| Message ID | 20231115163018.1303287-13-ryan.roberts@arm.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | Transparent Contiguous PTEs for User Mappings | expand |
Ryan Roberts <ryan.roberts@arm.com> writes: [...] > +static void contpte_fold(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, pte_t pte, bool fold) > +{ > + struct vm_area_struct vma = TLB_FLUSH_VMA(mm, 0); > + unsigned long start_addr; > + pte_t *start_ptep; > + int i; > + > + start_ptep = ptep = contpte_align_down(ptep); > + start_addr = addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); > + pte = pfn_pte(ALIGN_DOWN(pte_pfn(pte), CONT_PTES), pte_pgprot(pte)); > + pte = fold ? pte_mkcont(pte) : pte_mknoncont(pte); > + > + for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) { > + pte_t ptent = __ptep_get_and_clear(mm, addr, ptep); > + > + if (pte_dirty(ptent)) > + pte = pte_mkdirty(pte); > + > + if (pte_young(ptent)) > + pte = pte_mkyoung(pte); > + } > + > + __flush_tlb_range(&vma, start_addr, addr, PAGE_SIZE, true, 3); > + > + __set_ptes(mm, start_addr, start_ptep, pte, CONT_PTES); > +} > + > +void __contpte_try_fold(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, pte_t pte) > +{ > + /* > + * We have already checked that the virtual and pysical addresses are > + * correctly aligned for a contpte mapping in contpte_try_fold() so the > + * remaining checks are to ensure that the contpte range is fully > + * covered by a single folio, and ensure that all the ptes are valid > + * with contiguous PFNs and matching prots. We ignore the state of the > + * access and dirty bits for the purpose of deciding if its a contiguous > + * range; the folding process will generate a single contpte entry which > + * has a single access and dirty bit. Those 2 bits are the logical OR of > + * their respective bits in the constituent pte entries. In order to > + * ensure the contpte range is covered by a single folio, we must > + * recover the folio from the pfn, but special mappings don't have a > + * folio backing them. Fortunately contpte_try_fold() already checked > + * that the pte is not special - we never try to fold special mappings. > + * Note we can't use vm_normal_page() for this since we don't have the > + * vma. > + */ > + > + struct page *page = pte_page(pte); > + struct folio *folio = page_folio(page); > + unsigned long folio_saddr = addr - (page - &folio->page) * PAGE_SIZE; > + unsigned long folio_eaddr = folio_saddr + folio_nr_pages(folio) * PAGE_SIZE; > + unsigned long cont_saddr = ALIGN_DOWN(addr, CONT_PTE_SIZE); > + unsigned long cont_eaddr = cont_saddr + CONT_PTE_SIZE; > + unsigned long pfn; > + pgprot_t prot; > + pte_t subpte; > + pte_t *orig_ptep; > + int i; > + > + if (folio_saddr > cont_saddr || folio_eaddr < cont_eaddr) > + return; > + > + pfn = pte_pfn(pte) - ((addr - cont_saddr) >> PAGE_SHIFT); > + prot = pte_pgprot(pte_mkold(pte_mkclean(pte))); > + orig_ptep = ptep; > + ptep = contpte_align_down(ptep); > + > + for (i = 0; i < CONT_PTES; i++, ptep++, pfn++) { > + subpte = __ptep_get(ptep); > + subpte = pte_mkold(pte_mkclean(subpte)); > + > + if (!pte_valid(subpte) || > + pte_pfn(subpte) != pfn || > + pgprot_val(pte_pgprot(subpte)) != pgprot_val(prot)) > + return; > + } > + > + contpte_fold(mm, addr, orig_ptep, pte, true); > +} > +EXPORT_SYMBOL(__contpte_try_fold); > + > +void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, pte_t pte) > +{ > + /* > + * We have already checked that the ptes are contiguous in > + * contpte_try_unfold(), so we can unfold unconditionally here. > + */ > + > + contpte_fold(mm, addr, ptep, pte, false); I'm still working my way through the series but calling a fold during an unfold stood out as it seemed wrong. Obviously further reading revealed the boolean flag that changes the functions meaning but I think it would be better to refactor that. We could easily rename contpte_fold() to eg. set_cont_ptes() and factor the pte calculation loop into a separate helper (eg. calculate_contpte_dirty_young() or some hopefully better name) called further up the stack. That has an added benefit of providing a spot to add the nice comment for young/dirty rules you provided in the patch description ;-) In other words we'd have something like: void __contpte_try_unfold() { pte = calculate_contpte_dirty_young(mm, addr, ptep, pte); pte = pte_mknoncont(pte); set_cont_ptes(mm, addr, ptep, pte); } Which IMHO is more immediately understandable. - Alistair > +} > +EXPORT_SYMBOL(__contpte_try_unfold); > + > +pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte) > +{ > + /* > + * Gather access/dirty bits, which may be populated in any of the ptes > + * of the contig range. We are guarranteed to be holding the PTL, so any > + * contiguous range cannot be unfolded or otherwise modified under our > + * feet. > + */ > + > + pte_t pte; > + int i; > + > + ptep = contpte_align_down(ptep); > + > + for (i = 0; i < CONT_PTES; i++, ptep++) { > + pte = __ptep_get(ptep); > + > + if (pte_dirty(pte)) > + orig_pte = pte_mkdirty(orig_pte); > + > + if (pte_young(pte)) > + orig_pte = pte_mkyoung(orig_pte); > + } > + > + return orig_pte; > +} > +EXPORT_SYMBOL(contpte_ptep_get); > + > +pte_t contpte_ptep_get_lockless(pte_t *orig_ptep) > +{ > + /* > + * Gather access/dirty bits, which may be populated in any of the ptes > + * of the contig range. We may not be holding the PTL, so any contiguous > + * range may be unfolded/modified/refolded under our feet. Therefore we > + * ensure we read a _consistent_ contpte range by checking that all ptes > + * in the range are valid and have CONT_PTE set, that all pfns are > + * contiguous and that all pgprots are the same (ignoring access/dirty). > + * If we find a pte that is not consistent, then we must be racing with > + * an update so start again. If the target pte does not have CONT_PTE > + * set then that is considered consistent on its own because it is not > + * part of a contpte range. > + */ > + > + pte_t orig_pte; > + pgprot_t orig_prot; > + pte_t *ptep; > + unsigned long pfn; > + pte_t pte; > + pgprot_t prot; > + int i; > + > +retry: > + orig_pte = __ptep_get(orig_ptep); > + > + if (!pte_valid_cont(orig_pte)) > + return orig_pte; > + > + orig_prot = pte_pgprot(pte_mkold(pte_mkclean(orig_pte))); > + ptep = contpte_align_down(orig_ptep); > + pfn = pte_pfn(orig_pte) - (orig_ptep - ptep); > + > + for (i = 0; i < CONT_PTES; i++, ptep++, pfn++) { > + pte = __ptep_get(ptep); > + prot = pte_pgprot(pte_mkold(pte_mkclean(pte))); > + > + if (!pte_valid_cont(pte) || > + pte_pfn(pte) != pfn || > + pgprot_val(prot) != pgprot_val(orig_prot)) > + goto retry; > + > + if (pte_dirty(pte)) > + orig_pte = pte_mkdirty(orig_pte); > + > + if (pte_young(pte)) > + orig_pte = pte_mkyoung(orig_pte); > + } > + > + return orig_pte; > +} > +EXPORT_SYMBOL(contpte_ptep_get_lockless); > + > +void contpte_set_ptes(struct mm_struct *mm, unsigned long addr, > + pte_t *ptep, pte_t pte, unsigned int nr) > +{ > + unsigned long next; > + unsigned long end = addr + (nr << PAGE_SHIFT); > + unsigned long pfn = pte_pfn(pte); > + pgprot_t prot = pte_pgprot(pte); > + pte_t orig_pte; > + > + do { > + next = pte_cont_addr_end(addr, end); > + nr = (next - addr) >> PAGE_SHIFT; > + pte = pfn_pte(pfn, prot); > + > + if (((addr | next | (pfn << PAGE_SHIFT)) & ~CONT_PTE_MASK) == 0) > + pte = pte_mkcont(pte); > + else > + pte = pte_mknoncont(pte); > + > + /* > + * If operating on a partial contiguous range then we must first > + * unfold the contiguous range if it was previously folded. > + * Otherwise we could end up with overlapping tlb entries. > + */ > + if (nr != CONT_PTES) > + contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep)); > + > + /* > + * If we are replacing ptes that were contiguous or if the new > + * ptes are contiguous and any of the ptes being replaced are > + * valid, we need to clear and flush the range to prevent > + * overlapping tlb entries. > + */ > + orig_pte = __ptep_get(ptep); > + if (pte_valid_cont(orig_pte) || > + (pte_cont(pte) && ptep_any_valid(ptep, nr))) > + ptep_clear_flush_range(mm, addr, ptep, nr); > + > + __set_ptes(mm, addr, ptep, pte, nr); > + > + addr = next; > + ptep += nr; > + pfn += nr; > + > + } while (addr != end); > +} > +EXPORT_SYMBOL(contpte_set_ptes); > + > +int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma, > + unsigned long addr, pte_t *ptep) > +{ > + /* > + * ptep_clear_flush_young() technically requires us to clear the access > + * flag for a _single_ pte. However, the core-mm code actually tracks > + * access/dirty per folio, not per page. And since we only create a > + * contig range when the range is covered by a single folio, we can get > + * away with clearing young for the whole contig range here, so we avoid > + * having to unfold. > + */ > + > + int i; > + int young = 0; > + > + ptep = contpte_align_down(ptep); > + addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); > + > + for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) > + young |= __ptep_test_and_clear_young(vma, addr, ptep); > + > + return young; > +} > +EXPORT_SYMBOL(contpte_ptep_test_and_clear_young); > + > +int contpte_ptep_clear_flush_young(struct vm_area_struct *vma, > + unsigned long addr, pte_t *ptep) > +{ > + int young; > + > + young = contpte_ptep_test_and_clear_young(vma, addr, ptep); > + > + if (young) { > + /* > + * See comment in __ptep_clear_flush_young(); same rationale for > + * eliding the trailing DSB applies here. > + */ > + addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); > + __flush_tlb_range_nosync(vma, addr, addr + CONT_PTE_SIZE, > + PAGE_SIZE, true, 3); > + } > + > + return young; > +} > +EXPORT_SYMBOL(contpte_ptep_clear_flush_young); > + > +int contpte_ptep_set_access_flags(struct vm_area_struct *vma, > + unsigned long addr, pte_t *ptep, > + pte_t entry, int dirty) > +{ > + pte_t orig_pte; > + int i; > + unsigned long start_addr; > + > + /* > + * Gather the access/dirty bits for the contiguous range. If nothing has > + * changed, its a noop. > + */ > + orig_pte = ptep_get(ptep); > + if (pte_val(orig_pte) == pte_val(entry)) > + return 0; > + > + /* > + * We can fix up access/dirty bits without having to unfold/fold the > + * contig range. But if the write bit is changing, we need to go through > + * the full unfold/fold cycle. > + */ > + if (pte_write(orig_pte) == pte_write(entry)) { > + /* > + * For HW access management, we technically only need to update > + * the flag on a single pte in the range. But for SW access > + * management, we need to update all the ptes to prevent extra > + * faults. Avoid per-page tlb flush in __ptep_set_access_flags() > + * and instead flush the whole range at the end. > + */ > + ptep = contpte_align_down(ptep); > + start_addr = addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); > + > + for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) > + __ptep_set_access_flags(vma, addr, ptep, entry, 0); > + > + if (dirty) > + __flush_tlb_range(vma, start_addr, addr, > + PAGE_SIZE, true, 3); > + } else { > + __contpte_try_unfold(vma->vm_mm, addr, ptep, orig_pte); > + __ptep_set_access_flags(vma, addr, ptep, entry, dirty); > + contpte_try_fold(vma->vm_mm, addr, ptep, entry); > + } > + > + return 1; > +} > +EXPORT_SYMBOL(contpte_ptep_set_access_flags);
On 21/11/2023 11:22, Alistair Popple wrote: > > Ryan Roberts <ryan.roberts@arm.com> writes: > > [...] > >> +static void contpte_fold(struct mm_struct *mm, unsigned long addr, >> + pte_t *ptep, pte_t pte, bool fold) >> +{ >> + struct vm_area_struct vma = TLB_FLUSH_VMA(mm, 0); >> + unsigned long start_addr; >> + pte_t *start_ptep; >> + int i; >> + >> + start_ptep = ptep = contpte_align_down(ptep); >> + start_addr = addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); >> + pte = pfn_pte(ALIGN_DOWN(pte_pfn(pte), CONT_PTES), pte_pgprot(pte)); >> + pte = fold ? pte_mkcont(pte) : pte_mknoncont(pte); >> + >> + for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) { >> + pte_t ptent = __ptep_get_and_clear(mm, addr, ptep); >> + >> + if (pte_dirty(ptent)) >> + pte = pte_mkdirty(pte); >> + >> + if (pte_young(ptent)) >> + pte = pte_mkyoung(pte); >> + } >> + >> + __flush_tlb_range(&vma, start_addr, addr, PAGE_SIZE, true, 3); >> + >> + __set_ptes(mm, start_addr, start_ptep, pte, CONT_PTES); >> +} >> + >> +void __contpte_try_fold(struct mm_struct *mm, unsigned long addr, >> + pte_t *ptep, pte_t pte) >> +{ >> + /* >> + * We have already