Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932206AbaAWTPO (ORCPT ); Thu, 23 Jan 2014 14:15:14 -0500 Received: from relais.videotron.ca ([24.201.245.36]:45558 "EHLO relais.videotron.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755303AbaAWTPJ (ORCPT ); Thu, 23 Jan 2014 14:15:09 -0500 MIME-version: 1.0 Content-transfer-encoding: 7BIT Content-type: TEXT/PLAIN; CHARSET=US-ASCII Date: Thu, 23 Jan 2014 14:15:07 -0500 (EST) From: Nicolas Pitre To: Wang Nan Cc: kexec@lists.infradead.org, Eric Biederman , Russell King , Andrew Morton , Geng Hui , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org Subject: Re: [PATCH 3/3] ARM: allow kernel to be loaded in middle of phymem In-reply-to: <1390389916-8711-4-git-send-email-wangnan0@huawei.com> Message-id: References: <1390389916-8711-1-git-send-email-wangnan0@huawei.com> <1390389916-8711-4-git-send-email-wangnan0@huawei.com> User-Agent: Alpine 2.11 (LFD 23 2013-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 22 Jan 2014, Wang Nan wrote: > This patch allows the kernel to be loaded at the middle of kernel awared > physical memory. Before this patch, users must use mem= or device tree to cheat > kernel about the start address of physical memory. > > This feature is useful in some special cases, for example, building a crash > dump kernel. Without it, kernel command line, atag and devicetree must be > adjusted carefully, sometimes is impossible. With CONFIG_PATCH_PHYS_VIRT the value for PHYS_OFFSET is determined dynamically by rounding down the kernel image start address to the previous 16MB boundary. In the case of a crash kernel, this might be cleaner to simply readjust __pv_phys_offset during early boot and call fixup_pv_table(), and then reserve away the memory from the previous kernel. That will let you access that memory directly (with gdb for example) and no pointer address translation will be required. > Signed-off-by: Wang Nan > Cc: # 3.4+ > Cc: Eric Biederman > Cc: Russell King > Cc: Andrew Morton > Cc: Geng Hui > --- > arch/arm/mm/init.c | 21 ++++++++++++++++++++- > arch/arm/mm/mmu.c | 13 +++++++++++++ > mm/page_alloc.c | 7 +++++-- > 3 files changed, 38 insertions(+), 3 deletions(-) > > diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c > index 3e8f106..4952726 100644 > --- a/arch/arm/mm/init.c > +++ b/arch/arm/mm/init.c > @@ -334,9 +334,28 @@ void __init arm_memblock_init(struct meminfo *mi, > { > int i; > > - for (i = 0; i < mi->nr_banks; i++) > + for (i = 0; i < mi->nr_banks; i++) { > memblock_add(mi->bank[i].start, mi->bank[i].size); > > + /* > + * In some special case, for example, building a crushdump > + * kernel, we want the kernel to be loaded in the middle of > + * physical memory. In such case, the physical memory before > + * PHYS_OFFSET is awkward: it can't get directly mapped > + * (because its address will be smaller than PAGE_OFFSET, > + * disturbs user address space) also can't be mapped as > + * HighMem. We reserve such pages here. The only way to access > + * those pages is ioremap. > + */ > + if (mi->bank[i].start < PHYS_OFFSET) { > + unsigned long reserv_size = PHYS_OFFSET - > + mi->bank[i].start; > + if (reserv_size > mi->bank[i].size) > + reserv_size = mi->bank[i].size; > + memblock_reserve(mi->bank[i].start, reserv_size); > + } > + } > + > /* Register the kernel text, kernel data and initrd with memblock. */ > #ifdef CONFIG_XIP_KERNEL > memblock_reserve(__pa(_sdata), _end - _sdata); > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c > index 580ef2d..2a17c24 100644 > --- a/arch/arm/mm/mmu.c > +++ b/arch/arm/mm/mmu.c > @@ -1308,6 +1308,19 @@ static void __init map_lowmem(void) > if (start >= end) > break; > > + /* > + * If this memblock contain memory before PAGE_OFFSET, memory > + * before PAGE_OFFSET should't get directly mapped, see code > + * in create_mapping(). However, memory after PAGE_OFFSET is > + * occupyed by kernel and still need to be mapped. > + */ > + if (__phys_to_virt(start) < PAGE_OFFSET) { > + if (__phys_to_virt(end) > PAGE_OFFSET) > + start = __virt_to_phys(PAGE_OFFSET); > + else > + break; > + } > + > map.pfn = __phys_to_pfn(start); > map.virtual = __phys_to_virt(start); > map.length = end - start; > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 5248fe0..d2959e3 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4840,10 +4840,13 @@ static void __init_refok alloc_node_mem_map(struct pglist_data *pgdat) > */ > if (pgdat == NODE_DATA(0)) { > mem_map = NODE_DATA(0)->node_mem_map; > -#ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP > + /* > + * In case of CONFIG_HAVE_MEMBLOCK_NODE_MAP or when kernel > + * loaded at the middle of physical memory, mem_map should > + * be adjusted. > + */ > if (page_to_pfn(mem_map) != pgdat->node_start_pfn) > mem_map -= (pgdat->node_start_pfn - ARCH_PFN_OFFSET); > -#endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */ > } > #endif > #endif /* CONFIG_FLAT_NODE_MEM_MAP */ > -- > 1.8.4 > > -- > 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/ > -- 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/