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 <CAAhSdy1h+Akz-esWVG2oeLuhjDedcJyvRntV5LuaK8LhirD=Sw@mail.gmail.com> <a10129d7-33e4-ba05-7c50-3852ba2f1993@ghiti.fr>
In-Reply-To: <a10129d7-33e4-ba05-7c50-3852ba2f1993@ghiti.fr>
From:   Anup Patel <anup@brainfault.org>
Date:   Wed, 6 Jan 2021 12:14:50 +0530
Message-ID: <CAAhSdy0ecu=FeNdu+g8+Q8H1KeTvC_fNprH3EGL-nn8u4yZVaQ@mail.gmail.com>
Subject: Re: [RFC PATCH 01/12] riscv: Move kernel mapping outside of linear mapping
To:     Alex 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 Wed, Jan 6, 2021 at 12:06 PM Alex Ghiti <alex@ghiti.fr> wrote:
>
> Hi Anup,
>
> Le 1/5/21 =C3=A0 6:40 AM, Anup Patel a =C3=A9crit :
> > 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 ba=
se
> >> address will be different from PAGE_OFFSET and since in the linear map=
ping,
> >> two different virtual addresses cannot point to the same physical addr=
ess,
> >> 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 t=
hen
> >> BPF and modules are also pushed to the same range since they have to l=
ie
> >> close to the kernel inside a 2GB window.
> >>
> >> Note then that KASLR implementation will simply have to move the kerne=
l in
> >> this 2GB range and modify BPF/modules regions accordingly.
> >>
> >> In addition, by moving the kernel to the end of the address space, bot=
h
> >> 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
> >>   {
> >> -       . =3D PAGE_OFFSET;
> >> +       . =3D KERNEL_LINK_ADDR;
> >>
> >>          .payload : {
> >>                  *(.payload)
> >> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/pa=
ge.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_of=
fset)
> >> +#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 sp=
ace
> >> + */
> >> +#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)
> >
>
> I think the patch is correct: worst-case, we want the first address of
> the module area to be able to access the last address of the kernel, so
> we must use _end and not _start to guarantee that the difference between
> those 2 addresses is not greater than 2GB.

Makes sense. Please add more detailed comment instead of single-line commen=
t.

>
> >>
> >>   /*
> >>    * 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/vmlin=
ux.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 =3D KERNEL_VIRT_ADDR;
> >> +EXPORT_SYMBOL(kernel_virt_addr);
> >> +
> >>   unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
> >>                                                          __page_aligne=
d_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 addr=
ess */
> >>   unsigned long va_pa_offset;
> >>   EXPORT_SYMBOL(va_pa_offset);
> >> +/* Offset between kernel mapping virtual address and kernel load addr=
ess */
> >> +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 =3D (va - PAGE_OFFSET) >> PGDIR_SHIFT;
> >> +       pmd_num =3D (va - kernel_virt_addr) >> PGDIR_SHIFT;
> >>          BUG_ON(pmd_num >=3D 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 shoul=
d not use absolute addressing."
> >>   #endif
> >>
> >> +static uintptr_t load_pa, load_sz;
> >> +
> >> +static void __init create_kernel_page_table(pgd_t *pgdir, uintptr_t m=
ap_size)
> >> +{
> >> +       uintptr_t va, end_va;
> >> +
> >> +       end_va =3D kernel_virt_addr + load_sz;
> >> +       for (va =3D kernel_virt_addr; va < end_va; va +=3D 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 =3D (uintptr_t)(&_start);
> >> -       uintptr_t load_sz =3D (uintptr_t)(&_end) - load_pa;
> >> -       uintptr_t map_size =3D best_map_size(load_pa, MAX_EARLY_MAPPIN=
G_SIZE);
> >> +       uintptr_t pa;
> >> +       uintptr_t map_size;
> >>   #ifndef __PAGETABLE_PMD_FOLDED
> >>          pmd_t fix_bmap_spmd, fix_bmap_epmd;
> >>   #endif
> >>
> >> +       load_pa =3D (uintptr_t)(&_start);
> >> +       load_sz =3D (uintptr_t)(&_end) - load_pa;
> >> +       map_size =3D best_map_size(load_pa, MAX_EARLY_MAPPING_SIZE);
> >> +
> >>          va_pa_offset =3D PAGE_OFFSET - load_pa;
> >> +       va_kernel_pa_offset =3D kernel_virt_addr - load_pa;
> >> +
> >>          pfn_base =3D 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_TABL=
E);
> >>          /* 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, PAG=
E_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 =3D PAGE_OFFSET + load_sz;
> >> -       for (va =3D PAGE_OFFSET; va < end_va; va +=3D 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 =3D { 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 >=3D end)
> >>                          break;
> >> @@ -577,10 +598,22 @@ static void __init setup_vm_final(void)
> >>                  for (pa =3D start; pa < end; pa +=3D map_size) {
> >>                          va =3D (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 =3D (void *)kernel_virt_addr;
> >> +       vm_kernel.phys_addr =3D load_pa;
> >> +       vm_kernel.size =3D (load_sz + PMD_SIZE - 1) & ~(PMD_SIZE - 1);
> >> +       vm_kernel.flags =3D VM_MAP | VM_NO_GUARD;
> >> +       vm_kernel.caller =3D __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 =3D (unsigned long)PAGE_OFFSET;
> >> +       unsigned long kernel_start =3D (unsigned long)kernel_virt_addr=
;
> >>          unsigned long kernel_end =3D (unsigned long)_end;
> >>
> >>          /*
> >> --
> >> 2.20.1
> >>
> >
> > Apart from the minor comment above, this looks good to me.
> >
> > Reviewed-by: Anup Patel <anup@brainfault.org>
>
> Thanks for your time Anup,
>
> >
> > Regards,
> > Anup
> >
>
> Alex

Regards,
Anup