[HMM v13 06/18] mm/ZONE_DEVICE/unaddressable: add special swap for unaddressable

["Jérôme Glisse" <jglisse@redhat.com>]

To allow use of device un-addressable memory inside a process add a
special swap type. Also add a new callback to handle page fault on
such entry.

Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/proc/task_mmu.c       | 10 +++++++-
 include/linux/memremap.h |  5 ++++
 include/linux/swap.h     | 18 ++++++++++---
 include/linux/swapops.h  | 67 ++++++++++++++++++++++++++++++++++++++++++++++++
 kernel/memremap.c        | 14 ++++++++++
 mm/Kconfig               | 12 +++++++++
 mm/memory.c              | 24 +++++++++++++++++
 mm/mprotect.c            | 12 +++++++++
 8 files changed, 158 insertions(+), 4 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 6909582..0726d39 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -544,8 +544,11 @@ static void smaps_pte_entry(pte_t *pte, unsigned long addr,
 			} else {
 				mss->swap_pss += (u64)PAGE_SIZE << PSS_SHIFT;
 			}
-		} else if (is_migration_entry(swpent))
+		} else if (is_migration_entry(swpent)) {
 			page = migration_entry_to_page(swpent);
+		} else if (is_device_entry(swpent)) {
+			page = device_entry_to_page(swpent);
+		}
 	} else if (unlikely(IS_ENABLED(CONFIG_SHMEM) && mss->check_shmem_swap
 							&& pte_none(*pte))) {
 		page = find_get_entry(vma->vm_file->f_mapping,
@@ -708,6 +711,8 @@ static int smaps_hugetlb_range(pte_t *pte, unsigned long hmask,
 
 		if (is_migration_entry(swpent))
 			page = migration_entry_to_page(swpent);
+		if (is_device_entry(swpent))
+			page = device_entry_to_page(swpent);
 	}
 	if (page) {
 		int mapcount = page_mapcount(page);
@@ -1191,6 +1196,9 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm,
 		flags |= PM_SWAP;
 		if (is_migration_entry(entry))
 			page = migration_entry_to_page(entry);
+
+		if (is_device_entry(entry))
+			page = device_entry_to_page(entry);
 	}
 
 	if (page && !PageAnon(page))
diff --git a/include/linux/memremap.h b/include/linux/memremap.h
index b6f03e9..d584c74 100644
--- a/include/linux/memremap.h
+++ b/include/linux/memremap.h
@@ -47,6 +47,11 @@ static inline struct vmem_altmap *to_vmem_altmap(unsigned long memmap_start)
  */
 struct dev_pagemap {
 	void (*free_devpage)(struct page *page, void *data);
+	int (*fault)(struct vm_area_struct *vma,
+		     unsigned long addr,
+		     struct page *page,
+		     unsigned flags,
+		     pmd_t *pmdp);
 	struct vmem_altmap *altmap;
 	const struct resource *res;
 	struct percpu_ref *ref;
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 7e553e1..599cb54 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -50,6 +50,17 @@ static inline int current_is_kswapd(void)
  */
 
 /*
+ * Un-addressable device memory support
+ */
+#ifdef CONFIG_DEVICE_UNADDRESSABLE
+#define SWP_DEVICE_NUM 2
+#define SWP_DEVICE_WRITE (MAX_SWAPFILES + SWP_HWPOISON_NUM + SWP_MIGRATION_NUM)
+#define SWP_DEVICE (MAX_SWAPFILES + SWP_HWPOISON_NUM + SWP_MIGRATION_NUM + 1)
+#else
+#define SWP_DEVICE_NUM 0
+#endif
+
+/*
  * NUMA node memory migration support
  */
 #ifdef CONFIG_MIGRATION
@@ -71,7 +82,8 @@ static inline int current_is_kswapd(void)
 #endif
 
