Messages in this thread | | | Subject | Re: [PATCH 3/3] powerpc/8xx: Provide ptep_get() with 16k pages | From | Christophe Leroy <> | Date | Thu, 18 Jun 2020 16:21:16 +0200 |
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Le 18/06/2020 à 02:58, Michael Ellerman a écrit : > Peter Zijlstra <peterz@infradead.org> writes: >> On Thu, Jun 18, 2020 at 12:21:22AM +1000, Michael Ellerman wrote: >>> Peter Zijlstra <peterz@infradead.org> writes: >>>> On Mon, Jun 15, 2020 at 12:57:59PM +0000, Christophe Leroy wrote: >> >>>>> +#if defined(CONFIG_PPC_8xx) && defined(CONFIG_PPC_16K_PAGES) >>>>> +#define __HAVE_ARCH_PTEP_GET >>>>> +static inline pte_t ptep_get(pte_t *ptep) >>>>> +{ >>>>> + pte_t pte = {READ_ONCE(ptep->pte), 0, 0, 0}; >>>>> + >>>>> + return pte; >>>>> +} >>>>> +#endif >>>> >>>> Would it make sense to have a comment with this magic? The casual reader >>>> might wonder WTH just happened when he stumbles on this :-) >>> >>> I tried writing a helpful comment but it's too late for my brain to form >>> sensible sentences. >>> >>> Christophe can you send a follow-up with a comment explaining it? In >>> particular the zero entries stand out, it's kind of subtle that those >>> entries are only populated with the right value when we write to the >>> page table. >> >> static inline pte_t ptep_get(pte_t *ptep) >> { >> unsigned long val = READ_ONCE(ptep->pte); >> /* 16K pages have 4 identical value 4K entries */ >> pte_t pte = {val, val, val, val); >> return pte; >> } >> >> Maybe something like that? > > I think val wants to be pte_basic_t, but otherwise yeah I like that much > better. >
I sent a patch for that.
I'll also send one to fix mm/debug_vm_pgtable.c which also uses READ_ONCE() to access page table entries.
Christophe
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