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Subject[PATCH 08/14] vrange: Send SIGBUS when user try to access purged page
Date
From: Minchan Kim <minchan@kernel.org>

By vrange(2) semantic, a user should see SIGBUG if they try to
access purged page without marking the memory as non-voaltile
(ie, vrange(...VRANGE_NOVOLATILE)).

This allows for optimistic traversal of volatile pages, without
having to mark them non-volatile first and the SIGBUS allows
applications to trap and fixup the purged range before accessing
them again.

This patch implements it by adding SWP_VRANGE so it consumes one
from MAX_SWAPFILES. It means worst case of MAX_SWAPFILES in 32 bit
is 32 - 2 - 1 - 1 = 28. I think it's still enough for everybody.
If someone complains about that and thinks we shouldn't consume it,
I will change it with (swp_type 0, pgoffset 0) which is header of swap
which couldn't be allocated as swp_pte for swapout so we can use it.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Android Kernel Team <kernel-team@android.com>
Cc: Robert Love <rlove@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Neil Brown <neilb@suse.de>
Cc: Andrea Righi <andrea@betterlinux.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Mike Hommey <mh@glandium.org>
Cc: Taras Glek <tglek@mozilla.com>
Cc: Dhaval Giani <dhaval.giani@gmail.com>
Cc: Jan Kara <jack@suse.cz>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Cc: Michel Lespinasse <walken@google.com>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: linux-mm@kvack.org <linux-mm@kvack.org>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
include/linux/swap.h | 6 +++++-
include/linux/vrange.h | 20 ++++++++++++++++++++
mm/memory.c | 27 +++++++++++++++++++++++++++
mm/mincore.c | 5 ++++-
mm/vrange.c | 20 +++++++++++++++++++-
5 files changed, 75 insertions(+), 3 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index d95cde5..7fd1006 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -49,6 +49,9 @@ static inline int current_is_kswapd(void)
* actions on faults.
*/

+#define SWP_VRANGE_NUM 1
+#define SWP_VRANGE (MAX_SWAPFILES + SWP_HWPOISON_NUM + SWP_MIGRATION_NUM)
+
/*
* NUMA node memory migration support
*/
@@ -71,7 +74,8 @@ 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_MIGRATION_NUM - SWP_HWPOISON_NUM \
+ - SWP_VRANGE_NUM)

/*
* Magic header for a swap area. The first part of the union is
diff --git a/include/linux/vrange.h b/include/linux/vrange.h
index 778902d..50b9131 100644
--- a/include/linux/vrange.h
+++ b/include/linux/vrange.h
@@ -3,6 +3,8 @@

#include <linux/vrange_types.h>
#include <linux/mm.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>

#define vrange_from_node(node_ptr) \
container_of(node_ptr, struct vrange, node)
@@ -12,6 +14,16 @@

#ifdef CONFIG_MMU

+static inline swp_entry_t make_vrange_entry(void)
+{
+ return swp_entry(SWP_VRANGE, 0);
+}
+
+static inline int is_vrange_entry(swp_entry_t entry)
+{
+ return swp_type(entry) == SWP_VRANGE;
+}
+
static inline void vrange_root_init(struct vrange_root *vroot, int type,
void *object)
{
@@ -44,6 +56,9 @@ extern int vrange_fork(struct mm_struct *new,
int discard_vpage(struct page *page);
bool vrange_addr_volatile(struct vm_area_struct *vma, unsigned long addr);

+extern bool vrange_addr_purged(struct vm_area_struct *vma,
+ unsigned long address);
+
#else

static inline void vrange_root_init(struct vrange_root *vroot,
@@ -60,5 +75,10 @@ static inline bool vrange_addr_volatile(struct vm_area_struct *vma,
return false;
}
static inline int discard_vpage(struct page *page) { return 0 };
+static inline bool vrange_addr_purged(struct vm_area_struct *vma,
+ unsigned long address)
+{
+ return false;
+};
#endif
#endif /* _LINIUX_VRANGE_H */
diff --git a/mm/memory.c b/mm/memory.c
index af84bc0..e33dbce 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -59,6 +59,7 @@
#include <linux/gfp.h>
#include <linux/migrate.h>
#include <linux/string.h>
+#include <linux/vrange.h>

