[PATCH 07/12] huge_memory: Allow mappings of PMD sized pages

Alistair Popple
2024-09-10T04:24:13Z

Currently DAX folio/page reference counts are managed differently to
normal pages. To allow these to be managed the same as normal pages
introduce dax_insert_pfn_pmd. This will map the entire PMD-sized folio
and take references as it would for a normally mapped page.

This is distinct from the current mechanism, vmf_insert_pfn_pmd, which
simply inserts a special devmap PMD entry into the page table without
holding a reference to the page for the mapping.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
include/linux/huge_mm.h | 1 +-
mm/huge_memory.c | 57 ++++++++++++++++++++++++++++++++++--------
2 files changed, 48 insertions(+), 10 deletions(-)

diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index d3a1872..eaf3f78 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -40,6 +40,7 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,

vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write);
vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write);
+vm_fault_t dax_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write);
vm_fault_t dax_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write);

enum transparent_hugepage_flag {
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e8985a4..790041e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1237,14 +1237,12 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
{
struct mm_struct *mm = vma->vm_mm;
pmd_t entry;
- spinlock_t *ptl;

- ptl = pmd_lock(mm, pmd);
if (!pmd_none(*pmd)) {
if (write) {
if (pmd_pfn(*pmd) != pfn_t_to_pfn(pfn)) {
WARN_ON_ONCE(!is_huge_zero_pmd(*pmd));
- goto out_unlock;
+ return;
}
entry = pmd_mkyoung(*pmd);
entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
@@ -1252,7 +1250,7 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
update_mmu_cache_pmd(vma, addr, pmd);
}

- goto out_unlock;
+ return;
}

entry = pmd_mkhuge(pfn_t_pmd(pfn, prot));
@@ -1271,11 +1269,6 @@ static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,

set_pmd_at(mm, addr, pmd, entry);
update_mmu_cache_pmd(vma, addr, pmd);
-
-out_unlock:
- spin_unlock(ptl);
- if (pgtable)
- pte_free(mm, pgtable);
}

/**
@@ -1294,6 +1287,7 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write)
struct vm_area_struct *vma = vmf->vma;
pgprot_t pgprot = vma->vm_page_prot;
pgtable_t pgtable = NULL;
+ spinlock_t *ptl;

/*
* If we had pmd_special, we could avoid all these restrictions,
@@ -1316,12 +1310,55 @@ vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write)
}

track_pfn_insert(vma, &pgprot, pfn);
-
+ ptl = pmd_lock(vma->vm_mm, vmf->pmd);
insert_pfn_pmd(vma, addr, vmf->pmd, pfn, pgprot, write, pgtable);
+ spin_unlock(ptl);
+ if (pgtable)
+ pte_free(vma->vm_mm, pgtable);
+
return VM_FAULT_NOPAGE;
}
EXPORT_SYMBOL_GPL(vmf_insert_pfn_pmd);

+vm_fault_t dax_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, bool write)
+{
+ struct vm_area_struct *vma = vmf->vma;
+ unsigned long addr = vmf->address & PMD_MASK;
+ struct mm_struct *mm = vma->vm_mm;
+ spinlock_t *ptl;
+ pgtable_t pgtable = NULL;
+ struct folio *folio;
+ struct page *page;
+
+ if (addr < vma->vm_start || addr >= vma->vm_end)
+ return VM_FAULT_SIGBUS;
+
+ if (arch_needs_pgtable_deposit()) {
+ pgtable = pte_alloc_one(vma->vm_mm);
+ if (!pgtable)
+ return VM_FAULT_OOM;
+ }
+
+ track_pfn_insert(vma, &vma->vm_page_prot, pfn);
+
+ ptl = pmd_lock(mm, vmf->pmd);
+ if (pmd_none(*vmf->pmd)) {
+ page = pfn_t_to_page(pfn);
+ folio = page_folio(page);
+ folio_get(folio);
+ folio_add_file_rmap_pmd(folio, page, vma);
+ add_mm_counter(mm, mm_counter_file(folio), HPAGE_PMD_NR);
+ }
+ insert_pfn_pmd(vma, addr, vmf->pmd, pfn, vma->vm_page_prot,
+ write, pgtable);
+ spin_unlock(ptl);
+ if (pgtable)
+ pte_free(mm, pgtable);
+
+ return VM_FAULT_NOPAGE;
+}
+EXPORT_SYMBOL_GPL(dax_insert_pfn_pmd);
+
#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
static pud_t maybe_pud_mkwrite(pud_t pud, struct vm_area_struct *vma)
{
--
git-series 0.9.1