 #define MAX_SWAPFILES \
-	((1 << MAX_SWAPFILES_SHIFT) - SWP_MIGRATION_NUM - SWP_HWPOISON_NUM)
+	((1 << MAX_SWAPFILES_SHIFT) - SWP_DEVICE_NUM - \
+	SWP_MIGRATION_NUM - SWP_HWPOISON_NUM)
 
 /*
  * Magic header for a swap area. The first part of the union is
@@ -442,8 +454,8 @@ static inline void show_swap_cache_info(void)
 {
 }
 
-#define free_swap_and_cache(swp)	is_migration_entry(swp)
-#define swapcache_prepare(swp)		is_migration_entry(swp)
+#define free_swap_and_cache(e) (is_migration_entry(e) || is_device_entry(e))
+#define swapcache_prepare(e) (is_migration_entry(e) || is_device_entry(e))
 
 static inline int add_swap_count_continuation(swp_entry_t swp, gfp_t gfp_mask)
 {
diff --git a/include/linux/swapops.h b/include/linux/swapops.h
index 5c3a5f3..d1aa425 100644
--- a/include/linux/swapops.h
+++ b/include/linux/swapops.h
@@ -100,6 +100,73 @@ static inline void *swp_to_radix_entry(swp_entry_t entry)
 	return (void *)(value | RADIX_TREE_EXCEPTIONAL_ENTRY);
 }
 
+#ifdef CONFIG_DEVICE_UNADDRESSABLE
+static inline swp_entry_t make_device_entry(struct page *page, bool write)
+{
+	return swp_entry(write?SWP_DEVICE_WRITE:SWP_DEVICE, page_to_pfn(page));
+}
+
+static inline bool is_device_entry(swp_entry_t entry)
+{
+	int type = swp_type(entry);
+	return type == SWP_DEVICE || type == SWP_DEVICE_WRITE;
+}
+
+static inline void make_device_entry_read(swp_entry_t *entry)
+{
+	*entry = swp_entry(SWP_DEVICE, swp_offset(*entry));
+}
+
+static inline bool is_write_device_entry(swp_entry_t entry)
+{
+	return unlikely(swp_type(entry) == SWP_DEVICE_WRITE);
+}
+
+static inline struct page *device_entry_to_page(swp_entry_t entry)
+{
+	return pfn_to_page(swp_offset(entry));
+}
+
+int device_entry_fault(struct vm_area_struct *vma,
+		       unsigned long addr,
+		       swp_entry_t entry,
+		       unsigned flags,
+		       pmd_t *pmdp);
+#else /* CONFIG_DEVICE_UNADDRESSABLE */
+static inline swp_entry_t make_device_entry(struct page *page, bool write)
+{
+	return swp_entry(0, 0);
+}
+
+static inline void make_device_entry_read(swp_entry_t *entry)
+{
+}
+
+static inline bool is_device_entry(swp_entry_t entry)
+{
+	return false;
+}
+
+static inline bool is_write_device_entry(swp_entry_t entry)
+{
+	return false;
+}
+
+static inline struct page *device_entry_to_page(swp_entry_t entry)
+{
+	return NULL;
+}
+
+static inline int device_entry_fault(struct vm_area_struct *vma,
+				     unsigned long addr,
+				     swp_entry_t entry,
+				     unsigned flags,
+				     pmd_t *pmdp)
+{
+	return VM_FAULT_SIGBUS;
+}
+#endif /* CONFIG_DEVICE_UNADDRESSABLE */
+
 #ifdef CONFIG_MIGRATION
 static inline swp_entry_t make_migration_entry(struct page *page, int write)
 {
diff --git a/kernel/memremap.c b/kernel/memremap.c
index cf83928..0670015 100644
--- a/kernel/memremap.c
+++ b/kernel/memremap.c
@@ -18,6 +18,8 @@
 #include <linux/io.h>
 #include <linux/mm.h>
 #include <linux/memory_hotplug.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
 
 #ifndef ioremap_cache
 /* temporary while we convert existing ioremap_cache users to memremap */
@@ -200,6 +202,18 @@ void put_zone_device_page(struct page *page)
 }
 EXPORT_SYMBOL(put_zone_device_page);
 
