Merge branch 'sparc-perf-events-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'sparc-perf-events-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  mm, perf_event: Make vmalloc_user() align base kernel virtual address to SHMLBA
  perf_event: Provide vmalloc() based mmap() backing

6 files changed, 240 insertions, 84 deletions

diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index ac45aab741a5..05ef5380a687 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -26,6 +26,7 @@ config SPARC
         select RTC_CLASS
         select RTC_DRV_M48T59
         select HAVE_PERF_EVENTS
+        select PERF_USE_VMALLOC
         select HAVE_DMA_ATTRS
         select HAVE_DMA_API_DEBUG
 
@@ -48,6 +49,7 @@ config SPARC64
         select RTC_DRV_SUN4V
         select RTC_DRV_STARFIRE
         select HAVE_PERF_EVENTS
+        select PERF_USE_VMALLOC
 
 config ARCH_DEFCONFIG
         string
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 3a9d36d1e92a..2e6d95f97419 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -442,6 +442,7 @@ enum perf_callchain_context {
 #include <linux/hrtimer.h>
 #include <linux/fs.h>
 #include <linux/pid_namespace.h>
+#include <linux/workqueue.h>
 #include <asm/atomic.h>
 
 #define PERF_MAX_STACK_DEPTH            255
@@ -513,6 +514,10 @@ struct file;
 
 struct perf_mmap_data {
         struct rcu_head                 rcu_head;
+#ifdef CONFIG_PERF_USE_VMALLOC
+        struct work_struct              work;
+#endif
+        int                             data_order;
         int                             nr_pages;       /* nr of data pages  */
         int                             writable;       /* are we writable   */
         int                             nr_locked;      /* nr pages mlocked  */
diff --git a/init/Kconfig b/init/Kconfig
index c7bac39d6c61..09c5c6431f42 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -921,6 +921,11 @@ config HAVE_PERF_EVENTS
         help
           See tools/perf/design.txt for details.
 
+config PERF_USE_VMALLOC
+        bool
+        help
+          See tools/perf/design.txt for details
+
 menu "Kernel Performance Events And Counters"
 
 config PERF_EVENTS
@@ -976,6 +981,19 @@ config PERF_COUNTERS
 
           Say N if unsure.
 
+config DEBUG_PERF_USE_VMALLOC
+        default n
+        bool "Debug: use vmalloc to back perf mmap() buffers"
+        depends on PERF_EVENTS && DEBUG_KERNEL
+        select PERF_USE_VMALLOC
+        help
+         Use vmalloc memory to back perf mmap() buffers.
+
+         Mostly useful for debugging the vmalloc code on platforms
+         that don't require it.
+
+         Say N if unsure.
+
 endmenu
 
 config VM_EVENT_COUNTERS
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index e491fb087939..9d0b5c665883 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -20,6 +20,7 @@
 #include <linux/percpu.h>
 #include <linux/ptrace.h>
 #include <linux/vmstat.h>
+#include <linux/vmalloc.h>
 #include <linux/hardirq.h>
 #include <linux/rculist.h>
 #include <linux/uaccess.h>
@@ -2091,49 +2092,31 @@ unlock:
         rcu_read_unlock();
 }
 
-static int perf_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+static unsigned long perf_data_size(struct perf_mmap_data *data)
 {
-        struct perf_event *event = vma->vm_file->private_data;
-        struct perf_mmap_data *data;
-        int ret = VM_FAULT_SIGBUS;
-
-        if (vmf->flags & FAULT_FLAG_MKWRITE) {
-                if (vmf->pgoff == 0)
-                        ret = 0;
-                return ret;
-        }
-
-        rcu_read_lock();
-        data = rcu_dereference(event->data);
-        if (!data)
-                goto unlock;
-
-        if (vmf->pgoff == 0) {
-                vmf->page = virt_to_page(data->user_page);
-        } else {
-                int nr = vmf->pgoff - 1;
-
-                if ((unsigned)nr > data->nr_pages)
-                        goto unlock;
+        return data->nr_pages << (PAGE_SHIFT + data->data_order);
+}
 