checked that the virtual and pysical addresses are >> + * correctly aligned for a contpte mapping in contpte_try_fold() so the >> + * remaining checks are to ensure that the contpte range is fully >> + * covered by a single folio, and ensure that all the ptes are valid >> + * with contiguous PFNs and matching prots. We ignore the state of the >> + * access and dirty bits for the purpose of deciding if its a contiguous >> + * range; the folding process will generate a single contpte entry which >> + * has a single access and dirty bit. Those 2 bits are the logical OR of >> + * their respective bits in the constituent pte entries. In order to >> + * ensure the contpte range is covered by a single folio, we must >> + * recover the folio from the pfn, but special mappings don't have a >> + * folio backing them. Fortunately contpte_try_fold() already checked >> + * that the pte is not special - we never try to fold special mappings. >> + * Note we can't use vm_normal_page() for this since we don't have the >> + * vma. >> + */ >> + >> + struct page *page = pte_page(pte); >> + struct folio *folio = page_folio(page); >> + unsigned long folio_saddr = addr - (page - &folio->page) * PAGE_SIZE; >> + unsigned long folio_eaddr = folio_saddr + folio_nr_pages(folio) * PAGE_SIZE; >> + unsigned long cont_saddr = ALIGN_DOWN(addr, CONT_PTE_SIZE); >> + unsigned long cont_eaddr = cont_saddr + CONT_PTE_SIZE; >> + unsigned long pfn; >> + pgprot_t prot; >> + pte_t subpte; >> + pte_t *orig_ptep; >> + int i; >> + >> + if (folio_saddr > cont_saddr || folio_eaddr < cont_eaddr) >> + return; >> + >> + pfn = pte_pfn(pte) - ((addr - cont_saddr) >> PAGE_SHIFT); >> + prot = pte_pgprot(pte_mkold(pte_mkclean(pte))); >> + orig_ptep = ptep; >> + ptep = contpte_align_down(ptep); >> + >> + for (i = 0; i < CONT_PTES; i++, ptep++, pfn++) { >> + subpte = __ptep_get(ptep); >> + subpte = pte_mkold(pte_mkclean(subpte)); >> + >> + if (!pte_valid(subpte) || >> + pte_pfn(subpte) != pfn || >> + pgprot_val(pte_pgprot(subpte)) != pgprot_val(prot)) >> + return; >> + } >> + >> + contpte_fold(mm, addr, orig_ptep, pte, true); >> +} >> +EXPORT_SYMBOL(__contpte_try_fold); >> + >> +void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr, >> + pte_t *ptep, pte_t pte) >> +{ >> + /* >> + * We have already checked that the ptes are contiguous in >> + * contpte_try_unfold(), so we can unfold unconditionally here. >> + */ >> + >> + contpte_fold(mm, addr, ptep, pte, false); > > I'm still working my way through the series but Thanks for taking the time to review! > calling a fold during an > unfold stood out as it seemed wrong. Obviously further reading revealed > the boolean flag that changes the functions meaning but I think it would > be better to refactor that. Yes that sounds reasonable. > > We could easily rename contpte_fold() to eg. set_cont_ptes() and factor > the pte calculation loop into a separate helper > (eg. calculate_contpte_dirty_young() or some hopefully better name) > called further up the stack. That has an added benefit of providing a > spot to add the nice comment for young/dirty rules you provided in the > patch description ;-) > > In other words we'd have something like: > > void __contpte_try_unfold() { > pte = calculate_contpte_dirty_young(mm, addr, ptep, pte); > pte = pte_mknoncont(pte); > set_cont_ptes(mm, addr, ptep, pte); > } My concern with this approach is that calculate_contpte_dirty_young() has side effects; it has to clear each PTE as it loops through it prevent a race between our reading access/dirty and another thread causing access/dirty to be set. So its not just a "calculation", its the teardown portion of the process too. I guess its a taste thing, so happy for it to be argued the other way, but I would prefer to keep it all together in one function. How about renaming contpte_fold() to contpte_convert() or contpte_repaint() (other suggestions welcome), and extracting the pte_mkcont()/pte_mknoncont() part (so we can remove the bool param): void __contpte_try_unfold() { pte = pte_mknoncont(pte); contpte_convert(mm, addr, ptep, pte); } Thanks, Ryan > > Which IMHO is more immediately understandable. > > - Alistair >
Ryan Roberts <ryan.roberts@arm.com> writes: > On 21/11/2023 11:22, Alistair Popple wrote: >> >> Ryan Roberts <ryan.roberts@arm.com> writes: >> >> [...] >> >>> +static void contpte_fold(struct mm_struct *mm, unsigned long addr, >>> + pte_t *ptep, pte_t pte, bool fold) >>> +{ >>> + struct vm_area_struct vma = TLB_FLUSH_VMA(mm, 0); >>> + unsigned long start_addr; >>> + pte_t *start_ptep; >>> + int i; >>> + >>> + start_ptep = ptep = contpte_align_down(ptep); >>> + start_addr = addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); >>> + pte = pfn_pte(ALIGN_DOWN(pte_pfn(pte), CONT_PTES), pte_pgprot(pte)); >>> + pte = fold ? pte_mkcont(pte) : pte_mknoncont(pte); >>> + >>> + for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) { >>> + pte_t ptent = __ptep_get_and_clear(mm, addr, ptep); >>> + >>> + if (pte_dirty(ptent)) >>> + pte = pte_mkdirty(pte); >>> + >>> + if (pte_young(ptent)) >>> + pte = pte_mkyoung(pte); >>> + } >>> + >>> + __flush_tlb_range(&vma, start_addr, addr, PAGE_SIZE, true, 3); >>> + >>> + __set_ptes(mm, start_addr, start_ptep, pte, CONT_PTES); >>> +} >>> + >>> +void __contpte_try_fold(struct mm_struct *mm, unsigned long addr, >>> + pte_t *ptep, pte_t pte) >>> +{ >>> + /* >>> + * We have already checked that the virtual and pysical addresses are >>> + * correctly aligned for a contpte mapping in contpte_try_fold() so the >>> + * remaining checks are to ensure that the contpte range is fully >>> + * covered by a single folio, and ensure that all the ptes are valid >>> + * with contiguous PFNs and matching prots. We ignore the state of the >>> + * access and dirty bits for the purpose of deciding if its a contiguous >>> + * range; the folding process will generate a single contpte entry which >>> + * has a single access and dirty bit. Those 2 bits are the logical OR of >>> + * their respective bits in the constituent pte entries. In order to >>> + * ensure the contpte range is covered by a single folio, we must >>> + * recover the folio from the pfn, but special mappings don't have a >>> + * folio backing them. Fortunately contpte_try_fold() already checked >>> + * that the pte is not special - we never try to fold special mappings. >>> + * Note we can't use vm_normal_page() for this since we don't have the >>> + * vma. >>> + */ >>> + >>> + struct page *page = pte_page(pte); >>> + struct folio *folio = page_folio(page); >>> + unsigned long folio_saddr = addr - (page - &folio->page) * PAGE_SIZE; >>> + unsigned long folio_eaddr = folio_saddr + folio_nr_pages(folio) * PAGE_SIZE; >>> + unsigned long cont_saddr = ALIGN_DOWN(addr, CONT_PTE_SIZE); >>> + unsigned long cont_eaddr = cont_saddr + CONT_PTE_SIZE; >>> + unsigned long pfn; >>> + pgprot_t prot; >>> + pte_t subpte; >>> + pte_t *orig_ptep; >>> + int i; >>> + >>> + if (folio_saddr > cont_saddr || folio_eaddr < cont_eaddr) >>> + return; >>> + >>> + pfn = pte_pfn(pte) - ((addr - cont_saddr) >> PAGE_SHIFT); >>> + prot = pte_pgprot(pte_mkold(pte_mkclean(pte))); >>> + orig_ptep = ptep; >>> + ptep = contpte_align_down(ptep); >>> + >>> + for (i = 0; i < CONT_PTES; i++, ptep++, pfn++) { >>> + subpte = __ptep_get(ptep); >>> + subpte = pte_mkold(pte_mkclean(subpte)); >>> + >>> + if (!pte_valid(subpte) || >>> + pte_pfn(subpte) != pfn || >>> + pgprot_val(pte_pgprot(subpte)) != pgprot_val(prot)) >>> + return; >>> + } >>> + >>> + contpte_fold(mm, addr, orig_ptep, pte, true); >>> +} >>> +EXPORT_SYMBOL(__contpte_try_fold); >>> + >>> +void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr, >>> + pte_t *ptep, pte_t pte) >>> +{ >>> + /* >>> + * We have already checked that the ptes are contiguous in >>> + * contpte_try_unfold(), so we can unfold unconditionally here. >>> + */ >>> + >>> + contpte_fold(mm, addr, ptep, pte, false); >> >> I'm still working my way through the series but > > Thanks for taking the time to review! > >> calling a fold during an >> unfold stood out as it seemed wrong. Obviously further reading revealed >> the boolean flag that changes the functions meaning but I think it would >> be better to refactor that. > > Yes that sounds reasonable. > >> >> We could easily rename contpte_fold() to eg. set_cont_ptes() and factor >> the pte calculation loop into a separate helper >> (eg. calculate_contpte_dirty_young() or some hopefully better name) >> called further up the stack. That has an added benefit of providing a >> spot to add the nice comment for young/dirty rules you provided in the >> patch description ;-) >> >> In other words we'd have something like: >> >> void __contpte_try_unfold() { >> pte = calculate_contpte_dirty_young(mm, addr, ptep, pte); >> pte = pte_mknoncont(pte); >> set_cont_ptes(mm, addr, ptep, pte); >> } > > My concern with this approach is that calculate_contpte_dirty_young() has side > effects; it has to clear each PTE as it loops through it prevent a race between > our reading access/dirty and another thread causing access/dirty to be set. So > its not just a "calculation", its the teardown portion of the process too. I > guess its a taste thing, so happy for it to be argued the other way, but I would > prefer to keep it all together in one function. > > How about renaming contpte_fold() to contpte_convert() or contpte_repaint() > (other suggestions welcome), and extracting the pte_mkcont()/pte_mknoncont() > part (so we can remove the bool param): > > void __contpte_try_unfold() { > pte = pte_mknoncont(pte); > contpte_convert(mm, addr, ptep, pte); > } Thanks. That works for me, although sadly I don't have any better ideas for names atm. - Alistair > Thanks, > Ryan > >> >> Which IMHO is more immediately understandable. >> >> - Alistair >>
On 22/11/2023 06:01, Alistair Popple wrote: > > Ryan Roberts <ryan.roberts@arm.com> writes: > >> On 21/11/2023 11:22, Alistair Popple wrote: >>> >>> Ryan Roberts <ryan.roberts@arm.com> writes: >>> >>> [...] >>> >>>> +static void contpte_fold(struct mm_struct *mm, unsigned long addr, >>>> + pte_t *ptep, pte_t pte, bool fold) >>>> +{ >>>> + struct vm_area_struct vma = TLB_FLUSH_VMA(mm, 0); >>>> + unsigned long start_addr; >>>> + pte_t *start_ptep; >>>> + int i; >>>> + >>>> + start_ptep = ptep = contpte_align_down(ptep); >>>> + start_addr = addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); >>>> + pte = pfn_pte(ALIGN_DOWN(pte_pfn(pte), CONT_PTES), pte_pgprot(pte)); >>>> + pte = fold ? pte_mkcont(pte) : pte_mknoncont(pte); >>>> + >>>> + for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) { >>>> + pte_t ptent = __ptep_get_and_clear(mm, addr, ptep); >>>> + >>>> + if (pte_dirty(ptent)) >>>> + pte = pte_mkdirty(pte); >>>> + >>>> + if (pte_young(ptent)) >>>> + pte = pte_mkyoung(pte); >>>> + } >>>> + >>>> + __flush_tlb_range(&vma, start_addr, addr, PAGE_SIZE, true, 3); >>>> + >>>> + __set_ptes(mm, start_addr, start_ptep, pte, CONT_PTES); >>>> +} >>>> + >>>> +void __contpte_try_fold(struct mm_struct *mm, unsigned long addr, >>>> + pte_t *ptep, pte_t pte) >>>> +{ >>>> + /* >>>> + * We have already checked that the virtual and pysical addresses are >>>> + * correctly aligned for a contpte mapping in contpte_try_fold() so the >>>> + * remaining checks are to ensure that the contpte range is fully >>>> + * covered by a single folio, and ensure that all the ptes are valid >>>> + * with contiguous PFNs and matching prots. We ignore the state of the >>>> + * access and dirty bits for the purpose of deciding if its a contiguous >>>> + * range; the folding process will generate a single contpte entry which >>>> + * has a single access and dirty bit. Those 2 bits are the logical OR of >>>> + * their respective bits in the constituent pte entries. In order to >>>> + * ensure the contpte range is covered by a single folio, we must >>>> + * recover the folio from the pfn, but special mappings don't have a >>>> + * folio backing them. Fortunately contpte_try_fold() already checked >>>> + * that the pte is not special - we never try to fold special mappings. >>>> + * Note we can't use vm_normal_page() for this since we don't have the >>>> + * vma. >>>> + */ >>>> + >>>> + struct page *page = pte_page(pte); >>>> + struct folio *folio = page_folio(page); >>>> + unsigned long folio_saddr = addr - (page - &folio->page) * PAGE_SIZE; >>>> + unsigned long folio_eaddr = folio_saddr + folio_nr_pages(folio) * PAGE_SIZE; >>>> + unsigned long cont_saddr = ALIGN_DOWN(addr, CONT_PTE_SIZE); >>>> + unsigned long cont_eaddr = cont_saddr + CONT_PTE_SIZE; >>>> + unsigned long pfn; >>>> + pgprot_t prot; >>>> + pte_t subpte; >>>> + pte_t *orig_ptep; >>>> + int i; >>>> + >>>> + if (folio_saddr > cont_saddr || folio_eaddr < cont_eaddr) >>>> + return; >>>> + >>>> + pfn = pte_pfn(pte) - ((addr - cont_saddr) >> PAGE_SHIFT); >>>> + prot = pte_pgprot(pte_mkold(pte_mkclean(pte))); >>>> + orig_ptep = ptep; >>>> + ptep = contpte_align_down(ptep); >>>> + >>>> + for (i = 0; i < CONT_PTES; i++, ptep++, pfn++) { >>>> + subpte = __ptep_get(ptep); >>>> + subpte = pte_mkold(pte_mkclean(subpte)); >>>> + >>>> + if (!pte_valid(subpte) || >>>> + pte_pfn(subpte) != pfn || >>>> + pgprot_val(pte_pgprot(subpte)) != pgprot_val(prot)) >>>> + return; >>>> + } >>>> + >>>> + contpte_fold(mm, addr, orig_ptep, pte, true); >>>> +} >>>> +EXPORT_SYMBOL(__contpte_try_fold); >>>> + >>>> +void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr, >>>> + pte_t *ptep, pte_t pte) >>>> +{ >>>> + /* >>>> + * We have already checked that the ptes are contiguous in >>>> + * contpte_try_unfold(), so we can unfold unconditionally here. >>>> + */ >>>> + >>>> + contpte_fold(mm, addr, ptep, pte, false); >>> >>> I'm still working my way through the series but >> >> Thanks for taking the time to review! >> >>> calling a fold during an >>> unfold stood out as it seemed wrong. Obviously further reading revealed >>> the boolean flag that changes the functions meaning but I think it would >>> be better to refactor that. >> >> Yes that sounds reasonable. >> >>> >>> We could easily rename contpte_fold() to eg. set_cont_ptes() and factor >>> the pte calculation loop into a separate helper >>> (eg. calculate_contpte_dirty_young() or some hopefully better name) >>> called further up the stack. That has an added benefit of providing a >>> spot to add the nice comment for young/dirty rules you provided in the >>> patch description ;-) >>> >>> In other words we'd have something like: >>> >>> void __contpte_try_unfold() { >>> pte = calculate_contpte_dirty_young(mm, addr, ptep, pte); >>> pte = pte_mknoncont(pte); >>> set_cont_ptes(mm, addr, ptep, pte); >>> } >> >> My concern with this approach is that calculate_contpte_dirty_young() has side >> effects; it has to clear each PTE as it loops through it prevent a race between >> our reading access/dirty and another thread causing access/dirty to be set. So >> its not just a "calculation", its the teardown portion of the process too. I >> guess its a taste thing, so happy for it to be argued the other way, but I would >> prefer to keep it all together in one function. >> >> How about renaming contpte_fold() to contpte_convert() or contpte_repaint() >> (other suggestions welcome), and extracting the pte_mkcont()/pte_mknoncont() >> part (so we can remove the bool param): >> >> void __contpte_try_unfold() { >> pte = pte_mknoncont(pte); >> contpte_convert(mm, addr, ptep, pte); >> } > > Thanks. That works for me, although sadly I don't have any better ideas > for names atm. Thanks - I'll make this change for v3 and go with contpte_convert(). > > - Alistair > >> Thanks, >> Ryan >> >>> >>> Which IMHO is more immediately understandable. >>> >>> - Alistair >>> >
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 7b071a00425d..de76e484ff3a 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -2209,6 +2209,15 @@ config UNWIND_PATCH_PAC_INTO_SCS select UNWIND_TABLES select DYNAMIC_SCS +config ARM64_CONTPTE + bool "Contiguous PTE mappings for user memory" if EXPERT + depends on TRANSPARENT_HUGEPAGE + default y + help + When enabled, user mappings are configured using the PTE contiguous + bit, for any mappings that meet the size and alignment requirements. + This reduces TLB pressure and improves performance. + endmenu # "Kernel Features" menu "Boot options" @@ -2318,4 +2327,3 @@ endmenu # "CPU Power Management" source "drivers/acpi/Kconfig" source "arch/arm64/kvm/Kconfig" - diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 6930c14f062f..15bc9cf1eef4 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -133,6 +133,10 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys) */ #define pte_valid_not_user(pte) \ ((pte_val(pte) & (PTE_VALID | PTE_USER | PTE_UXN)) == (PTE_VALID | PTE_UXN)) +/* + * Returns true if the pte is valid and has the contiguous bit set. + */ +#define pte_valid_cont(pte) (pte_valid(pte) && pte_cont(pte)) /* * Could the pte be present in the TLB? We must check mm_tlb_flush_pending * so that we don't erroneously return false for pages that have been @@ -1116,6 +1120,202 @@ extern void ptep_modify_prot_commit(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep, pte_t old_pte, pte_t new_pte); +#ifdef CONFIG_ARM64_CONTPTE + +/* + * The contpte APIs are used to transparently manage the contiguous bit in ptes + * where it is possible and makes sense to do so. The PTE_CONT bit is considered + * a private implementation detail of the public ptep API (see below). + */ +extern void __contpte_try_fold(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pte); +extern void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pte); +extern pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte); +extern pte_t contpte_ptep_get_lockless(pte_t *orig_ptep); +extern void contpte_set_ptes(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pte, unsigned int nr); +extern int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep); +extern int contpte_ptep_clear_flush_young(struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep); +extern int contpte_ptep_set_access_flags(struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep, + pte_t entry, int dirty); + +static inline pte_t *contpte_align_down(pte_t *ptep) +{ + return (pte_t *)(ALIGN_DOWN((unsigned long)ptep >> 3, CONT_PTES) << 3); +} + +static inline bool contpte_is_enabled(struct mm_struct *mm) +{ + /* + * Don't attempt to apply the contig bit to kernel mappings, because + * dynamically adding/removing the contig bit can cause page faults. + * These racing faults are ok for user space, since they get serialized + * on the PTL. But kernel