Re: [RFC PATCH 01/12] riscv: Move kernel mapping outside of linear mapping
From: Alex Ghiti
Date: Wed Jan 06 2021 - 01:37:23 EST
Hi Anup,
Le 1/5/21 à 6:40 AM, Anup Patel a écrit :
On Tue, Jan 5, 2021 at 1:29 AM Alexandre Ghiti <alex@xxxxxxxx> wrote:
This is a preparatory patch for relocatable kernel and sv48 support.
The kernel used to be linked at PAGE_OFFSET address therefore we could use
the linear mapping for the kernel mapping. But the relocated kernel base
address will be different from PAGE_OFFSET and since in the linear mapping,
two different virtual addresses cannot point to the same physical address,
the kernel mapping needs to lie outside the linear mapping so that we don't
have to copy it at the same physical offset.
The kernel mapping is moved to the last 2GB of the address space and then
BPF and modules are also pushed to the same range since they have to lie
close to the kernel inside a 2GB window.
Note then that KASLR implementation will simply have to move the kernel in
this 2GB range and modify BPF/modules regions accordingly.
In addition, by moving the kernel to the end of the address space, both
sv39 and sv48 kernels will be exactly the same without needing to be
relocated at runtime.
Awesome ! This is a good approach with no performance impact.
Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
---
arch/riscv/boot/loader.lds.S | 3 +-
arch/riscv/include/asm/page.h | 10 ++++-
arch/riscv/include/asm/pgtable.h | 39 +++++++++++++------
arch/riscv/kernel/head.S | 3 +-
arch/riscv/kernel/module.c | 4 +-
arch/riscv/kernel/vmlinux.lds.S | 3 +-
arch/riscv/mm/init.c | 65 ++++++++++++++++++++++++--------
arch/riscv/mm/physaddr.c | 2 +-
8 files changed, 94 insertions(+), 35 deletions(-)
diff --git a/arch/riscv/boot/loader.lds.S b/arch/riscv/boot/loader.lds.S
index 47a5003c2e28..62d94696a19c 100644
--- a/arch/riscv/boot/loader.lds.S
+++ b/arch/riscv/boot/loader.lds.S
@@ -1,13 +1,14 @@
/* SPDX-License-Identifier: GPL-2.0 */
#include <asm/page.h>
+#include <asm/pgtable.h>
OUTPUT_ARCH(riscv)
ENTRY(_start)
SECTIONS
{
- . = PAGE_OFFSET;
+ . = KERNEL_LINK_ADDR;
.payload : {
*(.payload)
diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
index 2d50f76efe48..98188e315e8d 100644
--- a/arch/riscv/include/asm/page.h
+++ b/arch/riscv/include/asm/page.h
@@ -90,18 +90,26 @@ typedef struct page *pgtable_t;
#ifdef CONFIG_MMU
extern unsigned long va_pa_offset;
+extern unsigned long va_kernel_pa_offset;
extern unsigned long pfn_base;
#define ARCH_PFN_OFFSET (pfn_base)
#else
#define va_pa_offset 0
+#define va_kernel_pa_offset 0
#define ARCH_PFN_OFFSET (PAGE_OFFSET >> PAGE_SHIFT)
#endif /* CONFIG_MMU */
extern unsigned long max_low_pfn;
extern unsigned long min_low_pfn;
+extern unsigned long kernel_virt_addr;
#define __pa_to_va_nodebug(x) ((void *)((unsigned long) (x) + va_pa_offset))
-#define __va_to_pa_nodebug(x) ((unsigned long)(x) - va_pa_offset)
+#define linear_mapping_va_to_pa(x) ((unsigned long)(x) - va_pa_offset)
+#define kernel_mapping_va_to_pa(x) \
+ ((unsigned long)(x) - va_kernel_pa_offset)
+#define __va_to_pa_nodebug(x) \
+ (((x) < KERNEL_LINK_ADDR) ? \
+ linear_mapping_va_to_pa(x) : kernel_mapping_va_to_pa(x))
#ifdef CONFIG_DEBUG_VIRTUAL
extern phys_addr_t __virt_to_phys(unsigned long x);
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 183f1f4b2ae6..102b728ca146 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -11,23 +11,32 @@
#include <asm/pgtable-bits.h>