-                if (vmf->flags & FAULT_FLAG_WRITE)
-                        goto unlock;
+#ifndef CONFIG_PERF_USE_VMALLOC
 
-                vmf->page = virt_to_page(data->data_pages[nr]);
-        }
+/*
+ * Back perf_mmap() with regular GFP_KERNEL-0 pages.
+ */
 
-        get_page(vmf->page);
-        vmf->page->mapping = vma->vm_file->f_mapping;
-        vmf->page->index   = vmf->pgoff;
+static struct page *
+perf_mmap_to_page(struct perf_mmap_data *data, unsigned long pgoff)
+{
+        if (pgoff > data->nr_pages)
+                return NULL;
 
-        ret = 0;
-unlock:
-        rcu_read_unlock();
+        if (pgoff == 0)
+                return virt_to_page(data->user_page);
 
-        return ret;
+        return virt_to_page(data->data_pages[pgoff - 1]);
 }
 
-static int perf_mmap_data_alloc(struct perf_event *event, int nr_pages)
+static struct perf_mmap_data *
+perf_mmap_data_alloc(struct perf_event *event, int nr_pages)
 {
         struct perf_mmap_data *data;
         unsigned long size;
@@ -2158,19 +2141,10 @@ static int perf_mmap_data_alloc(struct perf_event *event, int nr_pages)
                         goto fail_data_pages;
         }
 
+        data->data_order = 0;
         data->nr_pages = nr_pages;
-        atomic_set(&data->lock, -1);
-
-        if (event->attr.watermark) {
-                data->watermark = min_t(long, PAGE_SIZE * nr_pages,
-                                      event->attr.wakeup_watermark);
-        }
-        if (!data->watermark)
-                data->watermark = max(PAGE_SIZE, PAGE_SIZE * nr_pages / 4);
 
-        rcu_assign_pointer(event->data, data);
-
-        return 0;
+        return data;
 
 fail_data_pages:
         for (i--; i >= 0; i--)
@@ -2182,7 +2156,7 @@ fail_user_page:
         kfree(data);
 
 fail:
-        return -ENOMEM;
+        return NULL;
 }
 
 static void perf_mmap_free_page(unsigned long addr)
@@ -2193,28 +2167,169 @@ static void perf_mmap_free_page(unsigned long addr)
         __free_page(page);
 }
 
-static void __perf_mmap_data_free(struct rcu_head *rcu_head)
+static void perf_mmap_data_free(struct perf_mmap_data *data)
 {
-        struct perf_mmap_data *data;
         int i;
 
-        data = container_of(rcu_head, struct perf_mmap_data, rcu_head);
-
         perf_mmap_free_page((unsigned long)data->user_page);
         for (i = 0; i < data->nr_pages; i++)
                 perf_mmap_free_page((unsigned long)data->data_pages[i]);
+}
+
+#else
+
+/*
+ * Back perf_mmap() with vmalloc memory.
+ *
+ * Required for architectures that have d-cache aliasing issues.
+ */
+
+static struct page *
+perf_mmap_to_page(struct perf_mmap_data *data, unsigned long pgoff)
+{
+        if (pgoff > (1UL << data->data_order))
+                return NULL;
+
+        return vmalloc_to_page((void *)data->user_page + pgoff * PAGE_SIZE);
+}
+
+static void perf_mmap_unmark_page(void *addr)
+{
+        struct page *page = vmalloc_to_page(addr);
+
+        page->mapping = NULL;
+}
+
+static void perf_mmap_data_free_work(struct work_struct *work)
+{
+        struct perf_mmap_data *data;
+        void *base;
+        int i, nr;
+
+        data = container_of(work, struct perf_mmap_data, work);
+        nr = 1 << data->data_order;
+
+        base = data->user_page;
+        for (i = 0; i < nr + 1; i++)
+                perf_mmap_unmark_page(base + (i * PAGE_SIZE));
+
+        vfree(base);
+}
+
+static void perf_mmap_data_free(struct perf_mmap_data *data)
+{
+        schedule_work(&data->work);
+}
+
+static struct perf_mmap_data *
+perf_mmap_data_alloc(struct perf_event *event, int nr_pages)
+{
+        struct perf_mmap_data *data;
+        unsigned long size;
+        void *all_buf;
 
