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Message-Id: <1367870221-12676-2-git-send-email-aarcange@redhat.com>
Date: Mon, 6 May 2013 21:56:58 +0200
From: Andrea Arcangeli <aarcange@...hat.com>
To: qemu-devel@...gnu.org, linux-kernel@...r.kernel.org
Cc: Isaku Yamahata <yamahata@...inux.co.jp>,
Juan Quintela <quintela@...hat.com>,
Orit Wasserman <owasserm@...hat.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Anthony Liguori <aliguori@...ibm.com>,
Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
Hugh Dickins <hughd@...gle.com>
Subject: [PATCH 1/4] mm: madvise MADV_USERFAULT
MADV_USERFAULT is a new madvise flag that will set VM_USERFAULT in the
vma flags. Whenever VM_USERFAULT is set in an anonymous vma, if
userland touches a still unmapped virtual address, a sigbus signal is
sent instead of allocating a new page. The sigbus signal handler will
then resolve the page fault in userland by calling the remap_anon_pages
syscall.
This functionality is needed to reliably implement postcopy live
migration in KVM (without having to use a special chardevice that
would disable all advanced Linux VM features, like swapping, KSM, THP,
automatic NUMA balancing, etc...).
MADV_USERFAULT could also be used to offload parts of anonymous memory
regions to remote nodes or to implement network distributed shared
memory.
Here I enlarged the vm_flags to 64bit as we run out of bits (noop on
64bit kernels). An alternative is to find some combination of flags
that are mutually exclusive if set.
Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
---
arch/alpha/include/uapi/asm/mman.h | 3 +++
arch/mips/include/uapi/asm/mman.h | 3 +++
arch/parisc/include/uapi/asm/mman.h | 3 +++
arch/xtensa/include/uapi/asm/mman.h | 3 +++
include/linux/mm.h | 1 +
include/linux/mm_types.h | 2 +-
include/uapi/asm-generic/mman-common.h | 3 +++
mm/huge_memory.c | 34 ++++++++++++++++++++++++----------
mm/madvise.c | 16 ++++++++++++++++
mm/memory.c | 10 ++++++++++
10 files changed, 67 insertions(+), 11 deletions(-)
diff --git a/arch/alpha/include/uapi/asm/mman.h b/arch/alpha/include/uapi/asm/mman.h
index 0086b47..a10313c 100644
--- a/arch/alpha/include/uapi/asm/mman.h
+++ b/arch/alpha/include/uapi/asm/mman.h
@@ -60,6 +60,9 @@
overrides the coredump filter bits */
#define MADV_DODUMP 17 /* Clear the MADV_NODUMP flag */
+#define MADV_USERFAULT 18 /* Trigger user faults if not mapped */
+#define MADV_NOUSERFAULT 19 /* Don't trigger user faults */
+
/* compatibility flags */
#define MAP_FILE 0
diff --git a/arch/mips/include/uapi/asm/mman.h b/arch/mips/include/uapi/asm/mman.h
index cfcb876..d9d11a4 100644
--- a/arch/mips/include/uapi/asm/mman.h
+++ b/arch/mips/include/uapi/asm/mman.h
@@ -84,6 +84,9 @@
overrides the coredump filter bits */
#define MADV_DODUMP 17 /* Clear the MADV_NODUMP flag */
+#define MADV_USERFAULT 18 /* Trigger user faults if not mapped */
+#define MADV_NOUSERFAULT 19 /* Don't trigger user faults */
+
/* compatibility flags */
#define MAP_FILE 0
diff --git a/arch/parisc/include/uapi/asm/mman.h b/arch/parisc/include/uapi/asm/mman.h
index 294d251..7bc7b7b 100644
--- a/arch/parisc/include/uapi/asm/mman.h
+++ b/arch/parisc/include/uapi/asm/mman.h
@@ -66,6 +66,9 @@
overrides the coredump filter bits */
