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Message-ID: <CAOnJCULMXX1OyLsFZMWj2tMftsCY1rqmN1QxYH+Y7Z-3a5Ap7g@mail.gmail.com>
Date: Thu, 11 Jun 2020 14:34:22 -0700
From: Atish Patra <atishp@...shpatra.org>
To: Alexandre Ghiti <alex@...ti.fr>
Cc: Michael Ellerman <mpe@...erman.id.au>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Anup Patel <Anup.Patel@....com>,
Atish Patra <Atish.Patra@....com>,
Zong Li <zong.li@...ive.com>,
"linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
linuxppc-dev@...ts.ozlabs.org,
linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH v5 1/4] riscv: Move kernel mapping to vmalloc zone
On Sun, Jun 7, 2020 at 1:01 AM Alexandre Ghiti <alex@...ti.fr> wrote:
>
> This is a preparatory patch for relocatable kernel.
>
> The kernel used to be linked at PAGE_OFFSET address and used to be loaded
> physically at the beginning of the main memory. 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.
>
> In addition, because modules and BPF must be close to the kernel (inside
> +-2GB window), the kernel is placed at the end of the vmalloc zone minus
> 2GB, which leaves room for modules and BPF. The kernel could not be
> placed at the beginning of the vmalloc zone since other vmalloc
> allocations from the kernel could get all the +-2GB window around the
> kernel which would prevent new modules and BPF programs to be loaded.
>
> Signed-off-by: Alexandre Ghiti <alex@...ti.fr>
> Reviewed-by: Zong Li <zong.li@...ive.com>
> ---
> arch/riscv/boot/loader.lds.S | 3 +-
> arch/riscv/include/asm/page.h | 10 +++++-
> arch/riscv/include/asm/pgtable.h | 38 ++++++++++++++-------
> arch/riscv/kernel/head.S | 3 +-
> arch/riscv/kernel/module.c | 4 +--
> arch/riscv/kernel/vmlinux.lds.S | 3 +-
> arch/riscv/mm/init.c | 58 +++++++++++++++++++++++++-------
> arch/riscv/mm/physaddr.c | 2 +-
> 8 files changed, 88 insertions(+), 33 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..48bb09b6a9b7 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) >= PAGE_OFFSET) ? \
> + 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 35b60035b6b0..94ef3b49dfb6 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -11,23 +11,29 @@
>
> #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>
> -
> -#ifdef CONFIG_MMU
> +#ifndef CONFIG_MMU
> +#define KERNEL_VIRT_ADDR PAGE_OFFSET
> +#define KERNEL_LINK_ADDR PAGE_OFFSET
> +#else
> +/*
> + * Leave 2GB for modules and BPF that must lie within a 2GB range around
> + * the kernel.
> + */
> +#define KERNEL_VIRT_ADDR (VMALLOC_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)
>
> #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)
> +
As these mappings have changed a few times in recent months including
this one, I think it would be
better to have virtual memory layout documentation in RISC-V similar
to other architectures.
If you can include the page table layout for 3/4 level page tables in
the same document, that would be really helpful.
> +#ifdef CONFIG_64BIT
> +#define VMALLOC_MODULE_START BPF_JIT_REGION_END
> +#define VMALLOC_MODULE_END (((unsigned long)&_start & PAGE_MASK) + SZ_2G)
> +#endif
>
> /*
> * Roughly size the vmemmap space to be large enough to fit enough
> @@ -57,9 +63,16 @@
> #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
> @@ -483,6 +496,7 @@ 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;
> void setup_bootmem(void);
> void paging_init(void);
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 98a406474e7d..8f5bb7731327 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -49,7 +49,8 @@ ENTRY(_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 8bbe5dbe1341..1a8fbe05accf 100644
> --- a/arch/riscv/kernel/module.c
> +++ b/arch/riscv/kernel/module.c
> @@ -392,12 +392,10 @@ 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 0339b6bbe11a..a9abde62909f 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 736de6c8739f..71da78914645 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -22,6 +22,9 @@
>
> #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);
> @@ -178,8 +181,12 @@ void __init setup_bootmem(void)
> }
>
> #ifdef CONFIG_MMU
> +/* 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);
>
> @@ -271,7 +278,7 @@ static phys_addr_t __init alloc_pmd(uintptr_t va)
> if (mmu_enabled)
> return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>
> - 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];
> }
> @@ -372,14 +379,30 @@ 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, 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);
>
> + load_pa = (uintptr_t)(&_start);
> + load_sz = (uintptr_t)(&_end) - load_pa;
> +
> va_pa_offset = PAGE_OFFSET - load_pa;
> + va_kernel_pa_offset = kernel_virt_addr - load_pa;
> +
> pfn_base = PFN_DOWN(load_pa);
>
> /*
> @@ -402,26 +425,22 @@ 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);
>
> /* Create fixed mapping for early FDT parsing */
> end_va = __fix_to_virt(FIX_FDT) + FIX_FDT_SIZE;
> @@ -441,6 +460,7 @@ static void __init setup_vm_final(void)
> uintptr_t va, map_size;
> phys_addr_t pa, start, end;
> struct memblock_region *reg;
> + static struct vm_struct vm_kernel = { 0 };
>
> /* Set mmu_enabled flag */
> mmu_enabled = true;
> @@ -467,10 +487,22 @@ 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
>
>
--
Regards,
Atish
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