[PATCH v2 2/2] ARM: move device tree mapping out of linear region
Joel Stanley
joel at jms.id.au
Wed Oct 28 08:05:28 EDT 2020
On Wed, 28 Oct 2020 at 09:19, Marek Szyprowski <m.szyprowski at samsung.com> wrote:
>
> Hi,
>
> On 07.10.2020 10:39, Ard Biesheuvel wrote:
> > On ARM, setting up the linear region is tricky, given the constraints
> > around placement and alignment of the memblocks, and how the kernel
> > itself as well as the DT are placed in physical memory.
> >
> > Let's simplify matters a bit, by moving the device tree mapping to the
> > top of the address space, right between the end of the vmalloc region
> > and the start of the the fixmap region, and create a read-only mapping
> > for it that is independent of the size of the linear region, and how it
> > is organized.
> >
> > Since this region was formerly used as a guard region, which will now be
> > populated fully on LPAE builds by this read-only mapping (which will
> > still be able to function as a guard region for stray writes), bump the
> > start of the [underutilized] fixmap region by 512 KB as well, to ensure
> > that there is always a proper guard region here. Doing so still leaves
> > ample room for the fixmap space, even with NR_CPUS set to its maximum
> > value of 32.
> >
> > Tested-by: Linus Walleij <linus.walleij at linaro.org>
> > Reviewed-by: Linus Walleij <linus.walleij at linaro.org>
> > Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
>
> This patch landed in linux-next 20201028 as commit 7a1be318f579 ("ARM:
> 9012/1: move device tree mapping out of linear region"). Sadly it broke
> booting almost all Samsung Exynos-based boards. The only one which
> booted, used an appended device tree. I can provide more information if
> needed, just let me know what to check. "Starting kernel ..." is the
> last message I see here. No output from earlycon.
A bisection lead me to this patch after the next-20201028 failed to
boot on the aspeed systems in testing (aspeed_g5_defconfig).
You can reproduce this with today's next and qemu 5.1:
qemu-system-arm -M romulus-bmc -nographic \
-kernel arch/arm/boot/zImage \
-dtb arch/arm/boot/dts/aspeed-bmc-opp-romulus.dtb \
-initrd any-old-file
It requires the initrd option to reproduce, but the initrd doesn't
need to be valid as we don't make it that far.
There is no output but attaching gdb shows the kernel is stuck in
setup_machine_tags. (If we enable CONFIG_ATAGS it is instead stuck in
calibrate_delay).
(gdb) bt
#0 setup_machine_tags (machine_nr=<optimized out>,
__atags_vaddr=<optimized out>) at ../arch/arm/kernel/atags.h:12
#1 setup_arch (cmdline_p=0x80c01fc4) at ../arch/arm/kernel/setup.c:1100
#2 0x80b00d2c in start_kernel () at ../init/main.c:862
#3 0x00000000 in ?? ()
Reverting 7a1be318f579 on top of next allowed the system to boot again.
Cheers,
Joel
>
> > ---
> > Documentation/arm/memory.rst | 7 ++++++-
> > arch/arm/include/asm/fixmap.h | 2 +-
> > arch/arm/include/asm/memory.h | 5 +++++
> > arch/arm/kernel/head.S | 5 ++---
> > arch/arm/kernel/setup.c | 11 ++++++++---
> > arch/arm/mm/init.c | 1 -
> > arch/arm/mm/mmu.c | 20 ++++++++++++++------
> > arch/arm/mm/pv-fixup-asm.S | 4 ++--
> > 8 files changed, 38 insertions(+), 17 deletions(-)
> >
> > diff --git a/Documentation/arm/memory.rst b/Documentation/arm/memory.rst
> > index 0521b4ce5c96..34bb23c44a71 100644
> > --- a/Documentation/arm/memory.rst
> > +++ b/Documentation/arm/memory.rst
> > @@ -45,9 +45,14 @@ fffe8000 fffeffff DTCM mapping area for platforms with
> > fffe0000 fffe7fff ITCM mapping area for platforms with
> > ITCM mounted inside the CPU.
> >
> > -ffc00000 ffefffff Fixmap mapping region. Addresses provided
> > +ffc80000 ffefffff Fixmap mapping region. Addresses provided
> > by fix_to_virt() will be located here.
> >
> > +ffc00000 ffc7ffff Guard region
> > +
> > +ff800000 ffbfffff Permanent, fixed read-only mapping of the
> > + firmware provided DT blob
> > +
> > fee00000 feffffff Mapping of PCI I/O space. This is a static
> > mapping within the vmalloc space.
