[PATCH v4 14/16] arm64/mm: Wire up PTE_CONT for user mappings
Alexandre Ghiti
alex at ghiti.fr
Mon Jan 15 07:14:18 PST 2024
Hi Ryan,
On 18/12/2023 11:50, Ryan Roberts wrote:
> 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 guarantee 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.
>
> Tested-by: John Hubbard <jhubbard at nvidia.com>
> Signed-off-by: Ryan Roberts <ryan.roberts at arm.com>
> ---
> arch/arm64/Kconfig | 10 +-
> arch/arm64/include/asm/pgtable.h | 184 +++++++++++++++
> arch/arm64/mm/Makefile | 1 +
> arch/arm64/mm/contpte.c | 388 +++++++++++++++++++++++++++++++
> 4 files changed, 582 insertions(+), 1 deletion(-)
> create mode 100644 arch/arm64/mm/contpte.c
>
> 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..e64120452301 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 +1120,184 @@ 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 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.
> + */
> +
> + const unsigned long contmask = CONT_PTES - 1;
> + bool valign = (((unsigned long)ptep >> 3) & contmask) == contmask;
> + bool palign = (pte_pfn(pte) & contmask) == contmask;
> +
> + if (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 (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 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 (nr == 1) {
> + contpte_try_unfold(mm, addr, ptep, __ptep_get(ptep));
> + __set_ptes(mm, addr, ptep, pte, 1);
> + 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 +1313,8 @@ 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..69c36749dd98
> --- /dev/null
> +++ b/arch/arm64/mm/contpte.c
> @@ -0,0 +1,388 @@
> +// 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 inline bool mm_is_user(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 pte_t *contpte_align_down(pte_t *ptep)
> +{
> + return (pte_t *)(ALIGN_DOWN((unsigned long)ptep >> 3, CONT_PTES) << 3);
> +}
> +
> +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_convert(struct mm_struct *mm, unsigned long addr,
> + pte_t *ptep, pte_t pte)
> +{
> + 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));
> +
> + 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.
> + */
> +
> + unsigned long folio_saddr;
> + unsigned long folio_eaddr;
> + unsigned long cont_saddr;
> + unsigned long cont_eaddr;
> + struct folio *folio;
> + struct page *page;
> + unsigned long pfn;
> + pte_t *orig_ptep;
> + pgprot_t prot;
> + pte_t subpte;
> + int i;
> +
> + if (!mm_is_user(mm))
> + return;
> +
> + page = pte_page(pte);
> + folio = page_folio(page);
> + folio_saddr = addr - (page - &folio->page) * PAGE_SIZE;
> + folio_eaddr = folio_saddr + folio_nr_pages(folio) * PAGE_SIZE;
> + cont_saddr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
> + cont_eaddr = cont_saddr + CONT_PTE_SIZE;
> +
> + 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;
> + }
> +
> + pte = pte_mkcont(pte);
> + contpte_convert(mm, addr, orig_ptep, pte);
> +}
> +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 just check that the mm is user space.
> + */
> +
> + if (!mm_is_user(mm))
> + return;
> +
> + pte = pte_mknoncont(pte);
> + contpte_convert(mm, addr, ptep, pte);
> +}
> +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.
> + */
> +
> + pgprot_t orig_prot;
> + unsigned long pfn;
> + pte_t orig_pte;
> + pgprot_t prot;
> + pte_t *ptep;
> + pte_t pte;
> + 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;
> + unsigned long pfn;
> + pgprot_t prot;
> + pte_t orig_pte;
> +
> + if (!mm_is_user(mm))
> + return __set_ptes(mm, addr, ptep, pte, nr);
> +
> + end = addr + (nr << PAGE_SHIFT);
> + pfn = pte_pfn(pte);
> + prot = pte_pgprot(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 young = 0;
> + int i;
> +
> + 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)
> +{
> + unsigned long start_addr;
> + pte_t orig_pte;
> + int i;
> +
> + /*
> + * Gather the access/dirty bits for the contiguous range. If nothing has
> + * changed, its a noop.
> + */
> + orig_pte = pte_mknoncont(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);
entry was pte_mknoncont() in ptep_set_access_flags() so here you lose
the contpte range, is that intentional? Or am I mistaken?
> +
> + 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);
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