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References: <20200524091008.25587-1-alex@ghiti.fr> <20200524091008.25587-6-alex@ghiti.fr>
In-Reply-To: <20200524091008.25587-6-alex@ghiti.fr>
From:   Anup Patel <anup@brainfault.org>
Date:   Mon, 25 May 2020 11:40:23 +0530
Message-ID: <CAAhSdy3zbTu4ZOXnx=iJHBkzB2o=xXj6EAB68bhUUW5Hnsu9ng@mail.gmail.com>
Subject: Re: [PATCH 5/8] riscv: Implement sv48 support
To:     Alexandre 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>,
        linux-riscv <linux-riscv@lists.infradead.org>,
        "linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Sun, May 24, 2020 at 2:45 PM Alexandre Ghiti <alex@ghiti.fr> wrote:
>
> By adding a new 4th level of page table, give the possibility to 64bit
> kernel to address 2^48 bytes of virtual address: in practice, that roughly
> offers ~160TB of virtual address space to userspace and allows up to 64TB
> of physical memory.
>
> If the underlying hardware does not support sv48, we will automatically
> fallback to a standard 3-level page table by folding the new PUD level into
> PGDIR level. In order to detect HW capabilities at runtime, we
> use SATP feature that ignores writes with an unsupported mode.
>
> Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
> ---
>  arch/riscv/Kconfig                  |   6 +-
>  arch/riscv/include/asm/csr.h        |   3 +-
>  arch/riscv/include/asm/fixmap.h     |   1 +
>  arch/riscv/include/asm/page.h       |  15 +++
>  arch/riscv/include/asm/pgalloc.h    |  36 +++++++
>  arch/riscv/include/asm/pgtable-64.h |  97 ++++++++++++++++-
>  arch/riscv/include/asm/pgtable.h    |   9 +-
>  arch/riscv/kernel/head.S            |   3 +-
>  arch/riscv/mm/context.c             |   4 +-
>  arch/riscv/mm/init.c                | 159 +++++++++++++++++++++++++---
>  10 files changed, 309 insertions(+), 24 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index e167f16131f4..3f73f60e9732 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -68,6 +68,7 @@ config RISCV
>         select ARCH_HAS_GCOV_PROFILE_ALL
>         select HAVE_COPY_THREAD_TLS
>         select HAVE_ARCH_KASAN if MMU && 64BIT
> +       select RELOCATABLE if 64BIT
>
>  config ARCH_MMAP_RND_BITS_MIN
>         default 18 if 64BIT
> @@ -106,7 +107,7 @@ config PAGE_OFFSET
>         default 0xC0000000 if 32BIT && MAXPHYSMEM_2GB
>         default 0x80000000 if 64BIT && !MMU
>         default 0xffffffff80000000 if 64BIT && MAXPHYSMEM_2GB
> -       default 0xffffffe000000000 if 64BIT && !MAXPHYSMEM_2GB
> +       default 0xffffc00000000000 if 64BIT && !MAXPHYSMEM_2GB
>
>  config ARCH_FLATMEM_ENABLE
>         def_bool y
> @@ -155,8 +156,11 @@ config GENERIC_HWEIGHT
>  config FIX_EARLYCON_MEM
>         def_bool MMU
>
> +# On a 64BIT relocatable kernel, the 4-level page table is at runtime folded
> +# on a 3-level page table when sv48 is not supported.