> >
> > diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h
> > index fc56fc3e1931..9575b404019c 100644
> > --- a/arch/arm/include/asm/fixmap.h
> > +++ b/arch/arm/include/asm/fixmap.h
> > @@ -2,7 +2,7 @@
> > #ifndef _ASM_FIXMAP_H
> > #define _ASM_FIXMAP_H
> >
> > -#define FIXADDR_START 0xffc00000UL
> > +#define FIXADDR_START 0xffc80000UL
> > #define FIXADDR_END 0xfff00000UL
> > #define FIXADDR_TOP (FIXADDR_END - PAGE_SIZE)
> >
> > diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
> > index 99035b5891ef..ad9dcf4f751d 100644
> > --- a/arch/arm/include/asm/memory.h
> > +++ b/arch/arm/include/asm/memory.h
> > @@ -67,6 +67,10 @@
> > */
> > #define XIP_VIRT_ADDR(physaddr) (MODULES_VADDR + ((physaddr) & 0x000fffff))
> >
> > +#define FDT_FIXED_BASE UL(0xff800000)
> > +#define FDT_FIXED_SIZE (2 * PMD_SIZE)
> > +#define FDT_VIRT_ADDR(physaddr) ((void *)(FDT_FIXED_BASE | (physaddr) % PMD_SIZE))
> > +
> > #if !defined(CONFIG_SMP) && !defined(CONFIG_ARM_LPAE)
> > /*
> > * Allow 16MB-aligned ioremap pages
> > @@ -107,6 +111,7 @@ extern unsigned long vectors_base;
> > #define MODULES_VADDR PAGE_OFFSET
> >
> > #define XIP_VIRT_ADDR(physaddr) (physaddr)
> > +#define FDT_VIRT_ADDR(physaddr) (physaddr)
> >
> > #endif /* !CONFIG_MMU */
> >
> > diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
> > index f8904227e7fd..9b18d8c66129 100644
> > --- a/arch/arm/kernel/head.S
> > +++ b/arch/arm/kernel/head.S
> > @@ -275,9 +275,8 @@ __create_page_tables:
> > */
> > mov r0, r2, lsr #SECTION_SHIFT
> > movs r0, r0, lsl #SECTION_SHIFT
> > - subne r3, r0, r8
> > - addne r3, r3, #PAGE_OFFSET
> > - addne r3, r4, r3, lsr #(SECTION_SHIFT - PMD_ORDER)
> > + ldrne r3, =FDT_FIXED_BASE >> (SECTION_SHIFT - PMD_ORDER)
> > + addne r3, r3, r4
> > orrne r6, r7, r0
> > strne r6, [r3], #1 << PMD_ORDER
> > addne r6, r6, #1 << SECTION_SHIFT
> > diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> > index 58e56e23a19a..c08574cad748 100644
> > --- a/arch/arm/kernel/setup.c
> > +++ b/arch/arm/kernel/setup.c
> > @@ -18,6 +18,7 @@
> > #include <linux/of_platform.h>
> > #include <linux/init.h>
> > #include <linux/kexec.h>
> > +#include <linux/libfdt.h>
> > #include <linux/of_fdt.h>
> > #include <linux/cpu.h>
> > #include <linux/interrupt.h>
> > @@ -90,7 +91,6 @@ unsigned int cacheid __read_mostly;
> > EXPORT_SYMBOL(cacheid);
> >
> > unsigned int __atags_pointer __initdata;
> > -void *atags_vaddr __initdata;
> >
> > unsigned int system_rev;
> > EXPORT_SYMBOL(system_rev);
> > @@ -1078,13 +1078,18 @@ void __init hyp_mode_check(void)
> > void __init setup_arch(char **cmdline_p)
> > {
> > const struct machine_desc *mdesc = NULL;
> > + void *atags_vaddr;
> >
> > if (__atags_pointer)
> > - atags_vaddr = phys_to_virt(__atags_pointer);
> > + atags_vaddr = FDT_VIRT_ADDR(__atags_pointer);
> >
> > setup_processor();
> > - if (atags_vaddr)
> > + if (atags_vaddr) {
> > mdesc = setup_machine_fdt(atags_vaddr);
> > + if (mdesc)
> > + memblock_reserve(__atags_pointer,
> > + fdt_totalsize(atags_vaddr));
> > + }
> > if (!mdesc)
> > mdesc = setup_machine_tags(atags_vaddr, __machine_arch_type);
> > if (!mdesc) {
> > diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
> > index 000c1b48e973..652a87bd065c 100644
> > --- a/arch/arm/mm/init.c
> > +++ b/arch/arm/mm/init.c
> > @@ -223,7 +223,6 @@ void __init arm_memblock_init(const struct machine_desc *mdesc)
> > if (mdesc->reserve)
> > mdesc->reserve();
> >
> > - early_init_fdt_reserve_self();
> > early_init_fdt_scan_reserved_mem();
> >
> > /* reserve memory for DMA contiguous allocations */
> > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
> > index 0665a0dbd040..a7231d151c63 100644
> > --- a/arch/arm/mm/mmu.c
> > +++ b/arch/arm/mm/mmu.c
> > @@ -40,6 +40,8 @@
> > #include "mm.h"
> > #include "tcm.h"
> >
> > +extern unsigned long __atags_pointer;
> > +
> > /*
> > * empty_zero_page is a special page that is used for
> > * zero-initialized data and COW.
