[PATCH 2/8] arm64: use fixmap region for permanent FDT mapping
Mark Rutland
mark.rutland at arm.com
Mon Jun 1 02:53:33 PDT 2015
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 at linaro.org>
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 at arm.com>
Tested-by: Mark Rutland <mark.rutland at arm.com>
Thanks,
Mark.
> ---
> 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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