>  config PGTABLE_LEVELS
>         int
> +       default 4 if 64BIT && RELOCATABLE
>         default 3 if 64BIT
>         default 2
>
> diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
> index cec462e198ce..d41536c3f8d4 100644
> --- a/arch/riscv/include/asm/csr.h
> +++ b/arch/riscv/include/asm/csr.h
> @@ -40,11 +40,10 @@
>  #ifndef CONFIG_64BIT
>  #define SATP_PPN       _AC(0x003FFFFF, UL)
>  #define SATP_MODE_32   _AC(0x80000000, UL)
> -#define SATP_MODE      SATP_MODE_32
>  #else
>  #define SATP_PPN       _AC(0x00000FFFFFFFFFFF, UL)
>  #define SATP_MODE_39   _AC(0x8000000000000000, UL)
> -#define SATP_MODE      SATP_MODE_39
> +#define SATP_MODE_48   _AC(0x9000000000000000, UL)
>  #endif
>
>  /* Exception cause high bit - is an interrupt if set */
> diff --git a/arch/riscv/include/asm/fixmap.h b/arch/riscv/include/asm/fixmap.h
> index 2368d49eb4ef..d891cf9c73c5 100644
> --- a/arch/riscv/include/asm/fixmap.h
> +++ b/arch/riscv/include/asm/fixmap.h
> @@ -27,6 +27,7 @@ enum fixed_addresses {
>         FIX_FDT = FIX_FDT_END + FIX_FDT_SIZE / PAGE_SIZE - 1,
>         FIX_PTE,
>         FIX_PMD,
> +       FIX_PUD,
>         FIX_TEXT_POKE1,
>         FIX_TEXT_POKE0,
>         FIX_EARLYCON_MEM_BASE,
> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
> index 48bb09b6a9b7..5e77fe7f0d6d 100644
> --- a/arch/riscv/include/asm/page.h
> +++ b/arch/riscv/include/asm/page.h
> @@ -31,7 +31,19 @@
>   * When not using MMU this corresponds to the first free page in
>   * physical memory (aligned on a page boundary).
>   */
> +#ifdef CONFIG_RELOCATABLE
> +#define PAGE_OFFSET            __page_offset
> +
> +#ifdef CONFIG_64BIT
> +/*
> + * By default, CONFIG_PAGE_OFFSET value corresponds to SV48 address space so
> + * define the PAGE_OFFSET value for SV39.
> + */
> +#define PAGE_OFFSET_L3         0xffffffe000000000
> +#endif /* CONFIG_64BIT */
> +#else
>  #define PAGE_OFFSET            _AC(CONFIG_PAGE_OFFSET, UL)
> +#endif /* CONFIG_RELOCATABLE */
>
>  #define KERN_VIRT_SIZE (-PAGE_OFFSET)
>
> @@ -102,6 +114,9 @@ extern unsigned long pfn_base;
>  extern unsigned long max_low_pfn;
>  extern unsigned long min_low_pfn;
>  extern unsigned long kernel_virt_addr;
> +#ifdef CONFIG_RELOCATABLE
> +extern unsigned long __page_offset;
> +#endif
>
>  #define __pa_to_va_nodebug(x)  ((void *)((unsigned long) (x) + va_pa_offset))
>  #define linear_mapping_va_to_pa(x)     ((unsigned long)(x) - va_pa_offset)
> diff --git a/arch/riscv/include/asm/pgalloc.h b/arch/riscv/include/asm/pgalloc.h
> index 3f601ee8233f..540eaa5a8658 100644
> --- a/arch/riscv/include/asm/pgalloc.h
> +++ b/arch/riscv/include/asm/pgalloc.h
> @@ -36,6 +36,42 @@ static inline void pud_populate(struct mm_struct *mm, pud_t *pud, pmd_t *pmd)
>
>         set_pud(pud, __pud((pfn << _PAGE_PFN_SHIFT) | _PAGE_TABLE));
>  }
> +
> +static inline void p4d_populate(struct mm_struct *mm, p4d_t *p4d, pud_t *pud)
> +{
> +       if (pgtable_l4_enabled) {
> +               unsigned long pfn = virt_to_pfn(pud);
> +
> +               set_p4d(p4d, __p4d((pfn << _PAGE_PFN_SHIFT) | _PAGE_TABLE));
> +       }
> +}
> +
> +static inline void p4d_populate_safe(struct mm_struct *mm, p4d_t *p4d,
> +                                    pud_t *pud)
> +{
> +       if (pgtable_l4_enabled) {
> +               unsigned long pfn = virt_to_pfn(pud);
> +
> +               set_p4d_safe(p4d,
> +                            __p4d((pfn << _PAGE_PFN_SHIFT) | _PAGE_TABLE));
> +       }
> +}
> +
> +static inline pud_t *pud_alloc_one(struct mm_struct *mm, unsigned long addr)
> +{
> +       if (pgtable_l4_enabled)
> +               return (pud_t *)__get_free_page(