> > @@ -947,7 +949,7 @@ static void __init create_mapping(struct map_desc *md)
> > return;
> > }
> >
> > - if ((md->type == MT_DEVICE || md->type == MT_ROM) &&
> > + if (md->type == MT_DEVICE &&
> > md->virtual >= PAGE_OFFSET && md->virtual < FIXADDR_START &&
> > (md->virtual < VMALLOC_START || md->virtual >= VMALLOC_END)) {
> > pr_warn("BUG: mapping for 0x%08llx at 0x%08lx out of vmalloc space\n",
> > @@ -1343,6 +1345,15 @@ static void __init devicemaps_init(const struct machine_desc *mdesc)
> > for (addr = VMALLOC_START; addr < (FIXADDR_TOP & PMD_MASK); addr += PMD_SIZE)
> > pmd_clear(pmd_off_k(addr));
> >
> > + if (__atags_pointer) {
> > + /* create a read-only mapping of the device tree */
> > + map.pfn = __phys_to_pfn(__atags_pointer & SECTION_MASK);
> > + map.virtual = FDT_FIXED_BASE;
> > + map.length = FDT_FIXED_SIZE;
> > + map.type = MT_ROM;
> > + create_mapping(&map);
> > + }
> > +
> > /*
> > * Map the kernel if it is XIP.
> > * It is always first in the modulearea.
> > @@ -1503,8 +1514,7 @@ static void __init map_lowmem(void)
> > }
> >
> > #ifdef CONFIG_ARM_PV_FIXUP
> > -extern void *atags_vaddr;
> > -typedef void pgtables_remap(long long offset, unsigned long pgd, void *bdata);
> > +typedef void pgtables_remap(long long offset, unsigned long pgd);
> > pgtables_remap lpae_pgtables_remap_asm;
> >
> > /*
> > @@ -1517,7 +1527,6 @@ static void __init early_paging_init(const struct machine_desc *mdesc)
> > unsigned long pa_pgd;
> > unsigned int cr, ttbcr;
> > long long offset;
> > - void *boot_data;
> >
> > if (!mdesc->pv_fixup)
> > return;
> > @@ -1534,7 +1543,6 @@ static void __init early_paging_init(const struct machine_desc *mdesc)
> > */
> > lpae_pgtables_remap = (pgtables_remap *)(unsigned long)__pa(lpae_pgtables_remap_asm);
> > pa_pgd = __pa(swapper_pg_dir);
> > - boot_data = atags_vaddr;
> > barrier();
> >
> > pr_info("Switching physical address space to 0x%08llx\n",
> > @@ -1570,7 +1578,7 @@ static void __init early_paging_init(const struct machine_desc *mdesc)
> > * needs to be assembly. It's fairly simple, as we're using the
> > * temporary tables setup by the initial assembly code.
> > */
> > - lpae_pgtables_remap(offset, pa_pgd, boot_data);
> > + lpae_pgtables_remap(offset, pa_pgd);
> >
> > /* Re-enable the caches and cacheable TLB walks */
> > asm volatile("mcr p15, 0, %0, c2, c0, 2" : : "r" (ttbcr));
> > diff --git a/arch/arm/mm/pv-fixup-asm.S b/arch/arm/mm/pv-fixup-asm.S
> > index 8eade0416739..5c5e1952000a 100644
> > --- a/arch/arm/mm/pv-fixup-asm.S
> > +++ b/arch/arm/mm/pv-fixup-asm.S
> > @@ -39,8 +39,8 @@ ENTRY(lpae_pgtables_remap_asm)
> >
> > /* Update level 2 entries for the boot data */
> > add r7, r2, #0x1000
> > - add r7, r7, r3, lsr #SECTION_SHIFT - L2_ORDER
> > - bic r7, r7, #(1 << L2_ORDER) - 1
> > + movw r3, #FDT_FIXED_BASE >> (SECTION_SHIFT - L2_ORDER)
> > + add r7, r7, r3
> > ldrd r4, r5, [r7]
> > adds r4, r4, r0
> > adc r5, r5, r1
>
> Best regards
> --
> Marek Szyprowski, PhD
> Samsung R&D Institute Poland
>
>
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