From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0188DC49ED7 for ; Mon, 16 Sep 2019 21:32:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C9E8B206C2 for ; Mon, 16 Sep 2019 21:32:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389196AbfIPVc4 (ORCPT ); Mon, 16 Sep 2019 17:32:56 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44234 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389236AbfIPVcz (ORCPT ); Mon, 16 Sep 2019 17:32:55 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 937A089F39E; Mon, 16 Sep 2019 21:32:55 +0000 (UTC) Received: from redhat.com (ovpn-122-216.rdu2.redhat.com [10.10.122.216]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0F3535D6B2; Mon, 16 Sep 2019 21:32:54 +0000 (UTC) Date: Mon, 16 Sep 2019 16:32:53 -0500 From: Bill O'Donnell To: Eric Sandeen Cc: linux-xfs@vger.kernel.org, darrick.wong@oracle.com Subject: Re: [PATCH] xfs: assure zeroed memory buffers for certain kmem allocations Message-ID: <20190916213253.GA13257@redhat.com> References: <20190916153504.30809-1-billodo@redhat.com> <5f1bcfbd-f16b-6d8a-416d-3a0639b9c7fe@sandeen.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5f1bcfbd-f16b-6d8a-416d-3a0639b9c7fe@sandeen.net> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.68]); Mon, 16 Sep 2019 21:32:55 +0000 (UTC) Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Mon, Sep 16, 2019 at 04:24:40PM -0500, Eric Sandeen wrote: > On 9/16/19 10:35 AM, Bill O'Donnell wrote: > > Guarantee zeroed memory buffers for cases where potential memory > > leak to disk can occur. In these cases, kmem_alloc is used and > > doesn't zero the buffer, opening the possibility of information > > leakage to disk. > > > > Introduce a xfs_buf_flag, _XBF_KMZ, to indicate a request for a zeroed > > buffer, and use existing infrastucture (xfs_buf_allocate_memory) to > > obtain the already zeroed buffer from kernel memory. > > > > This solution avoids the performance issue that would occur if a > > wholesale change to replace kmem_alloc with kmem_zalloc was done. > > > > Signed-off-by: Bill O'Donnell > > I think this can probably be further optimized by not obtaining zeroed > memory when we're about to fill the buffer from disk as the very > next step. Yep. I missed that redundancy. > > (in this case, xfs_buf_read_map calls xfs_buf_get_map and then immediately > reads the buffer from disk with _xfs_buf_read) xfs_buf_read_map adds > XBF_READ to the flags during this process. > > So I wonder if this can be simplified/optimized by just checking for XBF_READ > in xfs_buf_allocate_memory's flags, and if it's not set, then request > zeroed memory, because that indicates a buffer we'll be filling in from > memory and subsequently writing to disk. nod. > > -Eric > > > --- > > fs/xfs/xfs_buf.c | 8 ++++++-- > > fs/xfs/xfs_buf.h | 4 +++- > > 2 files changed, 9 insertions(+), 3 deletions(-) > > > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > > index 120ef99d09e8..916a3f782950 100644 > > --- a/fs/xfs/xfs_buf.c > > +++ b/fs/xfs/xfs_buf.c > > @@ -345,16 +345,19 @@ xfs_buf_allocate_memory( > > unsigned short page_count, i; > > xfs_off_t start, end; > > int error; > > + uint kmflag_mask = 0; > > > > /* > > * for buffers that are contained within a single page, just allocate > > * the memory from the heap - there's no need for the complexity of > > * page arrays to keep allocation down to order 0. > > */ > > + if (flags & _XBF_KMZ) > > + kmflag_mask |= KM_ZERO; > > size = BBTOB(bp->b_length); > > if (size < PAGE_SIZE) { > > int align_mask = xfs_buftarg_dma_alignment(bp->b_target); > > - bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS); > > + bp->b_addr = kmem_alloc_io(size, align_mask, KM_NOFS | kmflag_mask); > > if (!bp->b_addr) { > > /* low memory - use alloc_page loop instead */ > > goto use_alloc_page; > > @@ -391,7 +394,7 @@ xfs_buf_allocate_memory( > > struct page *page; > > uint retries = 0; > > retry: > > - page = alloc_page(gfp_mask); > > + page = alloc_page(gfp_mask | kmflag_mask); > > if (unlikely(page == NULL)) { > > if (flags & XBF_READ_AHEAD) { > > bp->b_page_count = i; > > @@ -683,6 +686,7 @@ xfs_buf_get_map( > > struct xfs_buf *new_bp; > > int error = 0; > > > > + flags |= _XBF_KMZ; > > error = xfs_buf_find(target, map, nmaps, flags, NULL, &bp); > > > > switch (error) { > > diff --git a/fs/xfs/xfs_buf.h b/fs/xfs/xfs_buf.h > > index f6ce17d8d848..416ff588240a 100644 > > --- a/fs/xfs/xfs_buf.h > > +++ b/fs/xfs/xfs_buf.h > > @@ -38,6 +38,7 @@ > > #define _XBF_PAGES (1 << 20)/* backed by refcounted pages */ > > #define _XBF_KMEM (1 << 21)/* backed by heap memory */ > > #define _XBF_DELWRI_Q (1 << 22)/* buffer on a delwri queue */ > > +#define _XBF_KMZ (1 << 23)/* zeroed buffer required */ > > > > typedef unsigned int xfs_buf_flags_t; > > > > @@ -54,7 +55,8 @@ typedef unsigned int xfs_buf_flags_t; > > { XBF_UNMAPPED, "UNMAPPED" }, /* ditto */\ > > { _XBF_PAGES, "PAGES" }, \ > > { _XBF_KMEM, "KMEM" }, \ > > - { _XBF_DELWRI_Q, "DELWRI_Q" } > > + { _XBF_DELWRI_Q, "DELWRI_Q" }, \ > > + { _XBF_KMZ, "KMEM_Z" } > > > > > > /* > >