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In-Reply-To: <20210104195840.1593-2-alex@ghiti.fr>
From:   Anup Patel <anup@brainfault.org>
Date:   Tue, 5 Jan 2021 17:10:01 +0530
Message-ID: <CAAhSdy1h+Akz-esWVG2oeLuhjDedcJyvRntV5LuaK8LhirD=Sw@mail.gmail.com>
Subject: Re: [RFC PATCH 01/12] riscv: Move kernel mapping outside of linear mapping
To:     Alexandre Ghiti <alex@ghiti.fr>
Cc:     Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Zong Li <zong.li@sifive.com>, Christoph Hellwig <hch@lst.de>,
        Ard Biesheuvel <ardb@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        linux-efi <linux-efi@vger.kernel.org>,
        linux-arch@vger.kernel.org,
        linux-riscv <linux-riscv@lists.infradead.org>,
        "linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>
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On Tue, Jan 5, 2021 at 1:29 AM Alexandre Ghiti <alex@ghiti.fr> 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@arndb.de>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> ---
>  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)

>
>  /*
>   * 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@brainfault.org>

Regards,
Anup