On Mon, 10 Sep 2018 14:34:37 +0000 Christophe Leroy <christophe.le...@c-s.fr> wrote:
> 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. > > 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 ? I can't think of anything better. Do we pass pte by value to a lot of non inlined functions? Possible to inline the important ones? Other option, try to get an iterator like pte = pte_next(pte) into core code. Thanks, Nick