On Thu, Nov 03, 2016 at 04:01:12PM +0800, Hillf Danton wrote:
> On Thursday, November 03, 2016 3:34 AM Andrea Arcangeli wrote:
> > +void madvise_userfault_dontneed(struct vm_area_struct *vma,
> > + struct vm_area_struct **prev,
> > + unsigned long start, unsigned long end)
> > +{
> > + struct userfaultfd_ctx *ctx;
> > + struct userfaultfd_wait_queue ewq;
> > +
> > + ctx = vma->vm_userfaultfd_ctx.ctx;
> > + if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_MADVDONTNEED))
> > + return;
> > +
> > + userfaultfd_ctx_get(ctx);
> > + *prev = NULL; /* We wait for ACK w/o the mmap semaphore */
> > + up_read(&vma->vm_mm->mmap_sem);
> > +
> > + msg_init(&ewq.msg);
> > +
> > + ewq.msg.event = UFFD_EVENT_MADVDONTNEED;
> > + ewq.msg.arg.madv_dn.start = start;
> > + ewq.msg.arg.madv_dn.end = end;
> > +
> > + userfaultfd_event_wait_completion(ctx, &ewq);
> > +
> > + down_read(&vma->vm_mm->mmap_sem);
>
> After napping with mmap_sem released, is vma still valid?
>
> > +}
> > +
Below is the updated patch that accesses mmap_sem via local reference to
mm_struct rather than via vma.
>From 10b1c5df9db58e863f11be7ebc23e1a3274ccec2 Mon Sep 17 00:00:00 2001
From: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Date: Sun, 20 Mar 2016 14:42:21 +0200
Subject: [PATCH v2] userfaultfd: non-cooperative: Add madvise() event for
MADV_DONTNEED request
If the page is punched out of the address space the uffd reader
should know this and zeromap the respective area in case of
the #PF event.
Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
---
fs/userfaultfd.c | 27 +++++++++++++++++++++++++++
include/linux/userfaultfd_k.h | 12 ++++++++++++
include/uapi/linux/userfaultfd.h | 10 +++++++++-
mm/madvise.c | 2 ++
4 files changed, 50 insertions(+), 1 deletion(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 84fcb05..880e1de 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -598,6 +598,33 @@ void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *vm_ctx,
userfaultfd_event_wait_completion(ctx, &ewq);
}
+void madvise_userfault_dontneed(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start, unsigned long end)
+{
+ struct mm_struct *mm = vma->vm_mm;
+ struct userfaultfd_ctx *ctx;
+ struct userfaultfd_wait_queue ewq;
+
+ ctx = vma->vm_userfaultfd_ctx.ctx;
+ if (!ctx || !(ctx->features & UFFD_FEATURE_EVENT_MADVDONTNEED))
+ return;
+
+ userfaultfd_ctx_get(ctx);
+ *prev = NULL; /* We wait for ACK w/o the mmap semaphore */
+ up_read(&mm->mmap_sem);
+
+ msg_init(&ewq.msg);
+
+ ewq.msg.event = UFFD_EVENT_MADVDONTNEED;
+ ewq.msg.arg.madv_dn.start = start;
+ ewq.msg.arg.madv_dn.end = end;
+
+ userfaultfd_event_wait_completion(ctx, &ewq);
+
+ down_read(&mm->mmap_sem);
+}
+
static int userfaultfd_release(struct inode *inode, struct file *file)
{
struct userfaultfd_ctx *ctx = file->private_data;
diff --git a/include/linux/userfaultfd_k.h b/include/linux/userfaultfd_k.h
index b1cadce..e8a594a 100644
--- a/include/linux/userfaultfd_k.h
+++ b/include/linux/userfaultfd_k.h
@@ -61,6 +61,11 @@ extern void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx *ctx,
unsigned long from, unsigned long to,
unsigned long len);
+extern void madvise_userfault_dontneed(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start,
+ unsigned long end);
+
#else /* CONFIG_USERFAULTFD */
/* mm helpers */
@@ -106,6 +111,13 @@ static inline void mremap_userfaultfd_complete(struct vm_userfaultfd_ctx ctx,
unsigned long len)
{
}
+
+static inline void madvise_userfault_dontneed(struct vm_area_struct *vma,
+ struct vm_area_struct **prev,
+ unsigned long start,
+ unsigned long end)
+{
+}
#endif /* CONFIG_USERFAULTFD */
#endif /* _LINUX_USERFAULTFD_K_H */
diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index 79a85e5..2bbf323 100644
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -19,7 +19,8 @@
*/
#define UFFD_API ((__u64)0xAA)
#define UFFD_API_FEATURES (UFFD_FEATURE_EVENT_FORK | \
- UFFD_FEATURE_EVENT_REMAP)
+ UFFD_FEATURE_EVENT_REMAP | \
+ UFFD_FEATURE_EVENT_MADVDONTNEED)
#define UFFD_API_IOCTLS \
((__u64)1 << _UFFDIO_REGISTER | \
(__u64)1 << _UFFDIO_UNREGISTER | \
@@ -84,6 +85,11 @@ struct uffd_msg {
} remap;
struct {
+ __u64 start;
+ __u64 end;
+ } madv_dn;
+
+ struct {
/* unused reserved fields */
__u64 reserved1;
__u64 reserved2;
@@ -98,6 +104,7 @@ struct uffd_msg {
#define UFFD_EVENT_PAGEFAULT 0x12
#define UFFD_EVENT_FORK 0x13
#define UFFD_EVENT_REMAP 0x14
+#define UFFD_EVENT_MADVDONTNEED 0x15
/* flags for UFFD_EVENT_PAGEFAULT */
#define UFFD_PAGEFAULT_FLAG_WRITE (1<<0) /* If this was a write fault */
@@ -119,6 +126,7 @@ struct uffdio_api {
#define UFFD_FEATURE_PAGEFAULT_FLAG_WP (1<<0)
#define UFFD_FEATURE_EVENT_FORK (1<<1)
#define UFFD_FEATURE_EVENT_REMAP (1<<2)
+#define UFFD_FEATURE_EVENT_MADVDONTNEED (1<<3)
__u64 features;
__u64 ioctls;
diff --git a/mm/madvise.c b/mm/madvise.c
index 93fb63e..7168bc6 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -10,6 +10,7 @@
#include <linux/syscalls.h>
#include <linux/mempolicy.h>
#include <linux/page-isolation.h>
+#include <linux/userfaultfd_k.h>
#include <linux/hugetlb.h>
#include <linux/falloc.h>
#include <linux/sched.h>
@@ -476,6 +477,7 @@ static long madvise_dontneed(struct vm_area_struct *vma,
return -EINVAL;
zap_page_range(vma, start, end - start, NULL);
+ madvise_userfault_dontneed(vma, prev, start, end);
return 0;
}
--
1.9.1
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