On 1 June 2015 at 11:53, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> Hi Ard,
>
> Sorry for the silence on this.
>
> On Mon, May 11, 2015 at 07:41:54AM +0100, Ard Biesheuvel wrote:
>> Currently, the FDT blob needs to be in the same 512 MB region as
>> the kernel, so that it can be mapped into the kernel virtual memory
>> space very early on using a minimal set of statically allocated
>> translation tables.
>>
>> Now that we have early fixmap support, we can relax this restriction,
>> by moving the permanent FDT mapping to the fixmap region instead.
>> This way, the FDT blob may be anywhere in memory.
>>
>> This also moves the vetting of the FDT to mmu.c, since the early
>> init code in head.S does not handle mapping of the FDT anymore.
>> At the same time, fix up some comments in head.S that have gone stale.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
>
> The patch looks good to me. I've just given this some testing loading
> DTBs at weird offsets and large disances from the kernel, and that seems
> to work, so:
>
> Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>
> Tested-by: Mark Rutland <mark.rutland@xxxxxxx>
>
Thank you.
I noticed that I forgot to make the Documentation change you requested
last time around, so I will roll that into the next version (with your
tags).
--
Ard.
>> ---
>> Documentation/arm64/booting.txt | 13 ++++----
>> arch/arm64/include/asm/boot.h | 14 +++++++++
>> arch/arm64/include/asm/fixmap.h | 15 ++++++++++
>> arch/arm64/include/asm/mmu.h | 1 +
>> arch/arm64/kernel/head.S | 39 +-----------------------
>> arch/arm64/kernel/setup.c | 30 +++++++------------
>> arch/arm64/mm/Makefile | 2 ++
>> arch/arm64/mm/init.c | 1 -
>> arch/arm64/mm/mmu.c | 66 +++++++++++++++++++++++++++++++++++++++++
>> 9 files changed, 117 insertions(+), 64 deletions(-)
>> create mode 100644 arch/arm64/include/asm/boot.h
>>
>> diff --git a/Documentation/arm64/booting.txt b/Documentation/arm64/booting.txt
>> index f3c05b5f9f08..53f18e13d51c 100644
>> --- a/Documentation/arm64/booting.txt
>> +++ b/Documentation/arm64/booting.txt
>> @@ -45,11 +45,14 @@ sees fit.)
>>
>> Requirement: MANDATORY
>>
>> -The device tree blob (dtb) must be placed on an 8-byte boundary within
>> -the first 512 megabytes from the start of the kernel image and must not
>> -cross a 2-megabyte boundary. This is to allow the kernel to map the
>> -blob using a single section mapping in the initial page tables.
>> -
>> +The device tree blob (dtb) must be placed on an 8-byte boundary and must
>> +not exceed 2 megabytes in size. Since the dtb will be mapped cacheable using
>> +blocks of up to 2 megabytes in size, it should not be placed within 2 megabytes
>> +of memreserves or other special carveouts that may be mapped with non-matching
>> +attributes.
>> +
>> +NOTE: versions prior to v4.2 also require that the DTB be placed within
>> +the 512 MB region starting at text_offset bytes below the kernel Image.
>>
>> 3. Decompress the kernel image
>> ------------------------------
>> diff --git a/arch/arm64/include/asm/boot.h b/arch/arm64/include/asm/boot.h
>> new file mode 100644
>> index 000000000000..81151b67b26b
>> --- /dev/null
>> +++ b/arch/arm64/include/asm/boot.h
>> @@ -0,0 +1,14 @@
>> +
>> +#ifndef __ASM_BOOT_H
>> +#define __ASM_BOOT_H
>> +
>> +#include <asm/sizes.h>
>> +
>> +/*
>> + * arm64 requires the DTB to be 8 byte aligned and
>> + * not exceed 2MB in size.