-#ifndef __ASSEMBLY__
-
-/* Page Upper Directory not used in RISC-V */
-#include <asm-generic/pgtable-nopud.h>
-#include <asm/page.h>
-#include <asm/tlbflush.h>
-#include <linux/mm_types.h>
+#ifndef CONFIG_MMU
+#define KERNEL_VIRT_ADDR PAGE_OFFSET
+#define KERNEL_LINK_ADDR PAGE_OFFSET
+#else
-#ifdef CONFIG_MMU
+#define ADDRESS_SPACE_END (UL(-1))
+/*
+ * Leave 2GB for kernel, modules and BPF at the end of the address space
+ */
+#define KERNEL_VIRT_ADDR (ADDRESS_SPACE_END - SZ_2G + 1)
+#define KERNEL_LINK_ADDR KERNEL_VIRT_ADDR
#define VMALLOC_SIZE (KERN_VIRT_SIZE >> 1)
#define VMALLOC_END (PAGE_OFFSET - 1)
#define VMALLOC_START (PAGE_OFFSET - VMALLOC_SIZE)
+/* KASLR should leave at least 128MB for BPF after the kernel */
#define BPF_JIT_REGION_SIZE (SZ_128M)
-#define BPF_JIT_REGION_START (PAGE_OFFSET - BPF_JIT_REGION_SIZE)
-#define BPF_JIT_REGION_END (VMALLOC_END)
+#define BPF_JIT_REGION_START PFN_ALIGN((unsigned long)&_end)
+#define BPF_JIT_REGION_END (BPF_JIT_REGION_START + BPF_JIT_REGION_SIZE)
+
+/* Modules always live before the kernel */
+#ifdef CONFIG_64BIT
+#define VMALLOC_MODULE_START (PFN_ALIGN((unsigned long)&_end) - SZ_2G)
+#define VMALLOC_MODULE_END (PFN_ALIGN((unsigned long)&_start))
+#endif
This does not look right or I am missing something.
I think the VMALLOC_MODULE_START should be:
#define VMALLOC_MODULE_START (PFN_ALIGN((unsigned long)&_start) - SZ_2G)
I think the patch is correct: worst-case, we want the first address of
the module area to be able to access the last address of the kernel, so
we must use _end and not _start to guarantee that the difference between
those 2 addresses is not greater than 2GB.
/*
* Roughly size the vmemmap space to be large enough to fit enough
@@ -57,9 +66,16 @@
#define FIXADDR_SIZE PGDIR_SIZE
#endif
#define FIXADDR_START (FIXADDR_TOP - FIXADDR_SIZE)
-
#endif
+#ifndef __ASSEMBLY__
+
+/* Page Upper Directory not used in RISC-V */
+#include <asm-generic/pgtable-nopud.h>
+#include <asm/page.h>
+#include <asm/tlbflush.h>
+#include <linux/mm_types.h>
+
#ifdef CONFIG_64BIT
#include <asm/pgtable-64.h>
#else
@@ -467,6 +483,7 @@ static inline void __kernel_map_pages(struct page *page, int numpages, int enabl
#define kern_addr_valid(addr) (1) /* FIXME */
+extern char _start[];
extern void *dtb_early_va;
extern uintptr_t dtb_early_pa;
void setup_bootmem(void);
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index 7e849797c9c3..66f40c49bf68 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -69,7 +69,8 @@ pe_head_start:
#ifdef CONFIG_MMU
relocate:
/* Relocate return address */
- li a1, PAGE_OFFSET
+ la a1, kernel_virt_addr
+ REG_L a1, 0(a1)
la a2, _start
sub a1, a1, a2
add ra, ra, a1
diff --git a/arch/riscv/kernel/module.c b/arch/riscv/kernel/module.c
index 104fba889cf7..75a0b9541266 100644
--- a/arch/riscv/kernel/module.c
+++ b/arch/riscv/kernel/module.c
@@ -408,12 +408,10 @@ int apply_relocate_add(Elf_Shdr *sechdrs, const char *strtab,
}
#if defined(CONFIG_MMU) && defined(CONFIG_64BIT)
-#define VMALLOC_MODULE_START \
- max(PFN_ALIGN((unsigned long)&_end - SZ_2G), VMALLOC_START)
void *module_alloc(unsigned long size)
{
return __vmalloc_node_range(size, 1, VMALLOC_MODULE_START,
- VMALLOC_END, GFP_KERNEL,
+ VMALLOC_MODULE_END, GFP_KERNEL,
PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
__builtin_return_address(0));
}
diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 3ffbd6cbdb86..c21dc46f41be 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -4,7 +4,8 @@