> +                               GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_ZERO);
> +       return NULL;
> +}
> +
> +static inline void pud_free(struct mm_struct *mm, pud_t *pud)
> +{
> +       if (pgtable_l4_enabled)
> +               free_page((unsigned long)pud);
> +}
> +
> +#define __pud_free_tlb(tlb, pud, addr)  pud_free((tlb)->mm, pud)
>  #endif /* __PAGETABLE_PMD_FOLDED */
>
>  #define pmd_pgtable(pmd)       pmd_page(pmd)
> diff --git a/arch/riscv/include/asm/pgtable-64.h b/arch/riscv/include/asm/pgtable-64.h
> index b15f70a1fdfa..c84c31fbf8da 100644
> --- a/arch/riscv/include/asm/pgtable-64.h
> +++ b/arch/riscv/include/asm/pgtable-64.h
> @@ -8,16 +8,32 @@
>
>  #include <linux/const.h>
>
> -#define PGDIR_SHIFT     30
> +extern bool pgtable_l4_enabled;
> +
> +#define PGDIR_SHIFT     (pgtable_l4_enabled ? 39 : 30)
>  /* Size of region mapped by a page global directory */
>  #define PGDIR_SIZE      (_AC(1, UL) << PGDIR_SHIFT)
>  #define PGDIR_MASK      (~(PGDIR_SIZE - 1))
>
> +/* pud is folded into pgd in case of 3-level page table */
> +#define PUD_SHIFT      30
> +#define PUD_SIZE       (_AC(1, UL) << PUD_SHIFT)
> +#define PUD_MASK       (~(PUD_SIZE - 1))
> +
>  #define PMD_SHIFT       21
>  /* Size of region mapped by a page middle directory */
>  #define PMD_SIZE        (_AC(1, UL) << PMD_SHIFT)
>  #define PMD_MASK        (~(PMD_SIZE - 1))
>
> +/* Page Upper Directory entry */
> +typedef struct {
> +       unsigned long pud;
> +} pud_t;
> +
> +#define pud_val(x)      ((x).pud)
> +#define __pud(x)        ((pud_t) { (x) })
> +#define PTRS_PER_PUD    (PAGE_SIZE / sizeof(pud_t))
> +
>  /* Page Middle Directory entry */
>  typedef struct {
>         unsigned long pmd;
> @@ -60,6 +76,16 @@ static inline void pud_clear(pud_t *pudp)
>         set_pud(pudp, __pud(0));
>  }
>
> +static inline pud_t pfn_pud(unsigned long pfn, pgprot_t prot)
> +{
> +       return __pud((pfn << _PAGE_PFN_SHIFT) | pgprot_val(prot));
> +}
> +
> +static inline unsigned long _pud_pfn(pud_t pud)
> +{
> +       return pud_val(pud) >> _PAGE_PFN_SHIFT;
> +}
> +
>  static inline unsigned long pud_page_vaddr(pud_t pud)
>  {
>         return (unsigned long)pfn_to_virt(pud_val(pud) >> _PAGE_PFN_SHIFT);
> @@ -70,6 +96,15 @@ static inline struct page *pud_page(pud_t pud)
>         return pfn_to_page(pud_val(pud) >> _PAGE_PFN_SHIFT);
>  }
>
> +#define mm_pud_folded  mm_pud_folded
> +static inline bool mm_pud_folded(struct mm_struct *mm)
> +{
> +       if (pgtable_l4_enabled)
> +               return false;
> +
> +       return true;
> +}
> +
>  #define pmd_index(addr) (((addr) >> PMD_SHIFT) & (PTRS_PER_PMD - 1))
>
>  static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
> @@ -90,4 +125,64 @@ static inline unsigned long _pmd_pfn(pmd_t pmd)
>  #define pmd_ERROR(e) \
>         pr_err("%s:%d: bad pmd %016lx.\n", __FILE__, __LINE__, pmd_val(e))
>
> +#define pud_ERROR(e)   \
> +       pr_err("%s:%d: bad pud %016lx.\n", __FILE__, __LINE__, pud_val(e))
> +
> +static inline void set_p4d(p4d_t *p4dp, p4d_t p4d)
> +{
> +       if (pgtable_l4_enabled)
> +               *p4dp = p4d;
> +       else
> +               set_pud((pud_t *)p4dp, (pud_t){ p4d_val(p4d) });
> +}
> +
> +static inline int p4d_none(p4d_t p4d)
> +{
> +       if (pgtable_l4_enabled)
> +               return (p4d_val(p4d) == 0);
> +
> +       return 0;
> +}
> +
> +static inline int p4d_present(p4d_t p4d)
> +{
> +       if (pgtable_l4_enabled)
> +               return (p4d_val(p4d) & _PAGE_PRESENT);
> +
> +       return 1;
> +}
> +
> +static inline int p4d_bad(p4d_t p4d)
> +{
> +       if (pgtable_l4_enabled)