>> + */
>> +#define MIN_FDT_ALIGN 8
>> +#define MAX_FDT_SIZE SZ_2M
>> +
>> +#endif
>> diff --git a/arch/arm64/include/asm/fixmap.h b/arch/arm64/include/asm/fixmap.h
>> index 95e6b6dcbe37..c0739187a920 100644
>> --- a/arch/arm64/include/asm/fixmap.h
>> +++ b/arch/arm64/include/asm/fixmap.h
>> @@ -17,6 +17,7 @@
>>
>> #ifndef __ASSEMBLY__
>> #include <linux/kernel.h>
>> +#include <asm/boot.h>
>> #include <asm/page.h>
>>
>> /*
>> @@ -32,6 +33,20 @@
>> */
>> enum fixed_addresses {
>> FIX_HOLE,
>> +
>> + /*
>> + * Reserve a virtual window for the FDT that is 2 MB larger than the
>> + * maximum supported size, and put it at the top of the fixmap region.
>> + * The additional space ensures that any FDT that does not exceed
>> + * MAX_FDT_SIZE can be mapped regardless of whether it crosses any
>> + * 2 MB alignment boundaries.
>> + *
>> + * Keep this at the top so it remains 2 MB aligned.
>> + */
>> +#define FIX_FDT_SIZE (MAX_FDT_SIZE + SZ_2M)
>> + FIX_FDT_END,
>> + FIX_FDT = FIX_FDT_END + FIX_FDT_SIZE / PAGE_SIZE - 1,
>> +
>> FIX_EARLYCON_MEM_BASE,
>> FIX_TEXT_POKE0,
>> __end_of_permanent_fixed_addresses,
>> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
>> index 3d311761e3c2..79fcfb048884 100644
>> --- a/arch/arm64/include/asm/mmu.h
>> +++ b/arch/arm64/include/asm/mmu.h
>> @@ -34,5 +34,6 @@ extern void init_mem_pgprot(void);
>> extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys,
>> unsigned long virt, phys_addr_t size,
>> pgprot_t prot);
>> +extern void *fixmap_remap_fdt(phys_addr_t dt_phys);
>>
>> #endif
>> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
>> index 19f915e8f6e0..30cffc5e7402 100644
>> --- a/arch/arm64/kernel/head.S
>> +++ b/arch/arm64/kernel/head.S
>> @@ -237,8 +237,6 @@ ENTRY(stext)
>> bl el2_setup // Drop to EL1, w20=cpu_boot_mode
>> adrp x24, __PHYS_OFFSET
>> bl set_cpu_boot_mode_flag
>> -
>> - bl __vet_fdt
>> bl __create_page_tables // x25=TTBR0, x26=TTBR1
>> /*
>> * The following calls CPU setup code, see arch/arm64/mm/proc.S for
>> @@ -270,24 +268,6 @@ preserve_boot_args:
>> ENDPROC(preserve_boot_args)
>>
>> /*
>> - * Determine validity of the x21 FDT pointer.
>> - * The dtb must be 8-byte aligned and live in the first 512M of memory.
>> - */
>> -__vet_fdt:
>> - tst x21, #0x7
>> - b.ne 1f
>> - cmp x21, x24
>> - b.lt 1f
>> - mov x0, #(1 << 29)
>> - add x0, x0, x24
>> - cmp x21, x0
>> - b.ge 1f
>> - ret
>> -1:
>> - mov x21, #0
>> - ret
>> -ENDPROC(__vet_fdt)
>> -/*
>> * Macro to create a table entry to the next page.
>> *
>> * tbl: page table address
>> @@ -348,8 +328,7 @@ ENDPROC(__vet_fdt)
>> * required to get the kernel running. The following sections are required:
>> * - identity mapping to enable the MMU (low address, TTBR0)
>> * - first few MB of the kernel linear mapping to jump to once the MMU has
>> - * been enabled, including the FDT blob (TTBR1)
>> - * - pgd entry for fixed mappings (TTBR1)
>> + * been enabled
>> */
>> __create_page_tables:
>> adrp x25, idmap_pg_dir
>> @@ -439,22 +418,6 @@ __create_page_tables:
>> create_block_map x0, x7, x3, x5, x6
>>
>> /*
>> - * Map the FDT blob (maximum 2MB; must be within 512MB of
>> - * PHYS_OFFSET).
