On Wed, 28 Oct 2020 at 10:22, Ard Biesheuvel <ardb@xxxxxxxxxx> wrote:
>
> On Wed, 28 Oct 2020 at 10:19, Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> 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@xxxxxxxxxx>
> > > Reviewed-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> > > Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> >
> > 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.
> >
>
> Thanks for the report. I will have a look later today.
>
> Do these platforms happen to have any static device mappings that may
> collide with this mapping of the FDT? Also, could this be related to
> device drivers making changes in memory to the FDT image? Because the
> permanent mapping of the FDT is read-only now.
>
IOW, does using MT_MEMORY_RW instead of MT_ROM for the mapping make a
difference?
>
>
> > > ---
> > > 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
> >