> +               return !p4d_present(p4d);
> +
> +       return 0;
> +}
> +
> +static inline void p4d_clear(p4d_t *p4d)
> +{
> +       if (pgtable_l4_enabled)
> +               set_p4d(p4d, __p4d(0));
> +}
> +
> +static inline unsigned long p4d_page_vaddr(p4d_t p4d)
> +{
> +       if (pgtable_l4_enabled)
> +               return (unsigned long)pfn_to_virt(
> +                               p4d_val(p4d) >> _PAGE_PFN_SHIFT);
> +
> +       return pud_page_vaddr((pud_t) { p4d_val(p4d) });
> +}
> +
> +#define pud_index(addr) (((addr) >> PUD_SHIFT) & (PTRS_PER_PUD - 1))
> +
> +static inline pud_t *pud_offset(p4d_t *p4d, unsigned long address)
> +{
> +       if (pgtable_l4_enabled)
> +               return (pud_t *)p4d_page_vaddr(*p4d) + pud_index(address);
> +
> +       return (pud_t *)p4d;
> +}
> +
>  #endif /* _ASM_RISCV_PGTABLE_64_H */
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 8e96315b3366..b8a8ba69d0a2 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -20,12 +20,14 @@
>   * the kernel.
>   */
>  #define KERNEL_VIRT_ADDR       (VMALLOC_END - SZ_2G + 1)
> -#define KERNEL_LINK_ADDR       KERNEL_VIRT_ADDR
> +#define KERNEL_LINK_ADDR       (VMALLOC_LINK_END - SZ_2G + 1)
>
>  #define VMALLOC_SIZE     (KERN_VIRT_SIZE >> 1)
>  #define VMALLOC_END      (PAGE_OFFSET - 1)
>  #define VMALLOC_START    (PAGE_OFFSET - VMALLOC_SIZE)
>
> +#define VMALLOC_LINK_END       (_AC(CONFIG_PAGE_OFFSET, UL) - 1)
> +
>  #define BPF_JIT_REGION_SIZE    (SZ_128M)
>  #define BPF_JIT_REGION_START   (kernel_virt_addr)
>  #define BPF_JIT_REGION_END     (kernel_virt_addr + BPF_JIT_REGION_SIZE)
> @@ -67,8 +69,7 @@
>
>  #ifndef __ASSEMBLY__
>
> -/* Page Upper Directory not used in RISC-V */
> -#include <asm-generic/pgtable-nopud.h>
> +#include <asm-generic/pgtable-nop4d.h>
>  #include <asm/page.h>
>  #include <asm/tlbflush.h>
>  #include <linux/mm_types.h>
> @@ -81,7 +82,7 @@
>
>  #ifdef CONFIG_MMU
>  #ifdef CONFIG_64BIT
> -#define VA_BITS                39
> +#define VA_BITS                (pgtable_l4_enabled ? 48 : 39)
>  #define PA_BITS                56
>  #else
>  #define VA_BITS                32
> diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> index 8f5bb7731327..0632c4834c68 100644
> --- a/arch/riscv/kernel/head.S
> +++ b/arch/riscv/kernel/head.S
> @@ -62,7 +62,8 @@ relocate:
>
>         /* Compute satp for kernel page tables, but don't load it yet */
>         srl a2, a0, PAGE_SHIFT
> -       li a1, SATP_MODE
> +       la a1, satp_mode
> +       REG_L a1, 0(a1)
>         or a2, a2, a1
>
>         /*
> diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
> index 613ec81a8979..6830504f8b11 100644
> --- a/arch/riscv/mm/context.c
> +++ b/arch/riscv/mm/context.c
> @@ -9,6 +9,8 @@
>  #include <asm/cacheflush.h>
>  #include <asm/mmu_context.h>
>
> +extern u64 satp_mode;
> +
>  /*
>   * When necessary, performs a deferred icache flush for the given MM context,
>   * on the local CPU.  RISC-V has no direct mechanism for instruction cache
> @@ -59,7 +61,7 @@ void switch_mm(struct mm_struct *prev, struct mm_struct *next,
>         cpumask_set_cpu(cpu, mm_cpumask(next));
>
>  #ifdef CONFIG_MMU
> -       csr_write(CSR_SATP, virt_to_pfn(next->pgd) | SATP_MODE);
> +       csr_write(CSR_SATP, virt_to_pfn(next->pgd) | satp_mode);
>         local_flush_tlb_all();
>  #endif
>
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 5782cae58ac2..bad8da099ff6 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -25,8 +25,23 @@
>
>  #include "../kernel/head.h"
>
> -unsigned long kernel_virt_addr = KERNEL_VIRT_ADDR;
> +#ifdef CONFIG_64BIT
> +u64 satp_mode = IS_ENABLED(CONFIG_MAXPHYSMEM_2GB) ?
