| Message ID | 1390389916-8711-4-git-send-email-wangnan0@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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 <wangnan0@huawei.com> > Cc: <stable@vger.kernel.org> # 3.4+ > Cc: Eric Biederman <ebiederm@xmission.com> > Cc: Russell King <rmk+kernel@arm.linux.org.uk> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Geng Hui <hui.geng@huawei.com> > --- > 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/ >
On Thu, Jan 23, 2014 at 02:15:07PM -0500, Nicolas Pitre wrote: > 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. We already have support in the kernel to ignore memory below the calculated PHYS_OFFSET. See 571b14375019c3a66ef70d4d4a7083f4238aca30.
On Thu, 23 Jan 2014, Russell King - ARM Linux wrote: > On Thu, Jan 23, 2014 at 02:15:07PM -0500, Nicolas Pitre wrote: > > 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. > > We already have support in the kernel to ignore memory below the calculated > PHYS_OFFSET. See 571b14375019c3a66ef70d4d4a7083f4238aca30. Sure. Anyway what I'm suggesting above would require that the crash kernel be linked at a different virtual address for that to work. That's probably more trouble than simply mapping the otherwise still unmapped memory from the crashed kernel. Nicolas
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 */
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. Signed-off-by: Wang Nan <wangnan0@huawei.com> Cc: <stable@vger.kernel.org> # 3.4+ Cc: Eric Biederman <ebiederm@xmission.com> Cc: Russell King <rmk+kernel@arm.linux.org.uk> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Geng Hui <hui.geng@huawei.com> --- arch/arm/mm/init.c | 21 ++++++++++++++++++++- arch/arm/mm/mmu.c | 13 +++++++++++++ mm/page_alloc.c | 7 +++++-- 3 files changed, 38 insertions(+), 3 deletions(-)