[PATCH v5 1/4] riscv: Move kernel mapping to vmalloc zone
Alex Ghiti
alex at ghiti.fr
Tue Jul 21 14:36:10 EDT 2020
Let's try to make progress here: I add linux-mm in CC to get feedback on
this patch as it blocks sv48 support too.
Alex
Le 7/9/20 à 7:11 AM, Alex Ghiti a écrit :
> Hi Palmer,
>
> Le 7/9/20 à 1:05 AM, Palmer Dabbelt a écrit :
>> On Sun, 07 Jun 2020 00:59:46 PDT (-0700), alex at 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.
>>
>> I know it's been a while, but I keep opening this up to review it and
>> just
>> can't get over how ugly it is to put the kernel's linear map in the
>> vmalloc
>> region.
>>
>> I guess I don't understand why this is necessary at all.
>> Specifically: why
>> can't we just relocate the kernel within the linear map? That would
>> let the
>> bootloader put the kernel wherever it wants, modulo the physical
>> memory size we
>> support. We'd need to handle the regions that are coupled to the
>> kernel's
>> execution address, but we could just put them in an explicit memory
>> region
>> which is what we should probably be doing anyway.
>
> Virtual relocation in the linear mapping requires to move the kernel
> physically too. Zong implemented this physical move in its KASLR RFC
> patchset, which is cumbersome since finding an available physical spot
> is harder than just selecting a virtual range in the vmalloc range.
>
> In addition, having the kernel mapping in the linear mapping prevents
> the use of hugepage for the linear mapping resulting in performance loss
> (at least for the GB that encompasses the kernel).
>
> Why do you find this "ugly" ? The vmalloc region is just a bunch of
> available virtual addresses to whatever purpose we want, and as noted by
> Zong, arm64 uses the same scheme.
>
>>
>>> 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.
>>
>> Well, that's not enough to make sure this doesn't happen -- it's just
>> enough to
>> make sure it doesn't happen very quickily. That's the same boat we're
>> already
>> in, though, so it's not like it's worse.
>
> Indeed, that's not worse, I haven't found a way to reserve vmalloc area
> without actually allocating it.
>
>>
>>> Signed-off-by: Alexandre Ghiti <alex at ghiti.fr>
>>> Reviewed-by: Zong Li <zong.li at sifive.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
>>
>> At a bare minimum this is going to make a mess of the 32-bit port, as
>> non-relocatable kernels are now going to get linked at 1GiB which is
>> where user
>> code is supposed to live. That's an easy fix, though, as the 32-bit
>> stuff
>> doesn't need any module address restrictions.
>
> Indeed, I will take a look at that.
>
>>
>>> #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)
>>> +
>>> +#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;
>>>
>>> /*
>
> Alex
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