On 04/16/14 15:37, David Miller wrote:
From: Oleg Nesterov oleg@redhat.com Date: Wed, 16 Apr 2014 21:18:25 +0200
The last question... area->page = alloc_page(GFP_HIGHUSER), and I am not sure that arch/arm/mm/highmem.c:kmap_atomic() can't break the aliasing, __fix_to_virt() in this case will use the same (per-cpu) idx.
Looks like, __kunmap_atomic()->__cpuc_flush_dcache_area() should take care, but could you please ack/nack my understanding?
Good point, it might therefore make sense to use a low-mem page.
The following test code seems to have the same problems with stale user icache. It works if I put the dcache flush back in. Am I missing something?
-dl
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index 04709b6..10ad973 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -34,6 +34,7 @@ #include <linux/ptrace.h> /* user_enable_single_step */ #include <linux/kdebug.h> /* notifier mechanism */ #include "../../mm/internal.h" /* munlock_vma_page */ +#include <linux/mman.h> #include <linux/percpu-rwsem.h> #include <linux/task_work.h>
@@ -1141,7 +1142,7 @@ static int xol_add_vma(struct mm_struct *mm, struct xol_area *area) if (!area->vaddr) { /* Try to map as high as possible, this is only a hint. */ area->vaddr = get_unmapped_area(NULL, TASK_SIZE - PAGE_SIZE, - PAGE_SIZE, 0, 0); + PAGE_SIZE, page_to_pfn(area->page), MAP_SHARED); if (area->vaddr & ~PAGE_MASK) { ret = area->vaddr; goto fail; @@ -1175,7 +1176,7 @@ static struct xol_area *__create_xol_area(unsigned long vaddr) if (!area->bitmap) goto free_area;
- area->page = alloc_page(GFP_HIGHUSER); + area->page = alloc_page(GFP_USER); if (!area->page) goto free_bitmap;
@@ -1299,11 +1300,8 @@ static unsigned long xol_get_insn_slot(struct uprobe *uprobe) /* Initialize the slot */ copy_to_page(area->page, xol_vaddr, &uprobe->arch.ixol, sizeof(uprobe->arch.ixol)); - /* - * We probably need flush_icache_user_range() but it needs vma. - * This should work on supported architectures too. - */ - flush_dcache_page(area->page); +/* Temporary hard-core icache flush for testing */ + __flush_icache_all();
return xol_vaddr; }