> +                               SATP_MODE_39 : SATP_MODE_48;
> +bool pgtable_l4_enabled = IS_ENABLED(CONFIG_MAXPHYSMEM_2GB) ? false : true;
> +#else
> +u64 satp_mode = SATP_MODE_32;
> +bool pgtable_l4_enabled;
> +#endif
> +EXPORT_SYMBOL(pgtable_l4_enabled);
> +EXPORT_SYMBOL(satp_mode);
> +
> +unsigned long kernel_virt_addr;
>  EXPORT_SYMBOL(kernel_virt_addr);
> +#ifdef CONFIG_RELOCATABLE
> +unsigned long __page_offset = _AC(CONFIG_PAGE_OFFSET, UL);
> +EXPORT_SYMBOL(__page_offset);
> +#endif
>
>  unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
>                                                         __page_aligned_bss;
> @@ -254,9 +269,12 @@ static void __init create_pte_mapping(pte_t *ptep,
>
>  #ifndef __PAGETABLE_PMD_FOLDED
>
> +pud_t trampoline_pud[PTRS_PER_PUD] __page_aligned_bss;
>  pmd_t trampoline_pmd[PTRS_PER_PMD] __page_aligned_bss;
> +pud_t fixmap_pud[PTRS_PER_PUD] __page_aligned_bss;
>  pmd_t fixmap_pmd[PTRS_PER_PMD] __page_aligned_bss;
>  pmd_t early_pmd[PTRS_PER_PMD] __initdata __aligned(PAGE_SIZE);
> +pud_t early_pud[PTRS_PER_PUD] __initdata __aligned(PAGE_SIZE);
>
>  static pmd_t *__init get_pmd_virt(phys_addr_t pa)
>  {
> @@ -273,7 +291,8 @@ static phys_addr_t __init alloc_pmd(uintptr_t va)
>         if (mmu_enabled)
>                 return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>
> -       BUG_ON((va - kernel_virt_addr) >> PGDIR_SHIFT);
> +       /* Only one PMD is available for early mapping */
> +       BUG_ON((va - kernel_virt_addr) >> PUD_SHIFT);
>
>         return (uintptr_t)early_pmd;
>  }
> @@ -305,19 +324,70 @@ static void __init create_pmd_mapping(pmd_t *pmdp,
>         create_pte_mapping(ptep, va, pa, sz, prot);
>  }
>
> -#define pgd_next_t             pmd_t
> -#define alloc_pgd_next(__va)   alloc_pmd(__va)
> -#define get_pgd_next_virt(__pa)        get_pmd_virt(__pa)
> +static pud_t *__init get_pud_virt(phys_addr_t pa)
> +{
> +       if (mmu_enabled) {
> +               clear_fixmap(FIX_PUD);
> +               return (pud_t *)set_fixmap_offset(FIX_PUD, pa);
> +       } else {
> +               return (pud_t *)((uintptr_t)pa);
> +       }
> +}
> +
> +static phys_addr_t __init alloc_pud(uintptr_t va)
> +{
> +       if (mmu_enabled)
> +               return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
> +
> +       /* Only one PUD is available for early mapping */
> +       BUG_ON((va - kernel_virt_addr) >> PGDIR_SHIFT);
> +
> +       return (uintptr_t)early_pud;
> +}
> +
> +static void __init create_pud_mapping(pud_t *pudp,
> +                                     uintptr_t va, phys_addr_t pa,
> +                                     phys_addr_t sz, pgprot_t prot)
> +{
> +       pmd_t *nextp;
> +       phys_addr_t next_phys;
> +       uintptr_t pud_index = pud_index(va);
> +
> +       if (sz == PUD_SIZE) {
> +               if (pud_val(pudp[pud_index]) == 0)
