[PATCH v2 03/15] riscv/mm: implement Svnapot contpte read-side helpers
Yunhui Cui
cuiyunhui at bytedance.com
Thu Jul 16 05:41:38 PDT 2026
Svnapot keeps a contiguous mapping encoded in a block of page-table
entries, while generic MM code expects the public PTE getters to return
a normal per-page view for the address being queried. Without a dedicated
read path, exposing the raw NAPOT encoding through the public helpers
would leak arch-private representation details into generic MM users and
make folded mappings harder to integrate with existing PTE walkers.
Add Svnapot-aware contpte read-side helpers and route the public PTE
getters through them, so generic MM sees the logical sub-PTE for the
current page while RISC-V raw helpers continue to operate on the encoded
entries.
Signed-off-by: Yunhui Cui <cuiyunhui at bytedance.com>
---
arch/riscv/include/asm/pgtable.h | 50 +++++-
arch/riscv/mm/Makefile | 1 +
arch/riscv/mm/contpte.c | 273 +++++++++++++++++++++++++++++++
3 files changed, 322 insertions(+), 2 deletions(-)
create mode 100644 arch/riscv/mm/contpte.c
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index a0f64e980e981..fce6d04ea65db 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -312,6 +312,11 @@ static inline unsigned long pte_napot(pte_t pte)
return 0;
}
+static inline pte_t pte_mknapot(pte_t pte, unsigned int order)
+{
+ return pte;
+}
+
#endif /* CONFIG_RISCV_ISA_SVNAPOT */
/* Yields the page frame number (PFN) of a page table entry */
@@ -350,6 +355,11 @@ static inline int pte_present(pte_t pte)
return (pte_val(pte) & (_PAGE_PRESENT | _PAGE_PROT_NONE));
}
+static inline bool pte_present_napot(pte_t pte)
+{
+ return pte_present(pte) && pte_napot(pte);
+}
+
#define pte_accessible pte_accessible
static inline unsigned long pte_accessible(struct mm_struct *mm, pte_t a)
{
@@ -538,6 +548,13 @@ static inline pte_t pte_swp_clear_soft_dirty(pte_t pte)
#define pte_leaf_size(pte) (pte_napot(pte) ? \
napot_cont_size(napot_cont_order(pte)) :\
PAGE_SIZE)
+
+void __napotpte_try_fold(struct mm_struct *mm, unsigned long addr,
+ pte_t *ptep, pte_t pte);
+void __napotpte_try_unfold(struct mm_struct *mm, unsigned long addr,
+ pte_t *ptep, pte_t pte);
+pte_t napotpte_ptep_get(pte_t *ptep, pte_t orig_pte);
+pte_t napotpte_ptep_get_lockless(pte_t *ptep);
#endif
#ifdef CONFIG_ARCH_HAS_PTE_PROTNONE
@@ -689,6 +706,37 @@ static inline pte_t __ptep_get_lockless(pte_t *ptep)
return __ptep_get(ptep);
}
+#ifdef CONFIG_RISCV_ISA_SVNAPOT
+
+#define ptep_get ptep_get
+static inline pte_t ptep_get(pte_t *ptep)
+{
+ pte_t pte = __ptep_get(ptep);
+
+ if (likely(!pte_present_napot(pte)))
+ return pte;
+
+ return napotpte_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_lockless(ptep);
+
+ if (likely(!pte_present_napot(pte)))
+ return pte;
+
+ return napotpte_ptep_get_lockless(ptep);
+}
+
+#else
+
+#define ptep_get __ptep_get
+#define ptep_get_lockless __ptep_get_lockless
+
+#endif
+
static inline void __clear_young_dirty_pte(struct vm_area_struct *vma,
unsigned long addr, pte_t *ptep,
pte_t pte, cydp_t flags)
@@ -822,8 +870,6 @@ static inline bool __ptep_clear_flush_young(struct vm_area_struct *vma,
#define __ptep_clear_flush_young __ptep_clear_flush_young
-#define ptep_get __ptep_get
-#define ptep_get_lockless __ptep_get_lockless
#define set_pte __set_pte
#define set_ptes __set_ptes
diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
index b916a68d324ad..fd260903cd340 100644
--- a/arch/riscv/mm/Makefile
+++ b/arch/riscv/mm/Makefile
@@ -19,6 +19,7 @@ obj-y += context.o
obj-y += pmem.o
obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
+obj-$(CONFIG_RISCV_ISA_SVNAPOT) += contpte.o
obj-$(CONFIG_PTDUMP) += ptdump.o
obj-$(CONFIG_KASAN) += kasan_init.o
diff --git a/arch/riscv/mm/contpte.c b/arch/riscv/mm/contpte.c
new file mode 100644
index 0000000000000..43ea76e424492
--- /dev/null
+++ b/arch/riscv/mm/contpte.c
