Messages in this thread | | | Subject | Re: How to handle PTE tables with non contiguous entries ? | From | Christophe LEROY <> | Date | Tue, 11 Sep 2018 07:39:50 +0200 |
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Le 10/09/2018 à 23:06, Nicholas Piggin a écrit : > On Mon, 10 Sep 2018 14:34:37 +0000 > Christophe Leroy <christophe.leroy@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?
Good question, I need to check that.
> > Other option, try to get an iterator like pte = pte_next(pte) into core > code.
Yes I've been thinking about that, but it looks like a huge job to identify all places, as some drivers are also playing with it. I'm not sure it is only to find all 'pte++' and 'ptep++', I fear there might be places with more unexpected names.
Thanks Christophe
> > Thanks, > Nick >
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