> +                       pudp[pud_index] = pfn_pud(PFN_DOWN(pa), prot);
> +               return;
> +       }
> +
> +       if (pud_val(pudp[pud_index]) == 0) {
> +               next_phys = alloc_pmd(va);
> +               pudp[pud_index] = pfn_pud(PFN_DOWN(next_phys), PAGE_TABLE);
> +               nextp = get_pmd_virt(next_phys);
> +               memset(nextp, 0, PAGE_SIZE);
> +       } else {
> +               next_phys = PFN_PHYS(_pud_pfn(pudp[pud_index]));
> +               nextp = get_pmd_virt(next_phys);
> +       }
> +
> +       create_pmd_mapping(nextp, va, pa, sz, prot);
> +}
> +
> +#define pgd_next_t             pud_t
> +#define alloc_pgd_next(__va)   alloc_pud(__va)
> +#define get_pgd_next_virt(__pa)        get_pud_virt(__pa)
>  #define create_pgd_next_mapping(__nextp, __va, __pa, __sz, __prot)     \
> -       create_pmd_mapping(__nextp, __va, __pa, __sz, __prot)
> -#define fixmap_pgd_next                fixmap_pmd
> +       create_pud_mapping(__nextp, __va, __pa, __sz, __prot)
> +#define fixmap_pgd_next                (pgtable_l4_enabled ?                   \
> +                       (uintptr_t)fixmap_pud : (uintptr_t)fixmap_pmd)
> +#define trampoline_pgd_next    (pgtable_l4_enabled ?                   \
> +                       (uintptr_t)trampoline_pud : (uintptr_t)trampoline_pmd)
>  #else
>  #define pgd_next_t             pte_t
>  #define alloc_pgd_next(__va)   alloc_pte(__va)
>  #define get_pgd_next_virt(__pa)        get_pte_virt(__pa)
>  #define create_pgd_next_mapping(__nextp, __va, __pa, __sz, __prot)     \
>         create_pte_mapping(__nextp, __va, __pa, __sz, __prot)
> -#define fixmap_pgd_next                fixmap_pte
> +#define fixmap_pgd_next                ((uintptr_t)fixmap_pte)
>  #endif
>
>  static void __init create_pgd_mapping(pgd_t *pgdp,
> @@ -328,6 +398,13 @@ static void __init create_pgd_mapping(pgd_t *pgdp,
>         phys_addr_t next_phys;
>         uintptr_t pgd_index = pgd_index(va);
>
> +#ifndef __PAGETABLE_PMD_FOLDED
> +       if (!pgtable_l4_enabled) {
> +               create_pud_mapping((pud_t *)pgdp, va, pa, sz, prot);
> +               return;
> +       }
> +#endif
> +
>         if (sz == PGDIR_SIZE) {
>                 if (pgd_val(pgdp[pgd_index]) == 0)
>                         pgdp[pgd_index] = pfn_pgd(PFN_DOWN(pa), prot);
> @@ -419,6 +496,47 @@ void __init relocate_kernel(uintptr_t load_pa)
>         }
>  }
>
> +#if defined(CONFIG_64BIT) && !defined(CONFIG_MAXPHYSMEM_2GB)
> +void disable_pgtable_l4(void)
> +{
> +       pgtable_l4_enabled = false;
> +       __page_offset = PAGE_OFFSET_L3;
> +       satp_mode = SATP_MODE_39;
> +}
> +
> +/* There is a simple way to determine if 4-level is supported by the
> + * underlying hardware: establish 1:1 mapping in 4-level page table mode
> + * then read SATP to see if the configuration was taken into account
> + * meaning sv48 is supported.