@@ -0,0 +1,273 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include <linux/align.h>
+#include <linux/cpufeature.h>
+#include <linux/efi.h>
+#include <linux/export.h>
+#include <linux/mm.h>
+#include <linux/mm_types.h>
+#include <linux/page_table_check.h>
+#include <linux/pgtable.h>
+
+#include <asm/tlbflush.h>
+
+static inline bool napot_hw_supported(void)
+{
+ return riscv_has_extension_unlikely(RISCV_ISA_EXT_SVNAPOT);
+}
+
+static inline bool mm_is_user(struct mm_struct *mm)
+{
+ if (unlikely(mm_is_efi(mm)))
+ return false;
+
+ return mm != &init_mm;
+}
+
+static inline unsigned int napotpte_order(void)
+{
+ return NAPOT_CONT64KB_ORDER;
+}
+
+static inline unsigned long napotpte_size(void)
+{
+ return napot_cont_size(napotpte_order());
+}
+
+static inline unsigned int napotpte_pte_num(void)
+{
+ return napot_pte_num(napotpte_order());
+}
+
+static inline unsigned long napot_align_addr(unsigned long addr)
+{
+ return ALIGN_DOWN(addr, napotpte_size());
+}
+
+static inline pte_t *napot_align_ptep(pte_t *ptep)
+{
+ return PTR_ALIGN_DOWN(ptep, napotpte_pte_num() * sizeof(*ptep));
+}
+
+static inline pte_t pte_mask_ad(pte_t pte)
+{
+ return pte_mkold(pte_mkclean(pte));
+}
+
+void __napotpte_try_unfold(struct mm_struct *mm, unsigned long addr,
+ pte_t *ptep, pte_t pte);
+
+static inline unsigned long pte_protval_no_pfn_no_napot(pte_t pte)
+{
+ return (pte_val(pte) & ~_PAGE_PFN_MASK) & ~_PAGE_NAPOT;
+}
+
+static inline pte_t napotpte_subpte(pte_t *ptep, pte_t pte)
+{
+ unsigned long pfn;
+ pgprot_t prot;
+
+ if (!pte_present_napot(pte))
+ return pte;
+
+ pfn = pte_pfn(pte) + (ptep - napot_align_ptep(ptep));
+ prot = __pgprot(pte_protval_no_pfn_no_napot(pte));
+
+ return pfn_pte(pfn, prot);
+}
+
+static inline pte_t __napot_ptep_get_and_clear(struct mm_struct *mm,
+ unsigned long addr, pte_t *ptep)
+{
+ pte_t pte;
+
+ pte = __pte(atomic_long_xchg((atomic_long_t *)ptep, 0));
+ page_table_check_pte_clear(mm, addr, pte_mknonnapot(pte, addr));
+
+ return pte;
+}
+
+static void napotpte_convert(struct mm_struct *mm, unsigned long addr,
+ pte_t *ptep, pte_t target)
+{
+ unsigned long start_addr, end, ptent_addr;
+ pte_t *start_ptep;
+ pte_t ptent, pte;
+ unsigned int i, nr;
+
+ start_addr = napot_align_addr(addr);
+ start_ptep = napot_align_ptep(ptep);
+ nr = napotpte_pte_num();
+ end = start_addr + napotpte_size();
+
+ for (i = 0; i < nr; i++) {
+ ptent_addr = start_addr + i * PAGE_SIZE;
+ ptent = __napot_ptep_get_and_clear(mm, ptent_addr,
+ start_ptep + i);
+ if (pte_dirty(ptent))
+ target = riscv_pte_mkhwdirty(target);
+ if (pte_young(ptent))
+ target = pte_mkyoung(target);
+ }
+
+ flush_tlb_mm_range(mm, start_addr, end, PAGE_SIZE);
+
+ page_table_check_ptes_set(mm, start_addr, start_ptep, target, nr);
+ if (pte_napot(target)) {
+ for (i = 0; i < nr; i++)
+ __set_pte_at(mm, start_ptep + i, target);
+ return;
+ }
+
+ for (i = 0; i < nr; i++) {
+ pte = pfn_pte(pte_pfn(target) + i,
+ __pgprot(pte_protval_no_pfn_no_napot(target)));
+ if (pte_dirty(target))
+ pte = riscv_pte_mkhwdirty(pte);
+ if (pte_young(target))
+ pte = pte_mkyoung(pte);
+ __set_pte_at(mm, start_ptep + i, pte);
+ }
+}
+
+static inline bool napotpte_is_consistent(pte_t pte, pte_t orig_pte)
+{
+ return pte_present_napot(pte) &&
+ pte_val(pte_mask_ad(pte)) == pte_val(pte_mask_ad(orig_pte));
+}
+
+void __napotpte_try_fold(struct mm_struct *mm, unsigned long addr,
+ pte_t *ptep, pte_t pte)
+{
+ struct page *page;
+ struct folio *folio;
+ unsigned long folio_start, folio_end;
+ unsigned long cont_start, cont_end;
+ unsigned long pfn;
+ pgprot_t prot;
+ pte_t expected, cur;
+ pte_t *start;
+ unsigned int i, nr;
+
+ if (!napot_hw_supported() || !mm_is_user(mm))
+ return;
+
+ if (!pte_present(pte) || pte_napot(pte) || pte_special(pte))
+ return;
+
+ /*
+ * Driver __GFP_COMP pages inserted by vm_insert_page() have valid
+ * compound metadata. Fold them only after verifying the whole supported
+ * Svnapot range is identical and contiguous.
