#endif
> #endif /* !PTE_ATOMIC_UPDATES */
>
> #ifdef CONFIG_44x
>
>
> @@ -161,7 +161,11 @@ static inline void __set_pte_at(struct mm_struct
> *mm, unsigned long addr,
> /* Anything else just stores the PTE normally. That covers all
> 64-bit
> * cases, and 32-bit non-hash with 32-bit PTEs.
> */
> +#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES)
> + ptep->pte = ptep->pte1 = ptep->pte2 = ptep->pte3 = pte_val(pte);
> +#else
> *ptep = pte;
> +#endif
>
>
>
> But I'm not too happy with it as it means pte_t is not a single type
> anymore so passing it from one function to the other is quite heavy.
>
>
> Would someone have an idea of an elegent way to handle that ?
>
> Thanks
> Christophe
Why would pte_update bother about updating all the 4 entries?. Can you
help me understand the issue?
-aneesh
