[PATCH v2 2/2] ARM: move device tree mapping out of linear region
Ard Biesheuvel
ardb at kernel.org
Wed Oct 7 04:39:44 EDT 2020
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>
---
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
--
2.17.1
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