Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757180Ab3CUGTn (ORCPT ); Thu, 21 Mar 2013 02:19:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:24149 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750950Ab3CUGTl (ORCPT ); Thu, 21 Mar 2013 02:19:41 -0400 Date: Thu, 21 Mar 2013 08:18:38 +0200 From: "Michael S. Tsirkin" To: "Michael R. Hines" Cc: Roland Dreier , Sean Hefty , Hal Rosenstock , Yishai Hadas , Christoph Lameter , linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org Subject: [PATCH] rdma: don't make pages writeable if not requiested Message-ID: <20130321061838.GA28319@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1989 Lines: 50 core/umem.c seems to get the arguments to get_user_pages in the reverse order: it sets writeable flag and breaks COW for MAP_SHARED if and only if hardware needs to write the page. This breaks memory overcommit for users such as KVM: each time we try to register a page to send it to remote, this breaks COW. It seems that for applications that only have REMOTE_READ permission, there is no reason to break COW at all. If the page that is COW has lots of copies, this makes the user process quickly exceed the cgroups memory limit. This makes RDMA mostly useless for virtualization, thus the stable tag. Reported-by: "Michael R. Hines" Cc: stable@vger.kernel.org Signed-off-by: Michael S. Tsirkin --- Note: compile-tested only, I don't have RDMA hardware at the moment. Michael, could you please try this patch (also fixing your usespace code not to request write access) and report? Note2: grep for get_user_pages in infiniband drivers turns up lots of users who set write to 1 unconditionally. These might be bugs too, should be checked. drivers/infiniband/core/umem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c index a841123..5929598 100644 --- a/drivers/infiniband/core/umem.c +++ b/drivers/infiniband/core/umem.c @@ -152,7 +152,7 @@ struct ib_umem *ib_umem_get(struct ib_ucontext *context, unsigned long addr, ret = get_user_pages(current, current->mm, cur_base, min_t(unsigned long, npages, PAGE_SIZE / sizeof (struct page *)), - 1, !umem->writable, page_list, vma_list); + !umem->writable, 1, page_list, vma_list); if (ret < 0) goto out; -- MST -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/