+int device_entry_fault(struct vm_area_struct *vma,
+		       unsigned long addr,
+		       swp_entry_t entry,
+		       unsigned flags,
+		       pmd_t *pmdp)
+{
+	struct page *page = device_entry_to_page(entry);
+
+	return page->pgmap->fault(vma, addr, page, flags, pmdp);
+}
+EXPORT_SYMBOL(device_entry_fault);
+
 static void pgmap_radix_release(struct resource *res)
 {
 	resource_size_t key, align_start, align_size, align_end;
diff --git a/mm/Kconfig b/mm/Kconfig
index be0ee11..0a21411 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -704,6 +704,18 @@ config ZONE_DEVICE
 
 	  If FS_DAX is enabled, then say Y.
 
+config DEVICE_UNADDRESSABLE
+	bool "Un-addressable device memory (GPU memory, ...)"
+	depends on ZONE_DEVICE
+
+	help
+	  Allow to create struct page for un-addressable device memory
+	  ie memory that is only accessible by the device (or group of
+	  devices).
+
+	  This allow to migrate chunk of process memory to device memory
+	  while that memory is use by the device.
+
 config FRAME_VECTOR
 	bool
 
diff --git a/mm/memory.c b/mm/memory.c
index 15f2908..a83d690 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -889,6 +889,21 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 					pte = pte_swp_mksoft_dirty(pte);
 				set_pte_at(src_mm, addr, src_pte, pte);
 			}
+		} else if (is_device_entry(entry)) {
+			page = device_entry_to_page(entry);
+
+			get_page(page);
+			rss[mm_counter(page)]++;
+			page_dup_rmap(page, false);
+
+			if (is_write_device_entry(entry) &&
+			    is_cow_mapping(vm_flags)) {
+				make_device_entry_read(&entry);
+				pte = swp_entry_to_pte(entry);
+				if (pte_swp_soft_dirty(*src_pte))
+					pte = pte_swp_mksoft_dirty(pte);
+				set_pte_at(src_mm, addr, src_pte, pte);
+			}
 		}
 		goto out_set_pte;
 	}
@@ -1191,6 +1206,12 @@ again:
 
 			page = migration_entry_to_page(entry);
 			rss[mm_counter(page)]--;
+		} else if (is_device_entry(entry)) {
+			struct page *page = device_entry_to_page(entry);
+			rss[mm_counter(page)]--;
+
+			page_remove_rmap(page, false);
+			put_page(page);
 		}
 		if (unlikely(!free_swap_and_cache(entry)))
 			print_bad_pte(vma, addr, ptent, NULL);
@@ -2536,6 +2557,9 @@ int do_swap_page(struct fault_env *fe, pte_t orig_pte)
 	if (unlikely(non_swap_entry(entry))) {
 		if (is_migration_entry(entry)) {
 			migration_entry_wait(vma->vm_mm, fe->pmd, fe->address);
+		} else if (is_device_entry(entry)) {
+			ret = device_entry_fault(vma, fe->address, entry,
+						 fe->flags, fe->pmd);
 		} else if (is_hwpoison_entry(entry)) {
 			ret = VM_FAULT_HWPOISON;
 		} else {
diff --git a/mm/mprotect.c b/mm/mprotect.c
index 1bc1eb3..70aff3a 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -139,6 +139,18 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
 
 				pages++;
 			}
+
+			if (is_write_device_entry(entry)) {
+				pte_t newpte;
+
+				make_device_entry_read(&entry);
+				newpte = swp_entry_to_pte(entry);
+				if (pte_swp_soft_dirty(oldpte))
+					newpte = pte_swp_mksoft_dirty(newpte);
+				set_pte_at(mm, addr, pte, newpte);
+
+				pages++;
+			}
 		}
 	} while (pte++, addr += PAGE_SIZE, addr != end);
 	arch_leave_lazy_mmu_mode();
-- 
2.4.3