+ */
+ page = pte_page(pte);
+ folio = page_folio(page);
+ folio_start = addr - (page - &folio->page) * PAGE_SIZE;
+ folio_end = folio_start + folio_nr_pages(folio) * PAGE_SIZE;
+ cont_start = napot_align_addr(addr);
+ cont_end = cont_start + napotpte_size();
+ if (folio_start > cont_start || folio_end < cont_end)
+ return;
+
+ nr = napotpte_pte_num();
+ start = napot_align_ptep(ptep);
+
+ pfn = ALIGN_DOWN(pte_pfn(pte), nr);
+ prot = pte_pgprot(pte_mask_ad(pte));
+ expected = pfn_pte(pfn, prot);
+
+ /*
+ * The caller must hold the PTL across validation and conversion.
+ * Software PTE updates are serialized by the PTL; hardware A/D updates
+ * may race and are re-read and folded into target by napotpte_convert().
+ */
+ for (i = 0; i < nr; i++) {
+ cur = READ_ONCE(start[i]);
+ if (pte_val(pte_mask_ad(cur)) != pte_val(expected))
+ return;
+ pte_val(expected) += 1UL << _PAGE_PFN_SHIFT;
+ }
+
+ expected = pte_mknapot(pfn_pte(pfn, prot), napotpte_order());
+ napotpte_convert(mm, addr, ptep, expected);
+}
+EXPORT_SYMBOL(__napotpte_try_fold);
+
+void __napotpte_try_unfold(struct mm_struct *mm, unsigned long addr,
+ pte_t *ptep, pte_t pte)
+{
+ pte_t target;
+ pgprot_t prot;
+
+ if (!napot_hw_supported() || !mm_is_user(mm) ||
+ !pte_present_napot(pte))
+ return;
+
+ prot = __pgprot(pte_protval_no_pfn_no_napot(pte));
+ target = pfn_pte(pte_pfn(pte), prot);
+
+ napotpte_convert(mm, addr, ptep, target);
+}
+EXPORT_SYMBOL(__napotpte_try_unfold);
+
+pte_t napotpte_ptep_get(pte_t *ptep, pte_t orig_pte)
+{
+ pte_t pte, cur;
+ pte_t *start;
+ unsigned int i, nr;
+
+ if (!napot_hw_supported() || !pte_present_napot(orig_pte))
+ return orig_pte;
+
+ pte = orig_pte;
+ start = napot_align_ptep(ptep);
+ nr = napotpte_pte_num();
+
+ for (i = 0; i < nr; i++) {
+ cur = READ_ONCE(start[i]);
+ if (!napotpte_is_consistent(cur, orig_pte))
+ return napotpte_subpte(ptep, orig_pte);
+ if (pte_dirty(cur))
+ pte = riscv_pte_mkhwdirty(pte);
+ if (pte_young(cur))
+ pte = pte_mkyoung(pte);
+ }
+
+ return napotpte_subpte(ptep, pte);
+}
+EXPORT_SYMBOL(napotpte_ptep_get);
+
+pte_t napotpte_ptep_get_lockless(pte_t *orig_ptep)
+{
+ pte_t orig_pte, pte;
+ pte_t *ptep;
+ unsigned int i, nr;
+
+ if (!napot_hw_supported())
+ return READ_ONCE(*orig_ptep);
+
+ nr = napotpte_pte_num();
+
+retry:
+ orig_pte = READ_ONCE(*orig_ptep);
+ if (!pte_present_napot(orig_pte))
+ return orig_pte;
+
+ ptep = napot_align_ptep(orig_ptep);
+
+ for (i = 0; i < nr; i++, ptep++) {
+ pte = READ_ONCE(*ptep);
+
+ if (!napotpte_is_consistent(pte, orig_pte))
+ goto retry;
+
+ if (pte_dirty(pte))
+ orig_pte = riscv_pte_mkhwdirty(orig_pte);
+
+ if (pte_young(pte))
+ orig_pte = pte_mkyoung(orig_pte);
+ }
+
+ return napotpte_subpte(orig_ptep, orig_pte);
+}
+EXPORT_SYMBOL(napotpte_ptep_get_lockless);
--
2.39.5
More information about the kvm-riscv
mailing list