> + */
> +asmlinkage __init void set_satp_mode(uintptr_t load_pa)
> +{
> +       u64 identity_satp, hw_satp;
> +       int cpus_node;
> +
> +       create_pgd_mapping(early_pg_dir, load_pa, (uintptr_t)early_pud,
> +                          PGDIR_SIZE, PAGE_TABLE);
> +       create_pud_mapping(early_pud, load_pa, (uintptr_t)early_pmd,
> +                          PUD_SIZE, PAGE_TABLE);
> +       create_pmd_mapping(early_pmd, load_pa, load_pa,
> +                          PMD_SIZE, PAGE_KERNEL_EXEC);
> +
> +       identity_satp = PFN_DOWN((uintptr_t)&early_pg_dir) | satp_mode;
> +       local_flush_tlb_all();
> +       csr_write(CSR_SATP, identity_satp);
> +
> +       hw_satp = csr_read(CSR_SATP);
> +       csr_write(CSR_SATP, 0ULL);
> +       local_flush_tlb_all();
> +
> +       if (hw_satp != identity_satp)
> +               disable_pgtable_l4();
> +
> +       memset(early_pg_dir, 0, PAGE_SIZE);
> +       memset(early_pud, 0, PAGE_SIZE);
> +       memset(early_pmd, 0, PAGE_SIZE);
> +}
> +#endif
>  #endif
>
>  static uintptr_t load_pa, load_sz;
> @@ -442,9 +560,14 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>         load_pa = (uintptr_t)(&_start);
>         load_sz = (uintptr_t)(&_end) - load_pa;
>
> +#if defined(CONFIG_64BIT) && !defined(CONFIG_MAXPHYSMEM_2GB)
> +       set_satp_mode(load_pa);
> +#endif
> +
> +       kernel_virt_addr = KERNEL_VIRT_ADDR;
> +
>         va_pa_offset = PAGE_OFFSET - load_pa;
>         va_kernel_pa_offset = kernel_virt_addr - load_pa;
> -
>         pfn_base = PFN_DOWN(load_pa);
>
>  #ifdef CONFIG_RELOCATABLE
> @@ -473,15 +596,22 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>
>         /* Setup early PGD for fixmap */
>         create_pgd_mapping(early_pg_dir, FIXADDR_START,
> -                          (uintptr_t)fixmap_pgd_next, PGDIR_SIZE, PAGE_TABLE);
> +                          fixmap_pgd_next, PGDIR_SIZE, PAGE_TABLE);
>
>  #ifndef __PAGETABLE_PMD_FOLDED
> -       /* Setup fixmap PMD */
> +       /* Setup fixmap PUD and PMD */
> +       if (pgtable_l4_enabled)
> +               create_pud_mapping(fixmap_pud, FIXADDR_START,
> +                          (uintptr_t)fixmap_pmd, PUD_SIZE, PAGE_TABLE);
>         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, kernel_virt_addr,
> -                          (uintptr_t)trampoline_pmd, PGDIR_SIZE, PAGE_TABLE);
> +                          trampoline_pgd_next, PGDIR_SIZE, PAGE_TABLE);
> +       if (pgtable_l4_enabled)
> +               create_pud_mapping(trampoline_pud, kernel_virt_addr,
> +                          (uintptr_t)trampoline_pmd, PUD_SIZE, PAGE_TABLE);
>         create_pmd_mapping(trampoline_pmd, kernel_virt_addr,
>                            load_pa, PMD_SIZE, PAGE_KERNEL_EXEC);
>  #else
> @@ -558,12 +688,13 @@ static void __init setup_vm_final(void)
>
>         vm_area_add_early(&vm_kernel);
>
> -       /* Clear fixmap PTE and PMD mappings */
> +       /* Clear fixmap page table mappings */
>         clear_fixmap(FIX_PTE);
>         clear_fixmap(FIX_PMD);
> +       clear_fixmap(FIX_PUD);
>
>         /* Move to swapper page table */
> -       csr_write(CSR_SATP, PFN_DOWN(__pa_symbol(swapper_pg_dir)) | SATP_MODE);
> +       csr_write(CSR_SATP, PFN_DOWN(__pa_symbol(swapper_pg_dir)) | satp_mode);
>         local_flush_tlb_all();
>  }
>
> --
> 2.20.1
>

Looks good to me.

Reviewed-by: Anup Patel <anup@brainfault.org>

Regards,
Anup