#define MADV_DODUMP 70 /* Clear the MADV_NODUMP flag */
+#define MADV_USERFAULT 71 /* Trigger user faults if not mapped */
+#define MADV_NOUSERFAULT 72 /* Don't trigger user faults */
+
/* compatibility flags */
#define MAP_FILE 0
#define MAP_VARIABLE 0
diff --git a/arch/xtensa/include/uapi/asm/mman.h b/arch/xtensa/include/uapi/asm/mman.h
index 00eed67..5448d88 100644
--- a/arch/xtensa/include/uapi/asm/mman.h
+++ b/arch/xtensa/include/uapi/asm/mman.h
@@ -90,6 +90,9 @@
overrides the coredump filter bits */
#define MADV_DODUMP 17 /* Clear the MADV_NODUMP flag */
+#define MADV_USERFAULT 18 /* Trigger user faults if not mapped */
+#define MADV_NOUSERFAULT 19 /* Don't trigger user faults */
+
/* compatibility flags */
#define MAP_FILE 0
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c05d7cf..f5a410e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -110,6 +110,7 @@ extern unsigned int kobjsize(const void *objp);
#define VM_HUGEPAGE 0x20000000 /* MADV_HUGEPAGE marked this vma */
#define VM_NOHUGEPAGE 0x40000000 /* MADV_NOHUGEPAGE marked this vma */
#define VM_MERGEABLE 0x80000000 /* KSM may merge identical pages */
+#define VM_USERFAULT 0x100000000 /* Trigger user faults if not mapped */
#if defined(CONFIG_X86)
# define VM_PAT VM_ARCH_1 /* PAT reserves whole VMA at once (x86) */
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index ace9a5f..bed1c7c 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -198,7 +198,7 @@ struct page_frag {
#endif
};
-typedef unsigned long __nocast vm_flags_t;
+typedef unsigned long long __nocast vm_flags_t;
/*
* A region containing a mapping of a non-memory backed file under NOMMU
diff --git a/include/uapi/asm-generic/mman-common.h b/include/uapi/asm-generic/mman-common.h
index 4164529..43f36c0 100644
--- a/include/uapi/asm-generic/mman-common.h
+++ b/include/uapi/asm-generic/mman-common.h
@@ -52,6 +52,9 @@
overrides the coredump filter bits */
#define MADV_DODUMP 17 /* Clear the MADV_NODUMP flag */
+#define MADV_USERFAULT 18 /* Trigger user faults if not mapped */
+#define MADV_NOUSERFAULT 19 /* Don't trigger user faults */
+
/* compatibility flags */
#define MAP_FILE 0
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 03a89a2..f46aad1 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -727,6 +727,11 @@ static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
pte_free(mm, pgtable);
} else {
pmd_t entry;
+
+ /* Deliver the page fault to userland */
+ if (vma->vm_flags & VM_USERFAULT)
+ goto do_sigbus;
+
entry = mk_huge_pmd(page, vma);
page_add_new_anon_rmap(page, vma, haddr);
set_pmd_at(mm, haddr, pmd, entry);
@@ -737,6 +742,9 @@ static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
}
return 0;
+do_sigbus:
+ spin_unlock(&mm->page_table_lock);
+ return VM_FAULT_SIGBUS;
}
static inline gfp_t alloc_hugepage_gfpmask(int defrag, gfp_t extra_gfp)
@@ -761,20 +769,17 @@ static inline struct page *alloc_hugepage(int defrag)
}
#endif
-static bool set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
+static void set_huge_zero_page(pgtable_t pgtable, struct mm_struct *mm,
struct vm_area_struct *vma, unsigned long haddr, pmd_t *pmd,
struct page *zero_page)
{
pmd_t entry;
- if (!pmd_none(*pmd))
- return false;
entry = mk_pmd(zero_page, vma->vm_page_prot);
entry = pmd_wrprotect(entry);