+        WARN_ON(atomic_read(&event->mmap_count));
+
+        size = sizeof(struct perf_mmap_data);
+        size += sizeof(void *);
+
+        data = kzalloc(size, GFP_KERNEL);
+        if (!data)
+                goto fail;
+
+        INIT_WORK(&data->work, perf_mmap_data_free_work);
+
+        all_buf = vmalloc_user((nr_pages + 1) * PAGE_SIZE);
+        if (!all_buf)
+                goto fail_all_buf;
+
+        data->user_page = all_buf;
+        data->data_pages[0] = all_buf + PAGE_SIZE;
+        data->data_order = ilog2(nr_pages);
+        data->nr_pages = 1;
+
+        return data;
+
+fail_all_buf:
+        kfree(data);
+
+fail:
+        return NULL;
+}
+
+#endif
+
+static int perf_mmap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+        struct perf_event *event = vma->vm_file->private_data;
+        struct perf_mmap_data *data;
+        int ret = VM_FAULT_SIGBUS;
+
+        if (vmf->flags & FAULT_FLAG_MKWRITE) {
+                if (vmf->pgoff == 0)
+                        ret = 0;
+                return ret;
+        }
+
+        rcu_read_lock();
+        data = rcu_dereference(event->data);
+        if (!data)
+                goto unlock;
+
+        if (vmf->pgoff && (vmf->flags & FAULT_FLAG_WRITE))
+                goto unlock;
+
+        vmf->page = perf_mmap_to_page(data, vmf->pgoff);
+        if (!vmf->page)
+                goto unlock;
+
+        get_page(vmf->page);
+        vmf->page->mapping = vma->vm_file->f_mapping;
+        vmf->page->index   = vmf->pgoff;
+
+        ret = 0;
+unlock:
+        rcu_read_unlock();
+
+        return ret;
+}
+
+static void
+perf_mmap_data_init(struct perf_event *event, struct perf_mmap_data *data)
+{
+        long max_size = perf_data_size(data);
+
+        atomic_set(&data->lock, -1);
+
+        if (event->attr.watermark) {
+                data->watermark = min_t(long, max_size,
+                                        event->attr.wakeup_watermark);
+        }
+
+        if (!data->watermark)
+                data->watermark = max_t(long, PAGE_SIZE, max_size / 2);
+
+
+        rcu_assign_pointer(event->data, data);
+}
+
+static void perf_mmap_data_free_rcu(struct rcu_head *rcu_head)
+{
+        struct perf_mmap_data *data;
+
+        data = container_of(rcu_head, struct perf_mmap_data, rcu_head);
+        perf_mmap_data_free(data);
         kfree(data);
 }
 
-static void perf_mmap_data_free(struct perf_event *event)
+static void perf_mmap_data_release(struct perf_event *event)
 {
         struct perf_mmap_data *data = event->data;
 
         WARN_ON(atomic_read(&event->mmap_count));
 
         rcu_assign_pointer(event->data, NULL);
-        call_rcu(&data->rcu_head, __perf_mmap_data_free);
+        call_rcu(&data->rcu_head, perf_mmap_data_free_rcu);
 }
 
 static void perf_mmap_open(struct vm_area_struct *vma)
@@ -2230,11 +2345,12 @@ static void perf_mmap_close(struct vm_area_struct *vma)
 
         WARN_ON_ONCE(event->ctx->parent_ctx);
         if (atomic_dec_and_mutex_lock(&event->mmap_count, &event->mmap_mutex)) {
+                unsigned long size = perf_data_size(event->data);
                 struct user_struct *user = current_user();
 