mappings can't tolerate faults. + */ + + return mm != &init_mm; +} + +static inline void contpte_try_fold(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pte) +{ + /* + * Only bother trying if both the virtual and physical addresses are + * aligned and correspond to the last entry in a contig range. The core + * code mostly modifies ranges from low to high, so this is the likely + * the last modification in the contig range, so a good time to fold. + * We can't fold special mappings, because there is no associated folio. + */ + + bool valign = ((unsigned long)ptep >> 3) % CONT_PTES == CONT_PTES - 1; + bool palign = pte_pfn(pte) % CONT_PTES == CONT_PTES - 1; + + if (contpte_is_enabled(mm) && valign && palign && + pte_valid(pte) && !pte_cont(pte) && !pte_special(pte)) + __contpte_try_fold(mm, addr, ptep, pte); +} + +static inline void contpte_try_unfold(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pte) +{ + if (contpte_is_enabled(mm) && pte_valid_cont(pte)) + __contpte_try_unfold(mm, addr, ptep, pte); +} + +/* + * The below functions constitute the public API that arm64 presents to the + * core-mm to manipulate PTE entries within the their page tables (or at least + * this is the subset of the API that arm64 needs to implement). These public + * versions will automatically and transparently apply the contiguous bit where + * it makes sense to do so. Therefore any users that are contig-aware (e.g. + * hugetlb, kernel mapper) should NOT use these APIs, but instead use the + * private versions, which are prefixed with double underscore. All of these + * APIs except for ptep_get_lockless() are expected to be called with the PTL + * held. + */ + +#define ptep_get ptep_get +static inline pte_t ptep_get(pte_t *ptep) +{ + pte_t pte = __ptep_get(ptep); + + if (!pte_valid_cont(pte)) + return pte; + + return contpte_ptep_get(ptep, pte); +} + +#define ptep_get_lockless ptep_get_lockless +static inline pte_t ptep_get_lockless(pte_t *ptep) +{ + pte_t pte = __ptep_get(ptep); + + if (!pte_valid_cont(pte)) + return pte; + + return contpte_ptep_get_lockless(ptep); +} + +static inline void set_pte(pte_t *ptep, pte_t pte) +{ + /* + * We don't have the mm or vaddr so cannot unfold or fold contig entries + * (since it requires tlb maintenance). set_pte() is not used in core + * code, so this should never even be called. Regardless do our best to + * service any call and emit a warning if there is any attempt to set a + * pte on top of an existing contig range. + */ + pte_t orig_pte = __ptep_get(ptep); + + WARN_ON_ONCE(pte_valid_cont(orig_pte)); + __set_pte(ptep, pte_mknoncont(pte)); +} + +#define set_ptes set_ptes +static inline void set_ptes(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pte, unsigned int nr) +{ + pte = pte_mknoncont(pte); + + if (!contpte_is_enabled(mm)) + __set_ptes(mm, addr, ptep, pte, nr); + else if (nr == 1) { + contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep)); + __set_ptes(mm, addr, ptep, pte, nr); + contpte_try_fold(mm, addr, ptep, pte); + } else + contpte_set_ptes(mm, addr, ptep, pte, nr); +} + +static inline void pte_clear(struct mm_struct *mm, + unsigned long addr, pte_t *ptep) +{ + contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep)); + __pte_clear(mm, addr, ptep); +} + +#define __HAVE_ARCH_PTEP_GET_AND_CLEAR +static inline pte_t ptep_get_and_clear(struct mm_struct *mm, + unsigned long addr, pte_t *ptep) +{ + contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep)); + return __ptep_get_and_clear(mm, addr, ptep); +} + +#define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG +static inline int ptep_test_and_clear_young(struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep) +{ + pte_t orig_pte = __ptep_get(ptep); + + if (!pte_valid_cont(orig_pte)) + return __ptep_test_and_clear_young(vma, addr, ptep); + + return contpte_ptep_test_and_clear_young(vma, addr, ptep); +} + +#define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH +static inline int ptep_clear_flush_young(struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep) +{ + pte_t orig_pte = __ptep_get(ptep); + + if (!pte_valid_cont(orig_pte)) + return __ptep_clear_flush_young(vma, addr, ptep); + + return contpte_ptep_clear_flush_young(vma, addr, ptep); +} + +#define __HAVE_ARCH_PTEP_SET_WRPROTECT +static inline void ptep_set_wrprotect(struct mm_struct *mm, + unsigned long addr, pte_t *ptep) +{ + contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep)); + __ptep_set_wrprotect(mm, addr, ptep); + contpte_try_fold(mm, addr, ptep, __ptep_get(ptep)); +} + +#define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS +static inline int ptep_set_access_flags(struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep, + pte_t entry, int dirty) +{ + pte_t orig_pte = __ptep_get(ptep); + + entry = pte_mknoncont(entry); + + if (!pte_valid_cont(orig_pte)) + return __ptep_set_access_flags(vma, addr, ptep, entry, dirty); + + return contpte_ptep_set_access_flags(vma, addr, ptep, entry, dirty); +} + +#else /* CONFIG_ARM64_CONTPTE */ + #define ptep_get __ptep_get #define set_pte __set_pte #define set_ptes __set_ptes @@ -1131,6 +1331,8 @@ extern void ptep_modify_prot_commit(struct vm_area_struct *vma, #define __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS #define ptep_set_access_flags __ptep_set_access_flags +#endif /* CONFIG_ARM64_CONTPTE */ + #endif /* !