[PATCH v2 0/2] mm: unexport __get_user_pages_unlocked()

[PATCH v2 0/2] mm: unexport __get_user_pages_unlocked()

[Lorenzo Stoakes]

This patch series continues the cleanup of get_user_pages*() functions taking
advantage of the fact we can now pass gup_flags as we please.

It firstly adds an additional 'locked' parameter to get_user_pages_remote() to
allow for its callers to utilise VM_FAULT_RETRY functionality. This is necessary
as the invocation of __get_user_pages_unlocked() in process_vm_rw_single_vec()
makes use of this and no other existing higher level function would allow it to
do so.

Secondly existing callers of __get_user_pages_unlocked() are replaced with the
appropriate higher-level replacement - get_user_pages_unlocked() if the current
task and memory descriptor are referenced, or get_user_pages_remote() if other
task/memory descriptors are referenced (having acquiring mmap_sem.)

Lorenzo Stoakes (2):
  mm: add locked parameter to get_user_pages_remote()
  mm: unexport __get_user_pages_unlocked()

 drivers/gpu/drm/etnaviv/etnaviv_gem.c   |  2 +-
 drivers/gpu/drm/i915/i915_gem_userptr.c |  2 +-
 drivers/infiniband/core/umem_odp.c      |  2 +-
 fs/exec.c                               |  2 +-
 include/linux/mm.h                      |  5 +----
 kernel/events/uprobes.c                 |  4 ++--
 mm/gup.c                                | 20 ++++++++++++--------
 mm/memory.c                             |  2 +-
 mm/nommu.c                              |  7 +++----
 mm/process_vm_access.c                  | 12 ++++++++----
 security/tomoyo/domain.c                |  2 +-
 virt/kvm/async_pf.c                     | 10 +++++++---
 virt/kvm/kvm_main.c                     |  5 ++---
 13 files changed, 41 insertions(+), 34 deletions(-)

[PATCH v2 1/2] mm: add locked parameter to get_user_pages_remote()

[Lorenzo Stoakes]

This patch adds an int *locked parameter to get_user_pages_remote() to allow
VM_FAULT_RETRY faulting behaviour similar to get_user_pages_[un]locked().

It additionally clears the way for __get_user_pages_unlocked() to be unexported
as its sole remaining useful characteristic was to allow for VM_FAULT_RETRY
behaviour when faulting in pages.

It should not introduce any functional changes, however it does allow for
subsequent changes to get_user_pages_remote() callers to take advantage of
VM_FAULT_RETRY.

Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
---
v2: updated description

 drivers/gpu/drm/etnaviv/etnaviv_gem.c   |  2 +-
 drivers/gpu/drm/i915/i915_gem_userptr.c |  2 +-
 drivers/infiniband/core/umem_odp.c      |  2 +-
 fs/exec.c                               |  2 +-
 include/linux/mm.h                      |  2 +-
 kernel/events/uprobes.c                 |  4 ++--
 mm/gup.c                                | 12 ++++++++----
 mm/memory.c                             |  2 +-
 security/tomoyo/domain.c                |  2 +-
 9 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
index 0370b84..0c69a97f 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
@@ -763,7 +763,7 @@ static struct page **etnaviv_gem_userptr_do_get_pages(
 	down_read(&mm->mmap_sem);
 	while (pinned < npages) {
 		ret = get_user_pages_remote(task, mm, ptr, npages - pinned,
-					    flags, pvec + pinned, NULL);
+					    flags, pvec + pinned, NULL, NULL);
 		if (ret < 0)
 			break;

diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index c6f780f..836b525 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -522,7 +522,7 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
 					 obj->userptr.ptr + pinned * PAGE_SIZE,
 					 npages - pinned,
 					 flags,
-					 pvec + pinned, NULL);
+					 pvec + pinned, NULL, NULL);
 				if (ret < 0)
 					break;

diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c
index 1f0fe32..6b079a3 100644
--- a/drivers/infiniband/core/umem_odp.c
+++ b/drivers/infiniband/core/umem_odp.c
@@ -578,7 +578,7 @@ int ib_umem_odp_map_dma_pages(struct ib_umem *umem, u64 user_virt, u64 bcnt,
 		 */
 		npages = get_user_pages_remote(owning_process, owning_mm,
 				user_virt, gup_num_pages,
-				flags, local_page_list, NULL);
+				flags, local_page_list, NULL, NULL);
 		up_read(&owning_mm->mmap_sem);

 		if (npages < 0)
diff --git a/fs/exec.c b/fs/exec.c
index 4e497b9..2cf049d 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -209,7 +209,7 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
 	 * doing the exec and bprm->mm is the new process's mm.
 	 */
 	ret = get_user_pages_remote(current, bprm->mm, pos, 1, gup_flags,
-			&page, NULL);
+			&page, NULL, NULL);
 	if (ret <= 0)
 		return NULL;

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a92c8d7..cc15445 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1274,7 +1274,7 @@ extern int access_remote_vm(struct mm_struct *mm, unsigned long addr,
 long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
 			    unsigned long start, unsigned long nr_pages,
 			    unsigned int gup_flags, struct page **pages,
-			    struct vm_area_struct **vmas);
+			    struct vm_area_struct **vmas, int *locked);
 long get_user_pages(unsigned long start, unsigned long nr_pages,
 			    unsigned int gup_flags, struct page **pages,
 			    struct vm_area_struct **vmas);
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index f9ec9ad..215871b 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -301,7 +301,7 @@ int uprobe_write_opcode(struct mm_struct *mm, unsigned long vaddr,
 retry:
 	/* Read the page with vaddr into memory */
 	ret = get_user_pages_remote(NULL, mm, vaddr, 1, FOLL_FORCE, &old_page,
-			&vma);
+			&vma, NULL);
 	if (ret <= 0)
 		return ret;

@@ -1712,7 +1712,7 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr)
 	 * essentially a kernel access to the memory.
 	 */
 	result = get_user_pages_remote(NULL, mm, vaddr, 1, FOLL_FORCE, &page,
-			NULL);
+			NULL, NULL);
 	if (result < 0)
 		return result;

diff --git a/mm/gup.c b/mm/gup.c
index ec4f827..0567851 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -920,6 +920,9 @@ EXPORT_SYMBOL(get_user_pages_unlocked);
  *		only intends to ensure the pages are faulted in.
  * @vmas:	array of pointers to vmas corresponding to each page.
  *		Or NULL if the caller does not require them.
+ * @locked:	pointer to lock flag indicating whether lock is held and
+ *		subsequently whether VM_FAULT_RETRY functionality can be
+ *		utilised. Lock must initially be held.
  *
  * Returns number of pages pinned. This may be fewer than the number
  * requested. If nr_pages is 0 or negative, returns 0. If no pages
@@ -963,10 +966,10 @@ EXPORT_SYMBOL(get_user_pages_unlocked);
 long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
 		unsigned long start, unsigned long nr_pages,
 		unsigned int gup_flags, struct page **pages,
-		struct vm_area_struct **vmas)
+		struct vm_area_struct **vmas, int *locked)
 {
 	return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
-				       NULL, false,
+				       locked, true,
 				       gup_flags | FOLL_TOUCH | FOLL_REMOTE);
 }
 EXPORT_SYMBOL(get_user_pages_remote);
@@ -974,8 +977,9 @@ EXPORT_SYMBOL(get_user_pages_remote);
 /*
  * This is the same as get_user_pages_remote(), just with a
  * less-flexible calling convention where we assume that the task
- * and mm being operated on are the current task's.  We also
- * obviously don't pass FOLL_REMOTE in here.
+ * and mm being operated on are the current task's and don't allow
+ * passing of a locked parameter.  We also obviously don't pass
+ * FOLL_REMOTE in here.
  */
 long get_user_pages(unsigned long start, unsigned long nr_pages,
 		unsigned int gup_flags, struct page **pages,
diff --git a/mm/memory.c b/mm/memory.c
index e18c57b..2f3949b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3883,7 +3883,7 @@ static int __access_remote_vm(struct task_struct *tsk, struct mm_struct *mm,
 		struct page *page = NULL;

