On 12/10, Linus Torvalds wrote: > > On Tue, Dec 10, 2013 at 11:18 AM, Oleg Nesterov <o...@redhat.com> wrote: > > > > Well, if we use get_user_pages() we have vma for free. > > No we don't. get_user_pages() is expensive as hell.
I understand, I said "if we use get_user_pages()". > We'd be *much* better off using get_user_pages_fast() if possible - > and I bet _is_ possible in 99% of all cases. We can't. get_user_pages_fast() takes mmap_sem. Perhaps we can do something, say add FOLL_FAST_ONLY, but until then we need the 1st get_user_pages(write => 0) anyway. > > But I am not sure about "and verify it for now" above. Do you mean > > that uprobe_write_opcode() should do another valid_vma() ? > > No. I think we should just do something like > > if (vma->vm_flags & (VM_SHARED | VM_HUGETLB)) > return -EINVAL; OK, but WARN_ON(VM_SHARED | VM_HUGETLB) looks better imho. Because this should not happen. > then just looking up the page table _once_ - instead of > three times - would make the code safer and faster. Unlikely we can do this only once... At least I do not see how. > It *may* be safe if callers do > all the right black magic, but it's by no means obvious. I agree, this needs more documentation in any case. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
