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? > 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(). 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. >