-                atomic_long_sub(event->data->nr_pages + 1, &user->locked_vm);
+                atomic_long_sub((size >> PAGE_SHIFT) + 1, &user->locked_vm);
                 vma->vm_mm->locked_vm -= event->data->nr_locked;
-                perf_mmap_data_free(event);
+                perf_mmap_data_release(event);
                 mutex_unlock(&event->mmap_mutex);
         }
 }
@@ -2252,6 +2368,7 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
         unsigned long user_locked, user_lock_limit;
         struct user_struct *user = current_user();
         unsigned long locked, lock_limit;
+        struct perf_mmap_data *data;
         unsigned long vma_size;
         unsigned long nr_pages;
         long user_extra, extra;
@@ -2314,10 +2431,15 @@ static int perf_mmap(struct file *file, struct vm_area_struct *vma)
         }
 
         WARN_ON(event->data);
-        ret = perf_mmap_data_alloc(event, nr_pages);
-        if (ret)
+
+        data = perf_mmap_data_alloc(event, nr_pages);
+        ret = -ENOMEM;
+        if (!data)
                 goto unlock;
 
+        ret = 0;
+        perf_mmap_data_init(event, data);
+
         atomic_set(&event->mmap_count, 1);
         atomic_long_add(user_extra, &user->locked_vm);
         vma->vm_mm->locked_vm += extra;
@@ -2505,7 +2627,7 @@ static bool perf_output_space(struct perf_mmap_data *data, unsigned long tail,
         if (!data->writable)
                 return true;
 
-        mask = (data->nr_pages << PAGE_SHIFT) - 1;
+        mask = perf_data_size(data) - 1;
 
         offset = (offset - tail) & mask;
         head   = (head   - tail) & mask;
@@ -2610,7 +2732,7 @@ void perf_output_copy(struct perf_output_handle *handle,
                       const void *buf, unsigned int len)
 {
         unsigned int pages_mask;
-        unsigned int offset;
+        unsigned long offset;
         unsigned int size;
         void **pages;
 
@@ -2619,12 +2741,14 @@ void perf_output_copy(struct perf_output_handle *handle,
         pages           = handle->data->data_pages;
 
         do {
-                unsigned int page_offset;
+                unsigned long page_offset;
+                unsigned long page_size;
                 int nr;
 
                 nr          = (offset >> PAGE_SHIFT) & pages_mask;
-                page_offset = offset & (PAGE_SIZE - 1);
-                size        = min_t(unsigned int, PAGE_SIZE - page_offset, len);
+                page_size   = 1UL << (handle->data->data_order + PAGE_SHIFT);
+                page_offset = offset & (page_size - 1);
+                size        = min_t(unsigned int, page_size - page_offset, len);
 
                 memcpy(pages[nr] + page_offset, buf, size);
 
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 2f7c9d75c552..5e7aed0802bf 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -28,6 +28,7 @@
 #include <asm/atomic.h>
 #include <asm/uaccess.h>
 #include <asm/tlbflush.h>
+#include <asm/shmparam.h>
 
 
 /*** Page table manipulation functions ***/
@@ -1155,12 +1156,11 @@ static void insert_vmalloc_vm(struct vm_struct *vm, struct vmap_area *va,
 }
 
 static struct vm_struct *__get_vm_area_node(unsigned long size,
-                unsigned long flags, unsigned long start, unsigned long end,
-                int node, gfp_t gfp_mask, void *caller)
+                unsigned long align, unsigned long flags, unsigned long start,
+                unsigned long end, int node, gfp_t gfp_mask, void *caller)
 {
         static struct vmap_area *va;
         struct vm_struct *area;
-        unsigned long align = 1;
 
         BUG_ON(in_interrupt());
         if (flags & VM_IOREMAP) {
@@ -1200,7 +1200,7 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
 struct vm_struct *__get_vm_area(unsigned long size, unsigned long flags,
                                 unsigned long start, unsigned long end)
 {
-        return __get_vm_area_node(size, flags, start, end, -1, GFP_KERNEL,
+        return __get_vm_area_node(size, 1, flags, start, end, -1, GFP_KERNEL,
                                                 __builtin_return_address(0));
 }
 EXPORT_SYMBOL_GPL(__get_vm_area);
@@ -1209,7 +1209,7 @@ struct vm_struct *__get_vm_area_caller(unsigned long size, unsigned long flags,
                                        unsigned long start, unsigned long end,
                                        void *caller)
 {
-        return __get_vm_area_node(size, flags, start, end, -1, GFP_KERNEL,
+        return __get_vm_area_node(size, 1, flags, start, end, -1, GFP_KERNEL,
                                   caller);
 }
 
