Le 23/01/2024 à 12:08, Ryan Roberts a écrit : > On 23/01/2024 10:48, David Hildenbrand wrote: >> On 23.01.24 11:34, Ryan Roberts wrote: >>> On 22/01/2024 19:41, David Hildenbrand wrote: >>>> We want to make use of pte_next_pfn() outside of set_ptes(). Let's >>>> simpliy define PFN_PTE_SHIFT, required by pte_next_pfn(). >>>> >>>> Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> >>>> --- >>>> arch/arm/include/asm/pgtable.h | 2 ++ >>>> arch/arm64/include/asm/pgtable.h | 2 ++ >>>> 2 files changed, 4 insertions(+) >>>> >>>> diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h >>>> index d657b84b6bf70..be91e376df79e 100644 >>>> --- a/arch/arm/include/asm/pgtable.h >>>> +++ b/arch/arm/include/asm/pgtable.h >>>> @@ -209,6 +209,8 @@ static inline void __sync_icache_dcache(pte_t pteval) >>>> extern void __sync_icache_dcache(pte_t pteval); >>>> #endif >>>> +#define PFN_PTE_SHIFT PAGE_SHIFT >>>> + >>>> void set_ptes(struct mm_struct *mm, unsigned long addr, >>>> pte_t *ptep, pte_t pteval, unsigned int nr); >>>> #define set_ptes set_ptes >>>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h >>>> index 79ce70fbb751c..d4b3bd96e3304 100644 >>>> --- a/arch/arm64/include/asm/pgtable.h >>>> +++ b/arch/arm64/include/asm/pgtable.h >>>> @@ -341,6 +341,8 @@ static inline void __sync_cache_and_tags(pte_t pte, >>>> unsigned int nr_pages) >>>> mte_sync_tags(pte, nr_pages); >>>> } >>>> +#define PFN_PTE_SHIFT PAGE_SHIFT >>> >>> I think this is buggy. And so is the arm64 implementation of set_ptes(). It >>> works fine for 48-bit output address, but for 52-bit OAs, the high bits are not >>> kept contigously, so if you happen to be setting a mapping for which the >>> physical memory block straddles bit 48, this won't work. >> >> Right, as soon as the PTE bits are not contiguous, this stops working, just like >> set_ptes() would, which I used as orientation. >> >>> >>> Today, only the 64K base page config can support 52 bits, and for this, >>> OA[51:48] are stored in PTE[15:12]. But 52 bits for 4K and 16K base pages is >>> coming (hopefully v6.9) and in this case OA[51:50] are stored in PTE[9:8]. >>> Fortunately we already have helpers in arm64 to abstract this. >>> >>> So I think arm64 will want to define its own pte_next_pfn(): >>> >>> #define pte_next_pfn pte_next_pfn >>> static inline pte_t pte_next_pfn(pte_t pte) >>> { >>> return pfn_pte(pte_pfn(pte) + 1, pte_pgprot(pte)); >>> } >>> >>> I'll do a separate patch to fix the already broken arm64 set_ptes() >>> implementation. >> >> Make sense. >> >>> >>> I'm not sure if this type of problem might also apply to other arches? >> >> I saw similar handling in the PPC implementation of set_ptes, but was not able >> to convince me that it is actually required there. >> >> pte_pfn on ppc does: >> >> static inline unsigned long pte_pfn(pte_t pte) >> { >> return (pte_val(pte) & PTE_RPN_MASK) >> PTE_RPN_SHIFT; >> } >> >> But that means that the PFNs *are* contiguous. > > all the ppc pfn_pte() implementations also only shift the pfn, so I think ppc is > safe to just define PFN_PTE_SHIFT. Although 2 of the 3 implementations shift by > PTE_RPN_SHIFT and the other shifts by PAGE_SIZE, so you might want to define > PFN_PTE_SHIFT separately for all 3 configs? We have PTE_RPN_SHIFT defined for all 4 implementations, for some of them you are right it is defined as PAGE_SHIFT, but I see no reason to define PFN_PTE_SHIFT separately. > >> If high bits are used for >> something else, then we might produce a garbage PTE on overflow, but that >> shouldn't really matter I concluded for folio_pte_batch() purposes, we'd not >> detect "belongs to this folio batch" either way. > > Exactly. > >> >> Maybe it's likely cleaner to also have a custom pte_next_pfn() on ppc, I just >> hope that we don't lose any other arbitrary PTE bits by doing the pte_pgprot(). > > I don't see the need for ppc to implement pte_next_pfn(). Agreed. > > pte_pgprot() is not a "proper" arch interface (its only required by the core-mm > if the arch implements a certain Kconfig IIRC). For arm64, all bits that are not > pfn are pgprot, so there are no bits lost. > >> >> >> I guess pte_pfn() implementations should tell us if anything special needs to >> happen. >> >