Messages in this thread Patch in this message | | | From | Roland McGrath <> | Subject | Re: Flushing whole page instead of work for ptrace | Date | Tue, 30 Nov 2010 15:32:50 -0800 (PST) |
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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
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