kernel: Add hooks for user-accessible timers in the kernel.

Hooks for user-accessible timers allow implementation of a more efficient gettimeofday in user-space. Change-Id: If2f63d010c1cf142eb84f3745617e756913e46f7 Signed-off-by: Brent DeGraaf <[email protected]>
cm12-amami · Nov 15, 2012 · 79faa17 · 79faa17
1 parent 5d9616e
commit 79faa17
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Showing 4 changed files with 56 additions and 2 deletions.
diff --git a/include/linux/mm.h b/include/linux/mm.h
@@ -1561,6 +1561,32 @@ int in_gate_area_no_mm(unsigned long addr);
 #define in_gate_area(mm, addr) ({(void)mm; in_gate_area_no_mm(addr);})
 #endif	/* __HAVE_ARCH_GATE_AREA */
 
+#ifdef CONFIG_USE_USER_ACCESSIBLE_TIMERS
+static inline int use_user_accessible_timers(void) { return 1; }
+extern int in_user_timers_area(struct mm_struct *mm, unsigned long addr);
+extern struct vm_area_struct *get_user_timers_vma(struct mm_struct *mm);
+extern int get_user_timer_page(struct vm_area_struct *vma,
+	struct mm_struct *mm, unsigned long start, unsigned int gup_flags,
+	struct page **pages, int idx, int *goto_next_page);
+#else
+static inline int use_user_accessible_timers(void) { return 0; }
+static inline int in_user_timers_area(struct mm_struct *mm, unsigned long addr)
+{
+	return 0;
+}
+static inline struct vm_area_struct *get_user_timers_vma(struct mm_struct *mm)
+{
+	return NULL;
+}
+static inline int get_user_timer_page(struct vm_area_struct *vma,
+	struct mm_struct *mm, unsigned long start, unsigned int gup_flags,
+	struct page **pages, int idx, int *goto_next_page)
+{
+	*goto_next_page = 0;
+	return 0;
+}
+#endif
+
 int drop_caches_sysctl_handler(struct ctl_table *, int,
 					void __user *, size_t *, loff_t *);
 unsigned long shrink_slab(struct shrink_control *shrink,

diff --git a/mm/Kconfig b/mm/Kconfig
@@ -390,3 +390,14 @@ config MEMORY_HOLE_CARVEOUT
           the memory corresponding to the hole to be removed using memblock-
           remove.
 
+config USE_USER_ACCESSIBLE_TIMERS
+	bool "Enables timers accessible from userspace"
+	depends on MMU
+	help
+	  User-accessible timers allow the kernel to map kernel timer
+	  registers to a userspace accessible page, to allow faster
+	  access to time information.  This flag will enable the
+	  interface code in the main kernel.  However, there are
+	  architecture-specific code that will need to be enabled
+	  separately.
+
diff --git a/mm/memory.c b/mm/memory.c
@@ -1726,6 +1726,19 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 			goto next_page;
 		}
 
+		if (use_user_accessible_timers()) {
+			if (!vma && in_user_timers_area(mm, start)) {
+				int goto_next_page = 0;
+				int user_timer_ret = get_user_timer_page(vma,
+					mm, start, gup_flags, pages, i,
+					&goto_next_page);
+				if (goto_next_page)
+					goto next_page;
+				else
+					return user_timer_ret;
+			}
+		}
+
 		if (!vma ||
 		    (vma->vm_flags & (VM_IO | VM_PFNMAP)) ||
 		    !(vm_flags & vma->vm_flags))

diff --git a/mm/mlock.c b/mm/mlock.c
@@ -229,7 +229,9 @@ long mlock_vma_pages_range(struct vm_area_struct *vma,
 
 	if (!((vma->vm_flags & (VM_DONTEXPAND | VM_RESERVED)) ||
 			is_vm_hugetlb_page(vma) ||
-			vma == get_gate_vma(current->mm))) {
+			vma == get_gate_vma(current->mm) ||
+			((use_user_accessible_timers() &&
+				(vma == get_user_timers_vma(current->mm)))))) {
 
 		__mlock_vma_pages_range(vma, start, end, NULL);
 
@@ -324,7 +326,9 @@ static int mlock_fixup(struct vm_area_struct *vma, struct vm_area_struct **prev,
 	int lock = !!(newflags & VM_LOCKED);
 
 	if (newflags == vma->vm_flags || (vma->vm_flags & VM_SPECIAL) ||
-	    is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm))
+	    is_vm_hugetlb_page(vma) || vma == get_gate_vma(current->mm) ||
+	    ((use_user_accessible_timers()) &&
+		(vma == get_user_timers_vma(current->mm))))
 		goto out;	/* don't set VM_LOCKED,  don't count */
 
 	pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);