Re: [PATCH v3 1/3] riscv: Move kernel mapping to vmalloc zone

[Alex Ghiti <alex@ghiti.fr>]

Le 5/27/20 à 2:05 AM, Zong Li a écrit :
> On Wed, May 27, 2020 at 1:06 AM Alex Ghiti <alex@ghiti.fr> wrote:
>> Hi Zong,
>>
>> Le 5/26/20 à 5:43 AM, Zong Li a écrit :
>>> On Sun, May 24, 2020 at 4:54 PM Alexandre Ghiti <alex@ghiti.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@ghiti.fr>
>>>> ---
>>>>    arch/riscv/boot/loader.lds.S     |  3 +-
>>>>    arch/riscv/include/asm/page.h    | 10 +++++-
>>>>    arch/riscv/include/asm/pgtable.h | 37 +++++++++++++-------
>>>>    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, 87 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..25213cfaf680 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   (kernel_virt_addr)
>>>> +#define BPF_JIT_REGION_END     (kernel_virt_addr + BPF_JIT_REGION_SIZE)
>>> It seems to have a potential risk here, the region of bpf is
>>> overlapping with kernel mapping, so if kernel size is bigger than
>>> 128MB, bpf region would be occupied and run out by kernel mapping.
> Is there the risk as I mentioned?


Sorry I forgot to answer this one: I was confident that 128MB was large 
enough for kernel
and BPF. But I see no reason to leave this risk so I'll change 
kernel_virt_addr for _end so
BPF will have its 128MB reserved.

Thanks !

Alex


>
>>>> +
>>>> +#ifdef CONFIG_64BIT
>>>> +#define VMALLOC_MODULE_START   BPF_JIT_REGION_END
>>>> +#define VMALLOC_MODULE_END     VMALLOC_END
>>>> +#endif
>>>>
>>> Although kernel_virt_addr is a fixed address now, I think it could be
>>> changed for the purpose of relocatable or KASLR, so if
>>> kernel_virt_addr is moved to far from VMALLOC_END than 2G, the region
>>> of module would be too big.
>>
>> Yes you're right, that's wrong to allow modules to lie outside
>> the 2G window, thanks for noticing.
>>
>>
>>> In addition, the region of module could be
>>> +-2G around the kernel, so we don't be limited in one direction as
>>> before. It seems to me that the region of the module could be decided
>>> at runtime, for example, VMALLOC_MODULE_START is "&_end - 2G" and
>>> VMLLOC_MODULE_END is "&_start + 2G".
>>
>> I had tried that, but as we need to make sure BPF region is different
>> from the module's
>> that makes the macro definitions really cumbersome. I'll give a try
>> again anyway. And
>> I tried to use _end and _start here but it failed, I have to debug this.
>>
>>
>>>    I'm not sure whether the size of
>>> region of bpf has to be 128MB for some particular reason, if not,
>>> maybe the region of bpf could be the same with module to avoid being
>>> run out by module.
>>
>> On the contrary, BPF region must not be the same as module's since in
>> that case,
>> modules could take all the space and make BPF fail.
> ok, I got it. Thanks for the explaining.
>
>
>>
>> Thanks for your review Zong,
>>
>>
>> Alex
>>
>>
>>>>    /*
>>>>     * 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
>>>> 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 27a334106708..17f108baec4f 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;
>>>> +
>>>> +void 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) & ~(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
>>>>