@@ -1224,22 +1224,22 @@ struct vm_struct *__get_vm_area_caller(unsigned long size, unsigned long flags,
  */
 struct vm_struct *get_vm_area(unsigned long size, unsigned long flags)
 {
-        return __get_vm_area_node(size, flags, VMALLOC_START, VMALLOC_END,
+        return __get_vm_area_node(size, 1, flags, VMALLOC_START, VMALLOC_END,
                                 -1, GFP_KERNEL, __builtin_return_address(0));
 }
 
 struct vm_struct *get_vm_area_caller(unsigned long size, unsigned long flags,
                                 void *caller)
 {
-        return __get_vm_area_node(size, flags, VMALLOC_START, VMALLOC_END,
+        return __get_vm_area_node(size, 1, flags, VMALLOC_START, VMALLOC_END,
                                                 -1, GFP_KERNEL, caller);
 }
 
 struct vm_struct *get_vm_area_node(unsigned long size, unsigned long flags,
                                    int node, gfp_t gfp_mask)
 {
-        return __get_vm_area_node(size, flags, VMALLOC_START, VMALLOC_END, node,
-                                  gfp_mask, __builtin_return_address(0));
+        return __get_vm_area_node(size, 1, flags, VMALLOC_START, VMALLOC_END,
+                                  node, gfp_mask, __builtin_return_address(0));
 }
 
 static struct vm_struct *find_vm_area(const void *addr)
@@ -1402,7 +1402,8 @@ void *vmap(struct page **pages, unsigned int count,
 }
 EXPORT_SYMBOL(vmap);
 
-static void *__vmalloc_node(unsigned long size, gfp_t gfp_mask, pgprot_t prot,
+static void *__vmalloc_node(unsigned long size, unsigned long align,
+                            gfp_t gfp_mask, pgprot_t prot,
                             int node, void *caller);
 static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
                                  pgprot_t prot, int node, void *caller)
@@ -1416,7 +1417,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask,
         area->nr_pages = nr_pages;
         /* Please note that the recursion is strictly bounded. */
         if (array_size > PAGE_SIZE) {
-                pages = __vmalloc_node(array_size, gfp_mask | __GFP_ZERO,
+                pages = __vmalloc_node(array_size, 1, gfp_mask | __GFP_ZERO,
                                 PAGE_KERNEL, node, caller);
                 area->flags |= VM_VPAGES;
         } else {
@@ -1475,6 +1476,7 @@ void *__vmalloc_area(struct vm_struct *area, gfp_t gfp_mask, pgprot_t prot)
 /**
  *      __vmalloc_node  -  allocate virtually contiguous memory
  *      @size:          allocation size
+ *      @align:         desired alignment
  *      @gfp_mask:      flags for the page level allocator
  *      @prot:          protection mask for the allocated pages
  *      @node:          node to use for allocation or -1
@@ -1484,8 +1486,9 @@ void *__vmalloc_area(struct vm_struct *area, gfp_t gfp_mask, pgprot_t prot)
  *      allocator with @gfp_mask flags.  Map them into contiguous
  *      kernel virtual space, using a pagetable protection of @prot.
  */
-static void *__vmalloc_node(unsigned long size, gfp_t gfp_mask, pgprot_t prot,
-                                                int node, void *caller)
+static void *__vmalloc_node(unsigned long size, unsigned long align,
+                            gfp_t gfp_mask, pgprot_t prot,
+                            int node, void *caller)
 {
         struct vm_struct *area;
         void *addr;
@@ -1495,8 +1498,8 @@ static void *__vmalloc_node(unsigned long size, gfp_t gfp_mask, pgprot_t prot,
         if (!size || (size >> PAGE_SHIFT) > totalram_pages)
                 return NULL;
 
