From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk0-f200.google.com (mail-qk0-f200.google.com [209.85.220.200]) by kanga.kvack.org (Postfix) with ESMTP id CB5E76B0006 for ; Thu, 19 Apr 2018 12:43:44 -0400 (EDT) Received: by mail-qk0-f200.google.com with SMTP id g138so3806278qke.22 for ; Thu, 19 Apr 2018 09:43:44 -0700 (PDT) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id d66si865951qkb.390.2018.04.19.09.43.43 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 19 Apr 2018 09:43:43 -0700 (PDT) Date: Thu, 19 Apr 2018 19:43:20 +0300 From: "Michael S. Tsirkin" Subject: Re: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM Message-ID: <20180419193554-mutt-send-email-mst@kernel.org> References: <3e65977e-53cd-bf09-bc4b-0ce40e9091fe@gmail.com> <20180418.134651.2225112489265654270.davem@davemloft.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Mikulas Patocka Cc: David Miller , Andrew Morton , linux-mm@kvack.org, eric.dumazet@gmail.com, edumazet@google.com, bhutchings@solarflare.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, jasowang@redhat.com, virtualization@lists.linux-foundation.org, dm-devel@redhat.com, Vlastimil Babka On Thu, Apr 19, 2018 at 12:12:38PM -0400, Mikulas Patocka wrote: > > > On Wed, 18 Apr 2018, Mikulas Patocka wrote: > > > > > > > On Wed, 18 Apr 2018, David Miller wrote: > > > > > From: Mikulas Patocka > > > Date: Wed, 18 Apr 2018 12:44:25 -0400 (EDT) > > > > > > > The structure net_device is followed by arbitrary driver-specific data > > > > (accessible with the function netdev_priv). And for virtio-net, these > > > > driver-specific data must be in DMA memory. > > > > > > And we are saying that this assumption is wrong and needs to be > > > corrected. > > > > So, try to find all the networking drivers that to DMA to the private > > area. > > > > The problem here is that kvzalloc usually returns DMA-able area, but it > > may return non-DMA area rarely, if the memory is too fragmented. So, we > > are in a situation, where some networking drivers will randomly fail. Go > > and find them. > > > > Mikulas > > Her I submit a patch that makes kvmalloc always use vmalloc if > CONFIG_DEBUG_VM is defined. > > > > > From: Mikulas Patocka > Subject: [PATCH] kvmalloc: always use vmalloc if CONFIG_DEBUG_VM > > The kvmalloc function tries to use kmalloc and falls back to vmalloc if > kmalloc fails. > > Unfortunatelly, some kernel code has bugs - it uses kvmalloc and then > uses DMA-API on the returned memory or frees it with kfree. Such bugs were > found in the virtio-net driver, dm-integrity or RHEL7 powerpc-specific > code. > > These bugs are hard to reproduce because vmalloc falls back to kmalloc > only if memory is fragmented. > > In order to detect these bugs reliably I submit this patch that changes > kvmalloc to always use vmalloc if CONFIG_DEBUG_VM is turned on. > > Signed-off-by: Mikulas Patocka Maybe make it conditional on CONFIG_DEBUG_SG too? Otherwise I think you just trigger a hard to debug memory corruption. > --- > mm/util.c | 2 ++ > 1 file changed, 2 insertions(+) > > Index: linux-2.6/mm/util.c > =================================================================== > --- linux-2.6.orig/mm/util.c 2018-04-18 15:46:23.000000000 +0200 > +++ linux-2.6/mm/util.c 2018-04-18 16:00:43.000000000 +0200 > @@ -395,6 +395,7 @@ EXPORT_SYMBOL(vm_mmap); > */ > void *kvmalloc_node(size_t size, gfp_t flags, int node) > { > +#ifndef CONFIG_DEBUG_VM > gfp_t kmalloc_flags = flags; > void *ret; > > @@ -426,6 +427,7 @@ void *kvmalloc_node(size_t size, gfp_t f > */ > if (ret || size <= PAGE_SIZE) > return ret; > +#endif > > return __vmalloc_node_flags_caller(size, node, flags, > __builtin_return_address(0));