__ASSEMBLY__ */ #endif /* __ASM_PGTABLE_H */ diff --git a/arch/arm64/mm/Makefile b/arch/arm64/mm/Makefile index dbd1bc95967d..60454256945b 100644 --- a/arch/arm64/mm/Makefile +++ b/arch/arm64/mm/Makefile @@ -3,6 +3,7 @@ obj-y := dma-mapping.o extable.o fault.o init.o \ cache.o copypage.o flush.o \ ioremap.o mmap.o pgd.o mmu.o \ context.o proc.o pageattr.o fixmap.o +obj-$(CONFIG_ARM64_CONTPTE) += contpte.o obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o obj-$(CONFIG_PTDUMP_CORE) += ptdump.o obj-$(CONFIG_PTDUMP_DEBUGFS) += ptdump_debugfs.o diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c new file mode 100644 index 000000000000..667bcf7c3260 --- /dev/null +++ b/arch/arm64/mm/contpte.c @@ -0,0 +1,351 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (C) 2023 ARM Ltd. + */ + +#include <linux/mm.h> +#include <linux/export.h> +#include <asm/tlbflush.h> + +static void ptep_clear_flush_range(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, int nr) +{ + struct vm_area_struct vma = TLB_FLUSH_VMA(mm, 0); + unsigned long start_addr = addr; + int i; + + for (i = 0; i < nr; i++, ptep++, addr += PAGE_SIZE) + __pte_clear(mm, addr, ptep); + + __flush_tlb_range(&vma, start_addr, addr, PAGE_SIZE, true, 3); +} + +static bool ptep_any_valid(pte_t *ptep, int nr) +{ + int i; + + for (i = 0; i < nr; i++, ptep++) { + if (pte_valid(__ptep_get(ptep))) + return true; + } + + return false; +} + +static void contpte_fold(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pte, bool fold) +{ + struct vm_area_struct vma = TLB_FLUSH_VMA(mm, 0); + unsigned long start_addr; + pte_t *start_ptep; + int i; + + start_ptep = ptep = contpte_align_down(ptep); + start_addr = addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); + pte = pfn_pte(ALIGN_DOWN(pte_pfn(pte), CONT_PTES), pte_pgprot(pte)); + pte = fold ? pte_mkcont(pte) : pte_mknoncont(pte); + + for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) { + pte_t ptent = __ptep_get_and_clear(mm, addr, ptep); + + if (pte_dirty(ptent)) + pte = pte_mkdirty(pte); + + if (pte_young(ptent)) + pte = pte_mkyoung(pte); + } + + __flush_tlb_range(&vma, start_addr, addr, PAGE_SIZE, true, 3); + + __set_ptes(mm, start_addr, start_ptep, pte, CONT_PTES); +} + +void __contpte_try_fold(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pte) +{ + /* + * We have already checked that the virtual and pysical addresses are + * correctly aligned for a contpte mapping in contpte_try_fold() so the + * remaining checks are to ensure that the contpte range is fully + * covered by a single folio, and ensure that all the ptes are valid + * with contiguous PFNs and matching prots. We ignore the state of the + * access and dirty bits for the purpose of deciding if its a contiguous + * range; the folding process will generate a single contpte entry which + * has a single access and dirty bit. Those 2 bits are the logical OR of + * their respective bits in the constituent pte entries. In order to + * ensure the contpte range is covered by a single folio, we must + * recover the folio from the pfn, but special mappings don't have a + * folio backing them. Fortunately contpte_try_fold() already checked + * that the pte is not special - we never try to fold special mappings. + * Note we can't use vm_normal_page() for this since we don't have the + * vma. + */ + + struct page *page = pte_page(pte); + struct folio *folio = page_folio(page); + unsigned long folio_saddr = addr - (page - &folio->page) * PAGE_SIZE; + unsigned long folio_eaddr = folio_saddr + folio_nr_pages(folio) * PAGE_SIZE; + unsigned long cont_saddr = ALIGN_DOWN(addr, CONT_PTE_SIZE); + unsigned long cont_eaddr = cont_saddr + CONT_PTE_SIZE; + unsigned long pfn; + pgprot_t prot; + pte_t subpte; + pte_t *orig_ptep; + int i; + + if (folio_saddr > cont_saddr || folio_eaddr < cont_eaddr) + return; + + pfn = pte_pfn(pte) - ((addr - cont_saddr) >> PAGE_SHIFT); + prot = pte_pgprot(pte_mkold(pte_mkclean(pte))); + orig_ptep = ptep; + ptep = contpte_align_down(ptep); + + for (i = 0; i < CONT_PTES; i++, ptep++, pfn++) { + subpte = __ptep_get(ptep); + subpte = pte_mkold(pte_mkclean(subpte)); + + if (!pte_valid(subpte) || + pte_pfn(subpte) != pfn || + pgprot_val(pte_pgprot(subpte)) != pgprot_val(prot)) + return; + } + + contpte_fold(mm, addr, orig_ptep, pte, true); +} +EXPORT_SYMBOL(__contpte_try_fold); + +void __contpte_try_unfold(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pte) +{ + /* + * We have already checked that the ptes are contiguous in + * contpte_try_unfold(), so we can unfold unconditionally here. + */ + + contpte_fold(mm, addr, ptep, pte, false); +} +EXPORT_SYMBOL(__contpte_try_unfold); + +pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte) +{ + /* + * Gather access/dirty bits, which may be populated in any of the ptes + * of the contig range. We are guarranteed to be holding the PTL, so any + * contiguous range cannot be unfolded or otherwise modified under our + * feet. + */ + + pte_t pte; + int i; + + ptep = contpte_align_down(ptep); + + for (i = 0; i < CONT_PTES; i++, ptep++) { + pte = __ptep_get(ptep); + + if (pte_dirty(pte)) + orig_pte = pte_mkdirty(orig_pte); + + if (pte_young(pte)) + orig_pte = pte_mkyoung(orig_pte); + } + + return orig_pte; +} +EXPORT_SYMBOL(contpte_ptep_get); + +pte_t contpte_ptep_get_lockless(pte_t *orig_ptep) +{ + /* + * Gather access/dirty bits, which may be populated in any of the ptes + * of the contig range. We may not be holding the PTL, so any contiguous + * range may be unfolded/modified/refolded under our feet. Therefore we + * ensure we read a _consistent_ contpte range by checking that all ptes + * in the range are valid and have CONT_PTE set, that all pfns are + * contiguous and that all pgprots are the same (ignoring access/dirty). + * If we find a pte that is not consistent, then we must be racing with + * an update so start again. If the target pte does not have CONT_PTE + * set then that is considered consistent on its own because it is not + * part of a contpte range. + */ + + pte_t orig_pte; + pgprot_t orig_prot; + pte_t *ptep; + unsigned long pfn; + pte_t pte; + pgprot_t prot; + int i; + +retry: + orig_pte = __ptep_get(orig_ptep); + + if (!pte_valid_cont(orig_pte)) + return orig_pte; + + orig_prot = pte_pgprot(pte_mkold(pte_mkclean(orig_pte))); + ptep = contpte_align_down(orig_ptep); + pfn = pte_pfn(orig_pte) - (orig_ptep - ptep); + + for (i = 0; i < CONT_PTES; i++, ptep++, pfn++) { + pte = __ptep_get(ptep); + prot = pte_pgprot(pte_mkold(pte_mkclean(pte))); + + if (!pte_valid_cont(pte) || + pte_pfn(pte) != pfn || + pgprot_val(prot) != pgprot_val(orig_prot)) + goto retry; + + if (pte_dirty(pte)) + orig_pte = pte_mkdirty(orig_pte); + + if (pte_young(pte)) + orig_pte = pte_mkyoung(orig_pte); + } + + return orig_pte; +} +EXPORT_SYMBOL(contpte_ptep_get_lockless); + +void contpte_set_ptes(struct mm_struct *mm, unsigned long addr, + pte_t *ptep, pte_t pte, unsigned int nr) +{ + unsigned long next; + unsigned long end = addr + (nr << PAGE_SHIFT); + unsigned long pfn = pte_pfn(pte); + pgprot_t