entry = pmd_mkhuge(entry);
set_pmd_at(mm, haddr, pmd, entry);
pgtable_trans_huge_deposit(mm, pgtable);
mm->nr_ptes++;
- return true;
}
int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
@@ -794,6 +799,7 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
transparent_hugepage_use_zero_page()) {
pgtable_t pgtable;
struct page *zero_page;
+ int ret;
bool set;
pgtable = pte_alloc_one(mm, haddr);
if (unlikely(!pgtable))
@@ -805,14 +811,24 @@ int do_huge_pmd_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
goto out;
}
spin_lock(&mm->page_table_lock);
- set = set_huge_zero_page(pgtable, mm, vma, haddr, pmd,
- zero_page);
+ ret = 0;
+ set = false;
+ if (pmd_none(*pmd)) {
+ if (vma->vm_flags & VM_USERFAULT)
+ ret = VM_FAULT_SIGBUS;
+ else {
+ set_huge_zero_page(pgtable, mm, vma,
+ haddr, pmd,
+ zero_page);
+ set = true;
+ }
+ }
spin_unlock(&mm->page_table_lock);
if (!set) {
pte_free(mm, pgtable);
put_huge_zero_page();
}
- return 0;
+ return ret;
}
page = alloc_hugepage_vma(transparent_hugepage_defrag(vma),
vma, haddr, numa_node_id(), 0);
@@ -886,16 +902,14 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm,
*/
if (is_huge_zero_pmd(pmd)) {
struct page *zero_page;
- bool set;
/*
* get_huge_zero_page() will never allocate a new page here,
* since we already have a zero page to copy. It just takes a
* reference.
*/
zero_page = get_huge_zero_page();
- set = set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
+ set_huge_zero_page(pgtable, dst_mm, vma, addr, dst_pmd,
zero_page);
- BUG_ON(!set); /* unexpected !pmd_none(dst_pmd) */
ret = 0;
goto out_unlock;
}
diff --git a/mm/madvise.c b/mm/madvise.c
index 7055883..2ecab73 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -93,6 +93,21 @@ static long madvise_behavior(struct vm_area_struct * vma,
if (error)
goto out;
break;
+ case MADV_USERFAULT:
+ if (vma->vm_ops) {
+ error = -EINVAL;
+ goto out;
+ }
+ new_flags |= VM_USERFAULT;
+ break;
+ case MADV_NOUSERFAULT:
+ if (vma->vm_ops) {
+ WARN_ON(new_flags & VM_USERFAULT);
+ error = -EINVAL;
+ goto out;
+ }
+ new_flags &= ~VM_USERFAULT;
+ break;
}
if (new_flags == vma->vm_flags) {
@@ -405,6 +420,7 @@ madvise_behavior_valid(int behavior)
case MADV_HUGEPAGE:
case MADV_NOHUGEPAGE:
#endif
+ case MADV_USERFAULT:
case MADV_DONTDUMP:
case MADV_DODUMP:
return 1;
diff --git a/mm/memory.c b/mm/memory.c
index f7a1fba..044a57c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3235,6 +3235,9 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
page_table = pte_offset_map_lock(mm, pmd, address, &ptl);
if (!pte_none(*page_table))
goto unlock;
+ /* Deliver the page fault to userland, check inside PT lock */
+ if (vma->vm_flags & VM_USERFAULT)
+ goto sigbus;
goto setpte;
}
@@ -3262,6 +3265,10 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
if (!pte_none(*page_table))
goto release;
+ /* Deliver the page fault to userland, check inside PT lock */
+ if (vma->vm_flags & VM_USERFAULT)
+ goto sigbus;
+
inc_mm_counter_fast(mm, MM_ANONPAGES);
page_add_new_anon_rmap(page, vma, address);
setpte:
@@ -3280,6 +3287,9 @@ oom_free_page:
page_cache_release(page);
oom:
return VM_FAULT_OOM;
+sigbus:
+ pte_unmap_unlock(page_table, ptl);
+ return VM_FAULT_SIGBUS;
}
/*
--
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