* Copyright (C) 2017 SiFive
*/
-#define LOAD_OFFSET PAGE_OFFSET
+#include <asm/pgtable.h>
+#define LOAD_OFFSET KERNEL_LINK_ADDR
#include <asm/vmlinux.lds.h>
#include <asm/page.h>
#include <asm/cache.h>
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 8e577f14f120..9d06ff0e015a 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -23,6 +23,9 @@
#include "../kernel/head.h"
+unsigned long kernel_virt_addr = KERNEL_VIRT_ADDR;
+EXPORT_SYMBOL(kernel_virt_addr);
+
unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
__page_aligned_bss;
EXPORT_SYMBOL(empty_zero_page);
@@ -201,8 +204,12 @@ void __init setup_bootmem(void)
#ifdef CONFIG_MMU
static struct pt_alloc_ops pt_ops;
+/* Offset between linear mapping virtual address and kernel load address */
unsigned long va_pa_offset;
EXPORT_SYMBOL(va_pa_offset);
+/* Offset between kernel mapping virtual address and kernel load address */
+unsigned long va_kernel_pa_offset;
+EXPORT_SYMBOL(va_kernel_pa_offset);
unsigned long pfn_base;
EXPORT_SYMBOL(pfn_base);
@@ -316,7 +323,7 @@ static phys_addr_t __init alloc_pmd_early(uintptr_t va)
{
uintptr_t pmd_num;
- pmd_num = (va - PAGE_OFFSET) >> PGDIR_SHIFT;
+ pmd_num = (va - kernel_virt_addr) >> PGDIR_SHIFT;
BUG_ON(pmd_num >= NUM_EARLY_PMDS);
return (uintptr_t)&early_pmd[pmd_num * PTRS_PER_PMD];
}
@@ -431,17 +438,34 @@ static uintptr_t __init best_map_size(phys_addr_t base, phys_addr_t size)
#error "setup_vm() is called from head.S before relocate so it should not use absolute addressing."
#endif
+static uintptr_t load_pa, load_sz;
+
+static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t map_size)
+{
+ uintptr_t va, end_va;
+
+ end_va = kernel_virt_addr + load_sz;
+ for (va = kernel_virt_addr; va < end_va; va += map_size)
+ create_pgd_mapping(pgdir, va,
+ load_pa + (va - kernel_virt_addr),
+ map_size, PAGE_KERNEL_EXEC);
+}
+
asmlinkage void __init setup_vm(uintptr_t dtb_pa)
{
- uintptr_t va, pa, end_va;
- uintptr_t load_pa = (uintptr_t)(&_start);
- uintptr_t load_sz = (uintptr_t)(&_end) - load_pa;
- uintptr_t map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
+ uintptr_t pa;
+ uintptr_t map_size;
#ifndef __PAGETABLE_PMD_FOLDED
pmd_t fix_bmap_spmd, fix_bmap_epmd;
#endif
+ load_pa = (uintptr_t)(&_start);
+ load_sz = (uintptr_t)(&_end) - load_pa;
+ map_size = best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
+
va_pa_offset = PAGE_OFFSET - load_pa;
+ va_kernel_pa_offset = kernel_virt_addr - load_pa;
+
pfn_base = PFN_DOWN(load_pa);
/*
@@ -470,26 +494,22 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
create_pmd_mapping(fixmap_pmd, FIXADDR_START,
(uintptr_t)fixmap_pte, PMD_SIZE, PAGE_TABLE);
/* Setup trampoline PGD and PMD */
- create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
+ create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
(uintptr_t)trampoline_pmd, PGDIR_SIZE, PAGE_TABLE);
- create_pmd_mapping(trampoline_pmd, PAGE_OFFSET,
+ create_pmd_mapping(trampoline_pmd, kernel_virt_addr,
load_pa, PMD_SIZE, PAGE_KERNEL_EXEC);
#else
/* Setup trampoline PGD */
- create_pgd_mapping(trampoline_pg_dir, PAGE_OFFSET,
+ create_pgd_mapping(trampoline_pg_dir, kernel_virt_addr,
load_pa, PGDIR_SIZE, PAGE_KERNEL_EXEC);
#endif
/*
- * Setup early PGD covering entire kernel which will allows
+ * Setup early PGD covering entire kernel which will allow
* us to reach paging_init(). We map all memory banks later
* in setup_vm_final() below.
