[PATCH RFC v2 20/27] mm: hugepage: Handle huge page fault on access

Alexandru Elisei
2023-11-19T17:00:06Z

Handle PAGE_FAULT_ON_ACCESS faults for huge pages in a similar way to
regular pages.

Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
---
arch/arm64/include/asm/mte_tag_storage.h | 1 +
arch/arm64/include/asm/pgtable.h | 7 ++
arch/arm64/mm/fault.c | 81 ++++++++++++++++++++++++
include/linux/huge_mm.h | 2 +
include/linux/pgtable.h | 5 ++
mm/huge_memory.c | 4 +-
mm/memory.c | 3 +
7 files changed, 101 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/mte_tag_storage.h b/arch/arm64/include/asm/mte_tag_storage.h
index c70ced60a0cd..b97406d369ce 100644
--- a/arch/arm64/include/asm/mte_tag_storage.h
+++ b/arch/arm64/include/asm/mte_tag_storage.h
@@ -35,6 +35,7 @@ void free_tag_storage(struct page *page, int order);
bool page_tag_storage_reserved(struct page *page);

vm_fault_t handle_page_missing_tag_storage(struct vm_fault *vmf);
+vm_fault_t handle_huge_page_missing_tag_storage(struct vm_fault *vmf);
#else
static inline bool tag_storage_enabled(void)
{
diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 8cc135f1c112..1704411c096d 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -477,6 +477,13 @@ static inline vm_fault_t arch_do_page_fault_on_access(struct vm_fault *vmf)
return handle_page_missing_tag_storage(vmf);
return VM_FAULT_SIGBUS;
}
+
+static inline vm_fault_t arch_do_huge_page_fault_on_access(struct vm_fault *vmf)
+{
+ if (tag_storage_enabled())
+ return handle_huge_page_missing_tag_storage(vmf);
+ return VM_FAULT_SIGBUS;
+}
#endif /* CONFIG_ARCH_HAS_FAULT_ON_ACCESS */

#define pmd_present_invalid(pmd) (!!(pmd_val(pmd) & PMD_PRESENT_INVALID))
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index f5fa583acf18..6730a0812a24 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -1041,6 +1041,87 @@ vm_fault_t handle_page_missing_tag_storage(struct vm_fault *vmf)

return 0;

+out_retry:
+ put_page(page);
+ if (vmf->flags & FAULT_FLAG_VMA_LOCK)
+ vma_end_read(vma);
+ if (fault_flag_allow_retry_first(vmf->flags)) {
+ err = VM_FAULT_RETRY;
+ } else {
+ /* Replay the fault. */
+ err = 0;
+ }
+ return err;
+}
+
+vm_fault_t handle_huge_page_missing_tag_storage(struct vm_fault *vmf)
+{
+ unsigned long haddr = vmf->address & HPAGE_PMD_MASK;
+ struct vm_area_struct *vma = vmf->vma;
+ pmd_t old_pmd, new_pmd;
+ bool writable = false;
+ struct page *page;
+ vm_fault_t err;
+ int ret;
+
+ vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
+ if (unlikely(!pmd_same(vmf->orig_pmd, *vmf->pmd))) {
+ spin_unlock(vmf->ptl);
+ return 0;
+ }
+
+ old_pmd = vmf->orig_pmd;
+ new_pmd = pmd_modify(old_pmd, vma->vm_page_prot);
+
+ /*
+ * Detect now whether the PMD could be writable; this information
+ * is only valid while holding the PT lock.
+ */
+ writable = pmd_write(new_pmd);
+ if (!writable && vma_wants_manual_pte_write_upgrade(vma) &&
+ can_change_pmd_writable(vma, vmf->address, new_pmd))
+ writable = true;
+
+ page = vm_normal_page_pmd(vma, haddr, new_pmd);
+ if (!page)
+ goto out_map;
+
+ if (!(vma->vm_flags & VM_MTE))
+ goto out_map;
+
+ get_page(page);
+ vma_set_access_pid_bit(vma);
+
+ spin_unlock(vmf->ptl);
+ writable = false;
+
+ if (unlikely(is_migrate_isolate_page(page)))
+ goto out_retry;
+
+ ret = reserve_tag_storage(page, HPAGE_PMD_ORDER, GFP_HIGHUSER_MOVABLE);
+ if (ret)
+ goto out_retry;
+
+ put_page(page);
+
+ vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd);
+ if (unlikely(!pmd_same(old_pmd, *vmf->pmd))) {
+ spin_unlock(vmf->ptl);
+ return 0;
+ }
+
+out_map:
+ /* Restore the PMD */
+ new_pmd = pmd_modify(old_pmd, vma->vm_page_prot);
+ new_pmd = pmd_mkyoung(new_pmd);
+ if (writable)
+ new_pmd = pmd_mkwrite(new_pmd, vma);
+ set_pmd_at(vma->vm_mm, haddr, vmf->pmd, new_pmd);
+ update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
+ spin_unlock(vmf->ptl);
+
+ return 0;
+
out_retry:
put_page(page);
if (vmf->flags & FAULT_FLAG_VMA_LOCK)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index fa0350b0812a..bb84291f9231 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -36,6 +36,8 @@ bool move_huge_pmd(struct vm_area_struct *vma, unsigned long old_addr,
int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
pmd_t *pmd, unsigned long addr, pgprot_t newprot,
unsigned long cp_flags);
+bool can_change_pmd_writable(struct vm_area_struct *vma, unsigned long addr,
+ pmd_t pmd);

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);
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index e2c761dd6c41..de45f475bf8d 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1473,6 +1473,11 @@ static inline vm_fault_t arch_do_page_fault_on_access(struct vm_fault *vmf)
{
return VM_FAULT_SIGBUS;
}
+
+static inline vm_fault_t arch_do_huge_page_fault_on_access(struct vm_fault *vmf)
+{
+ return VM_FAULT_SIGBUS;
+}
#endif

#endif /* CONFIG_MMU */
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9beead961a65..d1402b43ea39 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1406,8 +1406,8 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf)
return VM_FAULT_FALLBACK;
}

-static inline bool can_change_pmd_writable(struct vm_area_struct *vma,
- unsigned long addr, pmd_t pmd)
+inline bool can_change_pmd_writable(struct vm_area_struct *vma,
+ unsigned long addr, pmd_t pmd)
{
struct page *page;

diff --git a/mm/memory.c b/mm/memory.c
index a04a971200b9..46b926625503 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5168,6 +5168,9 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
return 0;
}
if (pmd_trans_huge(vmf.orig_pmd) || pmd_devmap(vmf.orig_pmd)) {
+ if (fault_on_access_pmd(vmf.orig_pmd) && vma_is_accessible(vma))
+ return arch_do_huge_page_fault_on_access(&vmf);
+
if (pmd_protnone(vmf.orig_pmd) && vma_is_accessible(vma))
return do_huge_pmd_numa_page(&vmf);

--
2.42.1