>> - */
>> - mov x3, x21 // FDT phys address
>> - and x3, x3, #~((1 << 21) - 1) // 2MB aligned
>> - mov x6, #PAGE_OFFSET
>> - sub x5, x3, x24 // subtract PHYS_OFFSET
>> - tst x5, #~((1 << 29) - 1) // within 512MB?
>> - csel x21, xzr, x21, ne // zero the FDT pointer
>> - b.ne 1f
>> - add x5, x5, x6 // __va(FDT blob)
>> - add x6, x5, #1 << 21 // 2MB for the FDT blob
>> - sub x6, x6, #1 // inclusive range
>> - create_block_map x0, x7, x3, x5, x6
>> -1:
>> - /*
>> * Since the page tables have been populated with non-cacheable
>> * accesses (MMU disabled), invalidate the idmap and swapper page
>> * tables again to remove any speculatively loaded cache lines.
>> diff --git a/arch/arm64/kernel/setup.c b/arch/arm64/kernel/setup.c
>> index 74753132c3ac..770ae9dc5a75 100644
>> --- a/arch/arm64/kernel/setup.c
>> +++ b/arch/arm64/kernel/setup.c
>> @@ -105,18 +105,6 @@ static struct resource mem_res[] = {
>> #define kernel_code mem_res[0]
>> #define kernel_data mem_res[1]
>>
>> -void __init early_print(const char *str, ...)
>> -{
>> - char buf[256];
>> - va_list ap;
>> -
>> - va_start(ap, str);
>> - vsnprintf(buf, sizeof(buf), str, ap);
>> - va_end(ap);
>> -
>> - printk("%s", buf);
>> -}
>> -
>> /*
>> * The recorded values of x0 .. x3 upon kernel entry.
>> */
>> @@ -326,12 +314,14 @@ static void __init setup_processor(void)
>>
>> static void __init setup_machine_fdt(phys_addr_t dt_phys)
>> {
>> - if (!dt_phys || !early_init_dt_scan(phys_to_virt(dt_phys))) {
>> - early_print("\n"
>> - "Error: invalid device tree blob at physical address 0x%p (virtual address 0x%p)\n"
>> - "The dtb must be 8-byte aligned and passed in the first 512MB of memory\n"
>> - "\nPlease check your bootloader.\n",
>> - dt_phys, phys_to_virt(dt_phys));
>> + void *dt_virt = fixmap_remap_fdt(dt_phys);
>> +
>> + if (!dt_virt || !early_init_dt_scan(dt_virt)) {
>> + pr_crit("\n"
>> + "Error: invalid device tree blob at physical address %pa (virtual address 0x%p)\n"
>> + "The dtb must be 8-byte aligned and must not exceed 2 MB in size\n"
>> + "\nPlease check your bootloader.",
>> + &dt_phys, dt_virt);
>>
>> while (true)
>> cpu_relax();
>> @@ -374,8 +364,6 @@ void __init setup_arch(char **cmdline_p)
>> {
>> setup_processor();
>>
>> - setup_machine_fdt(__fdt_pointer);
>> -
>> init_mm.start_code = (unsigned long) _text;
>> init_mm.end_code = (unsigned long) _etext;
>> init_mm.end_data = (unsigned long) _edata;
>> @@ -386,6 +374,8 @@ void __init setup_arch(char **cmdline_p)
>> early_fixmap_init();
>> early_ioremap_init();
>>
>> + setup_machine_fdt(__fdt_pointer);
>> +
>> parse_early_param();
>>
>> /*
>> diff --git a/arch/arm64/mm/Makefile b/arch/arm64/mm/Makefile
>> index 773d37a14039..9d84feb41a16 100644
>> --- a/arch/arm64/mm/Makefile
>> +++ b/arch/arm64/mm/Makefile
>> @@ -4,3 +4,5 @@ obj-y := dma-mapping.o extable.o fault.o init.o \
>> context.o proc.o pageattr.o
>> obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
>> obj-$(CONFIG_ARM64_PTDUMP) += dump.o
>> +
>> +CFLAGS_mmu.o := -I$(srctree)/scripts/dtc/libfdt/
>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