prot = pte_pgprot(pte); + pte_t orig_pte; + + do { + next = pte_cont_addr_end(addr, end); + nr = (next - addr) >> PAGE_SHIFT; + pte = pfn_pte(pfn, prot); + + if (((addr | next | (pfn << PAGE_SHIFT)) & ~CONT_PTE_MASK) == 0) + pte = pte_mkcont(pte); + else + pte = pte_mknoncont(pte); + + /* + * If operating on a partial contiguous range then we must first + * unfold the contiguous range if it was previously folded. + * Otherwise we could end up with overlapping tlb entries. + */ + if (nr != CONT_PTES) + contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep)); + + /* + * If we are replacing ptes that were contiguous or if the new + * ptes are contiguous and any of the ptes being replaced are + * valid, we need to clear and flush the range to prevent + * overlapping tlb entries. + */ + orig_pte = __ptep_get(ptep); + if (pte_valid_cont(orig_pte) || + (pte_cont(pte) && ptep_any_valid(ptep, nr))) + ptep_clear_flush_range(mm, addr, ptep, nr); + + __set_ptes(mm, addr, ptep, pte, nr); + + addr = next; + ptep += nr; + pfn += nr; + + } while (addr != end); +} +EXPORT_SYMBOL(contpte_set_ptes); + +int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep) +{ + /* + * ptep_clear_flush_young() technically requires us to clear the access + * flag for a _single_ pte. However, the core-mm code actually tracks + * access/dirty per folio, not per page. And since we only create a + * contig range when the range is covered by a single folio, we can get + * away with clearing young for the whole contig range here, so we avoid + * having to unfold. + */ + + int i; + int young = 0; + + ptep = contpte_align_down(ptep); + addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); + + for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) + young |= __ptep_test_and_clear_young(vma, addr, ptep); + + return young; +} +EXPORT_SYMBOL(contpte_ptep_test_and_clear_young); + +int contpte_ptep_clear_flush_young(struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep) +{ + int young; + + young = contpte_ptep_test_and_clear_young(vma, addr, ptep); + + if (young) { + /* + * See comment in __ptep_clear_flush_young(); same rationale for + * eliding the trailing DSB applies here. + */ + addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); + __flush_tlb_range_nosync(vma, addr, addr + CONT_PTE_SIZE, + PAGE_SIZE, true, 3); + } + + return young; +} +EXPORT_SYMBOL(contpte_ptep_clear_flush_young); + +int contpte_ptep_set_access_flags(struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep, + pte_t entry, int dirty) +{ + pte_t orig_pte; + int i; + unsigned long start_addr; + + /* + * Gather the access/dirty bits for the contiguous range. If nothing has + * changed, its a noop. + */ + orig_pte = ptep_get(ptep); + if (pte_val(orig_pte) == pte_val(entry)) + return 0; + + /* + * We can fix up access/dirty bits without having to unfold/fold the + * contig range. But if the write bit is changing, we need to go through + * the full unfold/fold cycle. + */ + if (pte_write(orig_pte) == pte_write(entry)) { + /* + * For HW access management, we technically only need to update + * the flag on a single pte in the range. But for SW access + * management, we need to update all the ptes to prevent extra + * faults. Avoid per-page tlb flush in __ptep_set_access_flags() + * and instead flush the whole range at the end. + */ + ptep = contpte_align_down(ptep); + start_addr = addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); + + for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) + __ptep_set_access_flags(vma, addr, ptep, entry, 0); + + if (dirty) + __flush_tlb_range(vma, start_addr, addr, + PAGE_SIZE, true, 3); + } else { + __contpte_try_unfold(vma->vm_mm, addr, ptep, orig_pte); + __ptep_set_access_flags(vma, addr, ptep, entry, dirty); + contpte_try_fold(vma->vm_mm, addr, ptep, entry); + } + + return 1; +} +EXPORT_SYMBOL(contpte_ptep_set_access_flags);
With the ptep API sufficiently refactored, we can now introduce a new "contpte" API layer, which transparently manages the PTE_CONT bit for user mappings. Whenever it detects a set of PTEs that meet the requirements for a contiguous range, the PTEs are re-painted with the PTE_CONT bit. Use of contpte mappings is intended to be transparent to the core-mm, which continues to interact with individual ptes. Since a contpte block only has a single access and dirty bit, the semantic here changes slightly; when getting a pte (e.g. ptep_get()) that is part of a contpte mapping, the access and dirty information are pulled from the block (so all ptes in the block return the same access/dirty info). When changing the access/dirty info on a pte (e.g. ptep_set_access_flags()) that is part of a contpte mapping, this change will affect the whole contpte block. This is works fine in practice since we guarrantee that only a single folio is mapped by a contpte block, and the core-mm tracks access/dirty information per folio. This initial change provides a baseline that can be optimized in future commits. That said, fold/unfold operations (which imply tlb invalidation) are avoided where possible with a few tricks for access/dirty bit management. Write-protect modifications for contpte mappings are currently non-optimal, and incure a regression in fork() performance. This will be addressed in follow-up changes. In order for the public functions, which used to be pure inline, to continue to be callable by modules, export all the contpte_* symbols that are now called by those public inline functions. The feature is enabled/disabled with the ARM64_CONTPTE Kconfig parameter at build time. It defaults to enabled as long as its dependency, TRANSPARENT_HUGEPAGE is also enabled. The core-mm depends upon TRANSPARENT_HUGEPAGE to be able to allocate large folios, so if its not enabled, then there is no chance of meeting the physical contiguity requirement for contpte mappings. Signed-off-by: Ryan Roberts <ryan.roberts@arm.com> --- arch/arm64/Kconfig | 10 +- arch/arm64/include/asm/pgtable.h | 202 ++++++++++++++++++ arch/arm64/mm/Makefile | 1 + arch/arm64/mm/contpte.c | 351 +++++++++++++++++++++++++++++++ 4 files changed, 563 insertions(+), 1 deletion(-) create mode 100644 arch/arm64/mm/contpte.c