*/
- end_va = PAGE_OFFSET + load_sz;
- for (va = PAGE_OFFSET; va < end_va; va += map_size)
- create_pgd_mapping(early_pg_dir, va,
- load_pa + (va - PAGE_OFFSET),
- map_size, PAGE_KERNEL_EXEC);
+ create_kernel_page_table(early_pg_dir, map_size);
#ifndef __PAGETABLE_PMD_FOLDED
/* Setup early PMD for DTB */
@@ -549,6 +569,7 @@ static void __init setup_vm_final(void)
uintptr_t va, map_size;
phys_addr_t pa, start, end;
u64 i;
+ static struct vm_struct vm_kernel = { 0 };
/**
* MMU is enabled at this point. But page table setup is not complete yet.
@@ -565,7 +586,7 @@ static void __init setup_vm_final(void)
__pa_symbol(fixmap_pgd_next),
PGDIR_SIZE, PAGE_TABLE);
- /* Map all memory banks */
+ /* Map all memory banks in the linear mapping */
for_each_mem_range(i, &start, &end) {
if (start >= end)
break;
@@ -577,10 +598,22 @@ static void __init setup_vm_final(void)
for (pa = start; pa < end; pa += map_size) {
va = (uintptr_t)__va(pa);
create_pgd_mapping(swapper_pg_dir, va, pa,
- map_size, PAGE_KERNEL_EXEC);
+ map_size, PAGE_KERNEL);
}
}
+ /* Map the kernel */
+ create_kernel_page_table(swapper_pg_dir, PMD_SIZE);
+
+ /* Reserve the vmalloc area occupied by the kernel */
+ vm_kernel.addr = (void *)kernel_virt_addr;
+ vm_kernel.phys_addr = load_pa;
+ vm_kernel.size = (load_sz + PMD_SIZE - 1) & ~(PMD_SIZE - 1);
+ vm_kernel.flags = VM_MAP | VM_NO_GUARD;
+ vm_kernel.caller = __builtin_return_address(0);
+
+ vm_area_add_early(&vm_kernel);
+
/* Clear fixmap PTE and PMD mappings */
clear_fixmap(FIX_PTE);
clear_fixmap(FIX_PMD);
diff --git a/arch/riscv/mm/physaddr.c b/arch/riscv/mm/physaddr.c
index e8e4dcd39fed..35703d5ef5fd 100644
--- a/arch/riscv/mm/physaddr.c
+++ b/arch/riscv/mm/physaddr.c
@@ -23,7 +23,7 @@ EXPORT_SYMBOL(__virt_to_phys);
phys_addr_t __phys_addr_symbol(unsigned long x)
{
- unsigned long kernel_start = (unsigned long)PAGE_OFFSET;
+ unsigned long kernel_start = (unsigned long)kernel_virt_addr;
unsigned long kernel_end = (unsigned long)_end;
/*
--
2.20.1
Apart from the minor comment above, this looks good to me.
Reviewed-by: Anup Patel <anup@xxxxxxxxxxxxxx>
Thanks for your time Anup,
Regards,
Anup
Alex