Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S979269AbdDXXSz (ORCPT ); Mon, 24 Apr 2017 19:18:55 -0400 Received: from mail-oi0-f51.google.com ([209.85.218.51]:35602 "EHLO mail-oi0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S977740AbdDXXSs (ORCPT ); Mon, 24 Apr 2017 19:18:48 -0400 MIME-Version: 1.0 In-Reply-To: <20170424230738.GA11734@x1> References: <20170419133630.GA2311@x1> <20170420132632.GD2311@x1> <20170424230738.GA11734@x1> From: Dan Williams Date: Mon, 24 Apr 2017 16:18:47 -0700 Message-ID: Subject: Re: KASLR causes intermittent boot failures on some systems To: Baoquan He Cc: Thomas Garnier , Jeff Moyer , Ingo Molnar , LKML , "linux-nvdimm@lists.01.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1796 Lines: 41 On Mon, Apr 24, 2017 at 4:07 PM, Baoquan He wrote: > On 04/24/17 at 01:52pm, Dan Williams wrote: [..] >> When using the memmap= parameter we're using this call by default: >> >> } else if (pmem_should_map_pages(dev)) { >> addr = devm_memremap_pages(dev, &nsio->res, >> &q->q_usage_counter, NULL); >> pmem->pfn_flags |= PFN_MAP; >> } else >> >> ...where we are assuming that the memmap= parameter does not specify a >> range-size that will exhaust all of system-memory just to hold the >> struct page array. > > Yeah, according to my debugging tracking, it goes as Dan said. And the > is_ram is REGION_DISJOINT. And till arch_add_memory, the parameters > passed to arch_add_memory are "arch_add_memory, align_start:0x10000000000, align_size:0x3000000000", > seems it's going well. > > Hi Dan, > > I am always confused that in devm_memremap_pages, the passed in > parameter altmap is NULL, while it used devres_alloc_node to allocate a > page_map and that page_map contained a altmap instance, not pointer. > Then the addr range were inserted into pgmap_radix with value of > page_map. Why later in __add_pages, to_vmem_altmap() return NULL > according to my debugging code? We expect altmap to always be NULL in this case. The only time it is not NULL is when the namespace is configured to allocate the struct page array from capacity on the namespace itself. I.e. instead of allocating struct page from page allocator pages the driver creates an altmap and vmemmap_populate_hugepages() uses that to allocate the array from "alternate" capacity. You can force this by running: ndctl create-namespace -f -e namespace0.0 -m memory -M dev ...which says "put the struct page map on the device".