 		ret = get_user_pages_remote(tsk, mm, addr, 1,
-				gup_flags, &page, &vma);
+				gup_flags, &page, &vma, NULL);
 		if (ret <= 0) {
 #ifndef CONFIG_HAVE_IOREMAP_PROT
 			break;
diff --git a/security/tomoyo/domain.c b/security/tomoyo/domain.c
index 682b73a..838ffa7 100644
--- a/security/tomoyo/domain.c
+++ b/security/tomoyo/domain.c
@@ -881,7 +881,7 @@ bool tomoyo_dump_page(struct linux_binprm *bprm, unsigned long pos,
 	 * the execve().
 	 */
 	if (get_user_pages_remote(current, bprm->mm, pos, 1,
-				FOLL_FORCE, &page, NULL) <= 0)
+				FOLL_FORCE, &page, NULL, NULL) <= 0)
 		return false;
 #else
 	page = bprm->page[pos / PAGE_SIZE];
--
2.10.1

[PATCH v2 2/2] mm: unexport __get_user_pages_unlocked()

[Lorenzo Stoakes]

This patch unexports the low-level __get_user_pages_unlocked() function and
replaces invocations with calls to more appropriate higher-level functions.

In hva_to_pfn_slow() we are able to replace __get_user_pages_unlocked() with
get_user_pages_unlocked() since we can now pass gup_flags.

In async_pf_execute() and process_vm_rw_single_vec() we need to pass different
tsk, mm arguments so get_user_pages_remote() is the sane replacement in these
cases (having added manual acquisition and release of mmap_sem.)

Additionally get_user_pages_remote() reintroduces use of the FOLL_TOUCH
flag. However, this flag was originally silently dropped by 1e9877902dc7e
("mm/gup: Introduce get_user_pages_remote()"), so this appears to have been
unintentional and reintroducing it is therefore not an issue.

Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
---
v2: updated patch to apply against mainline rather than -mmots

 include/linux/mm.h     |  3 ---
 mm/gup.c               |  8 ++++----
 mm/nommu.c             |  7 +++----
 mm/process_vm_access.c | 12 ++++++++----
 virt/kvm/async_pf.c    | 10 +++++++---
 virt/kvm/kvm_main.c    |  5 ++---
 6 files changed, 24 insertions(+), 21 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index cc15445..7b2d14e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1280,9 +1280,6 @@ long get_user_pages(unsigned long start, unsigned long nr_pages,
 			    struct vm_area_struct **vmas);
 long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
 		    unsigned int gup_flags, struct page **pages, int *locked);
-long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
-			       unsigned long start, unsigned long nr_pages,
-			       struct page **pages, unsigned int gup_flags);
 long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
 		    struct page **pages, unsigned int gup_flags);
 int get_user_pages_fast(unsigned long start, int nr_pages, int write,
diff --git a/mm/gup.c b/mm/gup.c
index 0567851..8028af1 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -866,9 +866,10 @@ EXPORT_SYMBOL(get_user_pages_locked);
  * according to the parameters "pages", "write", "force"
  * respectively.
  */
-__always_inline long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
-					       unsigned long start, unsigned long nr_pages,
-					       struct page **pages, unsigned int gup_flags)
+static __always_inline long __get_user_pages_unlocked(struct task_struct *tsk,
+		struct mm_struct *mm, unsigned long start,
+		unsigned long nr_pages, struct page **pages,
+		unsigned int gup_flags)
 {
 	long ret;
 	int locked = 1;
@@ -880,7 +881,6 @@ __always_inline long __get_user_pages_unlocked(struct task_struct *tsk, struct m
 		up_read(&mm->mmap_sem);
 	return ret;
 }
-EXPORT_SYMBOL(__get_user_pages_unlocked);