>> index 89a05f467ffb..597831bdddf3 100644
>> --- a/arch/arm64/mm/init.c
>> +++ b/arch/arm64/mm/init.c
>> @@ -170,7 +170,6 @@ void __init arm64_memblock_init(void)
>> memblock_reserve(__virt_to_phys(initrd_start), initrd_end - initrd_start);
>> #endif
>>
>> - early_init_fdt_reserve_self();
>> early_init_fdt_scan_reserved_mem();
>>
>> /* 4GB maximum for 32-bit only capable devices */
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index 5b8b664422d3..82d3435bf14f 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -21,6 +21,7 @@
>> #include <linux/kernel.h>
>> #include <linux/errno.h>
>> #include <linux/init.h>
>> +#include <linux/libfdt.h>
>> #include <linux/mman.h>
>> #include <linux/nodemask.h>
>> #include <linux/memblock.h>
>> @@ -643,3 +644,68 @@ void __set_fixmap(enum fixed_addresses idx,
>> flush_tlb_kernel_range(addr, addr+PAGE_SIZE);
>> }
>> }
>> +
>> +void *__init fixmap_remap_fdt(phys_addr_t dt_phys)
>> +{
>> + const u64 dt_virt_base = __fix_to_virt(FIX_FDT);
>> + pgprot_t prot = PAGE_KERNEL | PTE_RDONLY;
>> + int granularity, size, offset;
>> + void *dt_virt;
>> +
>> + /*
>> + * Check whether the physical FDT address is set and meets the minimum
>> + * alignment requirement. Since we are relying on MIN_FDT_ALIGN to be
>> + * at least 8 bytes so that we can always access the size field of the
>> + * FDT header after mapping the first chunk, double check here if that
>> + * is indeed the case.
>> + */
>> + BUILD_BUG_ON(MIN_FDT_ALIGN < 8);
>> + if (!dt_phys || dt_phys % MIN_FDT_ALIGN)
>> + return NULL;
>> +
>> + /*
>> + * Make sure that the FDT region can be mapped without the need to
>> + * allocate additional translation table pages, so that it is safe
>> + * to call create_mapping() this early.
>> + *
>> + * On 64k pages, the FDT will be mapped using PTEs, so we need to
>> + * be in the same PMD as the rest of the fixmap.
>> + * On 4k pages, we'll use section mappings for the FDT so we only
>> + * have to be in the same PUD.
>> + */
>> + BUILD_BUG_ON(dt_virt_base % SZ_2M);
>> +
>> + if (IS_ENABLED(CONFIG_ARM64_64K_PAGES)) {
>> + BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> PMD_SHIFT !=
>> + __fix_to_virt(FIX_BTMAP_BEGIN) >> PMD_SHIFT);
>> +
>> + granularity = PAGE_SIZE;
>> + } else {
>> + BUILD_BUG_ON(__fix_to_virt(FIX_FDT_END) >> PUD_SHIFT !=
>> + __fix_to_virt(FIX_BTMAP_BEGIN) >> PUD_SHIFT);
>> +
>> + granularity = PMD_SIZE;
>> + }
>> +
>> + offset = dt_phys % granularity;
>> + dt_virt = (void *)dt_virt_base + offset;
>> +
>> + /* map the first chunk so we can read the size from the header */
>> + create_mapping(round_down(dt_phys, granularity), dt_virt_base,
>> + granularity, prot);
>> +
>> + if (fdt_check_header(dt_virt) != 0)
>> + return NULL;
>> +
>> + size = fdt_totalsize(dt_virt);
>> + if (size > MAX_FDT_SIZE)
>> + return NULL;
>> +
>> + if (offset + size > granularity)
>> + create_mapping(round_down(dt_phys, granularity), dt_virt_base,
>> + round_up(offset + size, granularity), prot);
>> +
>> + memblock_reserve(dt_phys, size);
>> +
>> + return dt_virt;
>> +}
>> --
>> 1.9.1
>>
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