#include <asm/io.h>
#include <asm/pgalloc.h>
@@ -831,6 +832,8 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
if (unlikely(!pte_present(pte))) {
if (!pte_file(pte)) {
swp_entry_t entry = pte_to_swp_entry(pte);
+ if (is_vrange_entry(entry))
+ goto out_set_pte;

if (swap_duplicate(entry) < 0)
return entry.val;
@@ -1174,6 +1177,8 @@ again:
print_bad_pte(vma, addr, ptent, NULL);
} else {
swp_entry_t entry = pte_to_swp_entry(ptent);
+ if (is_vrange_entry(entry))
+ goto out;

if (!non_swap_entry(entry))
rss[MM_SWAPENTS]--;
@@ -1190,6 +1195,7 @@ again:
if (unlikely(!free_swap_and_cache(entry)))
print_bad_pte(vma, addr, ptent, NULL);
}
+out:
pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
} while (pte++, addr += PAGE_SIZE, addr != end);

@@ -3715,15 +3721,36 @@ int handle_pte_fault(struct mm_struct *mm,

entry = *pte;
if (!pte_present(entry)) {
+ swp_entry_t vrange_entry;
+
if (pte_none(entry)) {
if (vma->vm_ops) {
if (likely(vma->vm_ops->fault))
return do_linear_fault(mm, vma, address,
pte, pmd, flags, entry);
}
+anon:
return do_anonymous_page(mm, vma, address,
pte, pmd, flags);
}
+
+ vrange_entry = pte_to_swp_entry(entry);
+ if (unlikely(is_vrange_entry(vrange_entry))) {
+ if (!vrange_addr_purged(vma, address)) {
+ /* zap pte */
+ ptl = pte_lockptr(mm, pmd);
+ spin_lock(ptl);
+ if (unlikely(!pte_same(*pte, entry)))
+ goto unlock;
+ flush_cache_page(vma, address, pte_pfn(*pte));
+ ptep_clear_flush(vma, address, pte);
+ pte_unmap_unlock(pte, ptl);
+ goto anon;
+ }
+
+ return VM_FAULT_SIGBUS;
+ }
+
if (pte_file(entry))
return do_nonlinear_fault(mm, vma, address,
pte, pmd, flags, entry);
diff --git a/mm/mincore.c b/mm/mincore.c
index da2be56..2a95eef 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -15,6 +15,7 @@
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/hugetlb.h>
+#include <linux/vrange.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>
@@ -129,7 +130,9 @@ static void mincore_pte_range(struct vm_area_struct *vma, pmd_t *pmd,
} else { /* pte is a swap entry */
swp_entry_t entry = pte_to_swp_entry(pte);

- if (is_migration_entry(entry)) {
+ if (is_vrange_entry(entry))
+ *vec = 0;
+ else if (is_migration_entry(entry)) {
/* migration entries are always uptodate */
*vec = 1;
} else {
diff --git a/mm/vrange.c b/mm/vrange.c
index c72e72d..c19a966 100644
--- a/mm/vrange.c
+++ b/mm/vrange.c
@@ -10,7 +10,6 @@
#include <linux/rmap.h>
#include <linux/hugetlb.h>
#include "internal.h"
-#include <linux/swap.h>
#include <linux/mmu_notifier.h>

static struct kmem_cache *vrange_cachep;
@@ -430,6 +429,24 @@ bool vrange_addr_volatile(struct vm_area_struct *vma, unsigned long addr)
return ret;
}

+bool vrange_addr_purged(struct vm_area_struct *vma, unsigned long addr)
+{
+ struct vrange_root *vroot;
+ struct vrange *range;
+ unsigned long vstart_idx;
+ bool ret = false;
+
+ vroot = __vma_to_vroot(vma);
+ vstart_idx = __vma_addr_to_index(vma, addr);
+
+ vrange_lock(vroot);
+ range = __vrange_find(vroot, vstart_idx, vstart_idx + PAGE_SIZE - 1);
+ if (range && range->purged)
+ ret = true;
+ vrange_unlock(vroot);
+ return ret;
+}
+
/* Caller should hold vrange_lock */
static void do_purge(struct vrange_root *vroot,
unsigned long start_idx, unsigned long end_idx)
@@ -473,6 +490,7 @@ static void try_to_discard_one(struct vrange_root *vroot, struct page *page,
page_remove_rmap(page);
page_cache_release(page);

+ set_pte_at(mm, addr, pte, swp_entry_to_pte(make_vrange_entry()));
pte_unmap_unlock(pte, ptl);
mmu_notifier_invalidate_page(mm, addr);

--
1.8.1.2


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