Re: [PATCH v4 14/16] arm64/mm: Wire up PTE_CONT for user mappings
From: Alexandre Ghiti
Date: Mon Jan 15 2024 - 16:23:46 EST
On 15/01/2024 17:27, Ryan Roberts wrote:
On 15/01/2024 15:14, Alexandre Ghiti wrote:
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@xxxxxxxxxx>
Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
---
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?
entry doesn't have PTE_CONT bit set, that's correct. I intentionally strip that
bit at the interface boundary, because it is the implementation's job to decide
whether its a contpte block, not the caller's. But there are situations where
the caller can end up with a pte that has PTE_CONT set (by having done a
previous ptep_get() for example) and then it forwards the pte to a setter. So
stripping it is required; It would probably be cleaner to strip it before
returning it from ptep_get(), but that would be problematic for pte_leaf_size()
which is called from perf_get_pgtable_size().
In this particular case, __ptep_set_access_flags() only modifies the PTE's
access flags, so CONT_PTE will remain as it is in the page table. The fact that
entry has it cleared is not a problem.
I see, I had not checked the arm64 implementation of
ptep_set_access_flags(). For context, I'm merging the arm64 contpte
support with the riscv napot support, the implementation being quite
similar (although riscv is a bit different as it uses bits from the pfn
to advertise the number of contiguous ptes).
Anyway, our implementation of ptep_set_access_flags() actually sets the
ptep with entry, so we would actually lose the cont bit. I would simply
do the following (I will in my patchset, no need for you to worry about
this):
__ptep_set_access_flags(vma, addr, ptep, pte_mkcont(entry), 0);
Let me know if you think this is not right,
Thanks,
Alex
Thanks,
Ryan
+
+ 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);