Messages in this thread | | | Subject | Re: [PATCH v5 1/4] riscv: Move kernel mapping to vmalloc zone | From | Alex Ghiti <> | Date | Tue, 21 Jul 2020 14:36:10 -0400 |
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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@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@ghiti.fr> >>> Reviewed-by: Zong Li <zong.li@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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