-        area = __get_vm_area_node(size, VM_ALLOC, VMALLOC_START, VMALLOC_END,
-                                                node, gfp_mask, caller);
+        area = __get_vm_area_node(size, align, VM_ALLOC, VMALLOC_START,
+                                  VMALLOC_END, node, gfp_mask, caller);
 
         if (!area)
                 return NULL;
@@ -1515,7 +1518,7 @@ static void *__vmalloc_node(unsigned long size, gfp_t gfp_mask, pgprot_t prot,
 
 void *__vmalloc(unsigned long size, gfp_t gfp_mask, pgprot_t prot)
 {
-        return __vmalloc_node(size, gfp_mask, prot, -1,
+        return __vmalloc_node(size, 1, gfp_mask, prot, -1,
                                 __builtin_return_address(0));
 }
 EXPORT_SYMBOL(__vmalloc);
@@ -1531,7 +1534,7 @@ EXPORT_SYMBOL(__vmalloc);
  */
 void *vmalloc(unsigned long size)
 {
-        return __vmalloc_node(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL,
+        return __vmalloc_node(size, 1, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL,
                                         -1, __builtin_return_address(0));
 }
 EXPORT_SYMBOL(vmalloc);
@@ -1548,7 +1551,8 @@ void *vmalloc_user(unsigned long size)
         struct vm_struct *area;
         void *ret;
 
-        ret = __vmalloc_node(size, GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO,
+        ret = __vmalloc_node(size, SHMLBA,
+                             GFP_KERNEL | __GFP_HIGHMEM | __GFP_ZERO,
                              PAGE_KERNEL, -1, __builtin_return_address(0));
         if (ret) {
                 area = find_vm_area(ret);
@@ -1571,7 +1575,7 @@ EXPORT_SYMBOL(vmalloc_user);
  */
 void *vmalloc_node(unsigned long size, int node)
 {
-        return __vmalloc_node(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL,
+        return __vmalloc_node(size, 1, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL,
                                         node, __builtin_return_address(0));
 }
 EXPORT_SYMBOL(vmalloc_node);
@@ -1594,7 +1598,7 @@ EXPORT_SYMBOL(vmalloc_node);
 
 void *vmalloc_exec(unsigned long size)
 {
-        return __vmalloc_node(size, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL_EXEC,
+        return __vmalloc_node(size, 1, GFP_KERNEL | __GFP_HIGHMEM, PAGE_KERNEL_EXEC,
                               -1, __builtin_return_address(0));
 }
 
@@ -1615,7 +1619,7 @@ void *vmalloc_exec(unsigned long size)
  */
 void *vmalloc_32(unsigned long size)
 {
-        return __vmalloc_node(size, GFP_VMALLOC32, PAGE_KERNEL,
+        return __vmalloc_node(size, 1, GFP_VMALLOC32, PAGE_KERNEL,
                               -1, __builtin_return_address(0));
 }
 EXPORT_SYMBOL(vmalloc_32);
@@ -1632,7 +1636,7 @@ void *vmalloc_32_user(unsigned long size)
         struct vm_struct *area;
         void *ret;
 
-        ret = __vmalloc_node(size, GFP_VMALLOC32 | __GFP_ZERO, PAGE_KERNEL,
+        ret = __vmalloc_node(size, 1, GFP_VMALLOC32 | __GFP_ZERO, PAGE_KERNEL,
                              -1, __builtin_return_address(0));
         if (ret) {
                 area = find_vm_area(ret);
diff --git a/tools/perf/design.txt b/tools/perf/design.txt
index f1946d107b10..fdd42a824c98 100644
--- a/tools/perf/design.txt
+++ b/tools/perf/design.txt
@@ -455,3 +455,6 @@ will need at least this:
 
 If your architecture does have hardware capabilities, you can override the
 weak stub hw_perf_event_init() to register hardware counters.
+
+Architectures that have d-cache aliassing issues, such as Sparc and ARM,
+should select PERF_USE_VMALLOC in order to avoid these for perf mmap().