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

From: Zong Li
Date: Wed May 27 2020 - 02:05:57 EST

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In reply to: Alex Ghiti: "Re: [PATCH v3 1/3] riscv: Move kernel mapping to vmalloc zone"
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On Wed, May 27, 2020 at 1:06 AM Alex Ghiti <alex@xxxxxxxx> wrote:
>
> Hi Zong,
>
> Le 5/26/20 Ã 5:43 AM, Zong Li a Ãcrit :
> > On Sun, May 24, 2020 at 4:54 PM Alexandre Ghiti <alex@xxxxxxxx> 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@xxxxxxxx>
> >> ---
> >> 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?

> >
> >> +
> >> +#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
> >>

Next message: Jianyong Wu: "RE: [RFC PATCH v12 07/11] psci: Add hypercall service for kvm ptp."
Previous message: Jason Wang: "[PATCH] vdpa: fix typos in the comments for __vdpa_alloc_device()"
In reply to: Alex Ghiti: "Re: [PATCH v3 1/3] riscv: Move kernel mapping to vmalloc zone"
Next in thread: Alex Ghiti: "Re: [PATCH v3 1/3] riscv: Move kernel mapping to vmalloc zone"
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