On Sun, May 26, 2024 at 11:22:20AM +0200, Christophe Leroy wrote: > This is the continuation of the RFC v1 series "Reimplement huge pages > without hugepd on powerpc 8xx". It now get rid of hugepd completely > after handling also e500 and book3s/64 > > Also see https://github.com/linuxppc/issues/issues/483 > > Unlike most architectures, powerpc 8xx HW requires a two-level > pagetable topology for all page sizes. So a leaf PMD-contig approach > is not feasible as such. > > Possible sizes on 8xx are 4k, 16k, 512k and 8M. > > First level (PGD/PMD) covers 4M per entry. For 8M pages, two PMD entries > must point to a single entry level-2 page table. Until now that was > done using hugepd. This series changes it to use standard page tables > where the entry is replicated 1024 times on each of the two pagetables > refered by the two associated PMD entries for that 8M page. > > For e500 and book3s/64 there are less constraints because it is not > tied to the HW assisted tablewalk like on 8xx, so it is easier to use > leaf PMDs (and PUDs). > > On e500 the supported page sizes are 4M, 16M, 64M, 256M and 1G. All at > PMD level on e500/32 (mpc85xx) and mix of PMD and PUD for e500/64. We > encode page size with 4 available bits in PTE entries. On e300/32 PGD > entries size is increases to 64 bits in order to allow leaf-PMD entries > because PTE are 64 bits on e500. > > On book3s/64 only the hash-4k mode is concerned. It supports 16M pages > as cont-PMD and 16G pages as cont-PUD. In other modes (radix-4k, radix-6k > and hash-64k) the sizes match with PMD and PUD sizes so that's just leaf > entries. The hash processing make things a bit more complex. To ease > things, __hash_page_huge() is modified to bail out when DIRTY or ACCESSED > bits are missing, leaving it to mm core to fix it. > > Global changes in v3: > - Removed patches 1 and 2 > - Squashed patch 11 into patch 5 > - Replaced patches 12 and 13 with a series from Michael > - Reordered patches a bit to have more general patches up front > > For more details on changes, see in each patch. > > Christophe Leroy (15): > mm: Define __pte_leaf_size() to also take a PMD entry > mm: Provide mm_struct and address to huge_ptep_get() > powerpc/mm: Remove _PAGE_PSIZE > powerpc/mm: Fix __find_linux_pte() on 32 bits with PMD leaf entries > powerpc/mm: Allow hugepages without hugepd > powerpc/8xx: Fix size given to set_huge_pte_at() > powerpc/8xx: Rework support for 8M pages using contiguous PTE entries > powerpc/8xx: Simplify struct mmu_psize_def > powerpc/e500: Remove enc and ind fields from struct mmu_psize_def > powerpc/e500: Switch to 64 bits PGD on 85xx (32 bits) > powerpc/e500: Encode hugepage size in PTE bits > powerpc/e500: Use contiguous PMD instead of hugepd > powerpc/64s: Use contiguous PMD/PUD instead of HUGEPD > powerpc/mm: Remove hugepd leftovers > mm: Remove CONFIG_ARCH_HAS_HUGEPD I glanced over it and it looks much better, not having to fiddle with other arch code and generic declarations is a big plus. I plan to do a proper review tomorrow. Thanks for working on this Christophe! -- Oscar Salvador SUSE Labs
