Roland McGrath wrote:
This is a VM question more than a ptrace question.
I can't give you any authoritative answers about the VM issues.
Documentation/cachetlb.txt says:
Any time the kernel writes to a page cache page, _OR_
the kernel is about to read from a page cache page and
user space shared/writable mappings of this page potentially
exist, this routine is called.
In your case, the kernel is only reading (write=0 passed to
access_process_vm and get_user_pages). In normal situations,
the page in question will have only a private and read-only
mapping in user space. So the call should not be required in
these cases--if the code can tell that's so.
Perhaps something like the following would be safe.
But you really need some VM folks to tell you for sure.
diff --git a/mm/memory.c b/mm/memory.c
index 02e48aa..2864ee7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1484,7 +1484,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
pages[i] = page;
flush_anon_page(vma, page, start);
- flush_dcache_page(page);
+ if ((vm_flags & VM_WRITE) || (vma->vm_flags & VM_SHARED)
+ flush_dcache_page(page);
}
if (vmas)
vmas[i] = vma;
Thanks,
Roland
Andrew any comment?
Thanks,
Michal
--
Michal Simek, Ing. (M.Eng)
PetaLogix - Linux Solutions for a Reconfigurable World
w: www.petalogix.com p: +61-7-30090663,+42-0-721842854 f: +61-7-30090663
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