 /*
  * get_user_pages_unlocked() is suitable to replace the form:
diff --git a/mm/nommu.c b/mm/nommu.c
index 8b8faaf..669437b 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -176,9 +176,9 @@ long get_user_pages_locked(unsigned long start, unsigned long nr_pages,
 }
 EXPORT_SYMBOL(get_user_pages_locked);

-long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
-			       unsigned long start, unsigned long nr_pages,
-			       struct page **pages, unsigned int gup_flags)
+static long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
+				      unsigned long start, unsigned long nr_pages,
+			              struct page **pages, unsigned int gup_flags)
 {
 	long ret;
 	down_read(&mm->mmap_sem);
@@ -187,7 +187,6 @@ long __get_user_pages_unlocked(struct task_struct *tsk, struct mm_struct *mm,
 	up_read(&mm->mmap_sem);
 	return ret;
 }
-EXPORT_SYMBOL(__get_user_pages_unlocked);

 long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
 			     struct page **pages, unsigned int gup_flags)
diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
index be8dc8d..84d0c7e 100644
--- a/mm/process_vm_access.c
+++ b/mm/process_vm_access.c
@@ -88,7 +88,7 @@ static int process_vm_rw_single_vec(unsigned long addr,
 	ssize_t rc = 0;
 	unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
 		/ sizeof(struct pages *);
-	unsigned int flags = FOLL_REMOTE;
+	unsigned int flags = 0;

 	/* Work out address and page range required */
 	if (len == 0)
@@ -100,15 +100,19 @@ static int process_vm_rw_single_vec(unsigned long addr,

 	while (!rc && nr_pages && iov_iter_count(iter)) {
 		int pages = min(nr_pages, max_pages_per_loop);
+		int locked = 1;
 		size_t bytes;

 		/*
 		 * Get the pages we're interested in.  We must
-		 * add FOLL_REMOTE because task/mm might not
+		 * access remotely because task/mm might not
 		 * current/current->mm
 		 */
-		pages = __get_user_pages_unlocked(task, mm, pa, pages,
-						  process_pages, flags);
+		down_read(&mm->mmap_sem);
+		pages = get_user_pages_remote(task, mm, pa, pages, flags,
+					      process_pages, NULL, &locked);
+		if (locked)
+			up_read(&mm->mmap_sem);
 		if (pages <= 0)
 			return -EFAULT;

diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 8035cc1..dab8b19 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -76,16 +76,20 @@ static void async_pf_execute(struct work_struct *work)
 	struct kvm_vcpu *vcpu = apf->vcpu;
 	unsigned long addr = apf->addr;
 	gva_t gva = apf->gva;
+	int locked = 1;

 	might_sleep();

 	/*
 	 * This work is run asynchromously to the task which owns
 	 * mm and might be done in another context, so we must
-	 * use FOLL_REMOTE.
+	 * access remotely.
 	 */
-	__get_user_pages_unlocked(NULL, mm, addr, 1, NULL,
-			FOLL_WRITE | FOLL_REMOTE);
+	down_read(&mm->mmap_sem);
+	get_user_pages_remote(NULL, mm, addr, 1, FOLL_WRITE, NULL, NULL,
+			&locked);
+	if (locked)
+		up_read(&mm->mmap_sem);

 	kvm_async_page_present_sync(vcpu, apf);

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2907b7b..c45d951 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1415,13 +1415,12 @@ static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
 		npages = get_user_page_nowait(addr, write_fault, page);
 		up_read(&current->mm->mmap_sem);
 	} else {
-		unsigned int flags = FOLL_TOUCH | FOLL_HWPOISON;
+		unsigned int flags = FOLL_HWPOISON;

 		if (write_fault)
 			flags |= FOLL_WRITE;

-		npages = __get_user_pages_unlocked(current, current->mm, addr, 1,
-						   page, flags);
+		npages = get_user_pages_unlocked(addr, 1, page, flags);
 	}
 	if (npages != 1)
 		return npages;
--
2.10.1