[PATCH v12 28/29] HMM: CPU page fault on migrated memory.

From	Jérôme Glisse <jglisse@redhat.com>
Newsgroups	linux.kernel
Subject	[PATCH v12 28/29] HMM: CPU page fault on migrated memory.
Date	2016-03-08 21:00 +0100
Message-ID	<ravXs-5uX-17@gated-at.bofh.it> (permalink)
References	<ravNL-5ru-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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When CPU try to access memory that have been migrated to device memory
we have to copy it back to system memory. This patch implement the CPU
page fault handler for special HMM pte swap entry.

Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
---
 mm/hmm.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index 4dcd98f..38943a7 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -472,7 +472,59 @@ int hmm_handle_cpu_fault(struct mm_struct *mm,
 			pmd_t *pmdp, unsigned long addr,
 			unsigned flags, pte_t orig_pte)
 {
-	return VM_FAULT_SIGBUS;
+	unsigned long start, end;
+	struct hmm_event event;
+	swp_entry_t entry;
+	struct hmm *hmm;
+	dma_addr_t dst;
+	pte_t new_pte;
+	int ret;
+
+	/* First check for poisonous entry. */
+	entry = pte_to_swp_entry(orig_pte);
+	if (is_hmm_entry_poisonous(entry))
+		return VM_FAULT_SIGBUS;
+
+	hmm = hmm_ref(mm->hmm);
+	if (!hmm) {
+		pte_t poison = swp_entry_to_pte(make_hmm_entry_poisonous());
+		spinlock_t *ptl;
+		pte_t *ptep;
+
+		/* Check if cpu pte is already updated. */
+		ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
+		if (!pte_same(*ptep, orig_pte)) {
+			pte_unmap_unlock(ptep, ptl);
+			return 0;
+		}
+		set_pte_at(mm, addr, ptep, poison);
+		pte_unmap_unlock(ptep, ptl);
+		return VM_FAULT_SIGBUS;
+	}
+
+	/*
+	 * TODO we likely want to migrate more then one page at a time, we need
+	 * to call into the device driver to get good hint on the range to copy
+	 * back to system memory.
+	 *
+	 * For now just live with the one page at a time solution.
+	 */
+	start = addr & PAGE_MASK;
+	end = start + PAGE_SIZE;
+	hmm_event_init(&event, hmm, start, end, HMM_COPY_FROM_DEVICE);
+
+	ret = hmm_migrate_back(hmm, &event, mm, vma, &new_pte,
+			       &dst, start, end);
+	hmm_unref(hmm);
+	switch (ret) {
+	case 0:
+		return VM_FAULT_MAJOR;
+	case -ENOMEM:
+		return VM_FAULT_OOM;
+	case -EINVAL:
+	default:
+		return VM_FAULT_SIGBUS;
+	}
 }
 EXPORT_SYMBOL(hmm_handle_cpu_fault);
 
-- 
2.4.3

Thread

HMM (Heterogeneous Memory Management) Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 20:50 +0100
  [PATCH v12 11/29] HMM: add discard range helper (to clear and free resources for a range). Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 20:50 +0100
  [PATCH v12 19/29] HMM: add new HMM page table flag (select flag). Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 20:50 +0100
  [PATCH v12 03/29] mmu_notifier: pass page pointer to mmu_notifier_invalidate_page() v2 Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 20:50 +0100
  [PATCH v12 05/29] HMM: introduce heterogeneous memory management v5. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 20:50 +0100
  [PATCH v12 06/29] HMM: add HMM page table v4. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 20:50 +0100
  [PATCH v12 10/29] HMM: use CPU page table during invalidation. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 20:50 +0100
  [PATCH v12 29/29] HMM: add mirror fault support for system to device memory migration v3. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 20:50 +0100
  [PATCH v12 24/29] HMM: allow to get pointer to spinlock protecting a directory. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 20:50 +0100
  [PATCH v12 07/29] HMM: add per mirror page table v4. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 20:50 +0100
  [PATCH v12 15/29] HMM: add documentation explaining HMM internals and how to use it. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 20:50 +0100
  [PATCH v12 17/29] HMM: add special swap filetype for memory migrated to device v2. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 20:50 +0100
  [PATCH v12 21/29] HMM: mm add helper to update page table when migrating memory back v2. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 20:50 +0100
  [PATCH v12 23/29] HMM: new callback for copying memory from and to device memory v2. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 21:00 +0100
  [PATCH v12 13/29] HMM: DMA map memory on behalf of device driver v2. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 21:00 +0100
  [PATCH v12 14/29] HMM: Add support for hugetlb. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 21:00 +0100
  [PATCH v12 28/29] HMM: CPU page fault on migrated memory. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 21:00 +0100
  [PATCH v12 26/29] HMM: add helpers for migration back to system memory v3. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 21:00 +0100
  [PATCH v12 25/29] HMM: split DMA mapping function in two. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 21:00 +0100
  [PATCH v12 08/29] HMM: add device page fault support v6. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 21:00 +0100
  [PATCH v12 18/29] HMM: add new HMM page table flag (valid device memory). Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 21:00 +0100
  [PATCH v12 12/29] HMM: add dirty range helper (toggle dirty bit inside mirror page table) v2. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 21:00 +0100
  [PATCH v12 20/29] HMM: handle HMM device page table entry on mirror page table fault and update. Jérôme Glisse <jglisse@redhat.com> - 2016-03-08 21:00 +0100

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