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Subject: Re: [RFC PATCH 4/7] riscv: Implement sv48 support
To:     Anup Patel <anup@brainfault.org>
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>
References: <20200322110028.18279-1-alex@ghiti.fr>
 <20200322110028.18279-5-alex@ghiti.fr>
 <CAAhSdy3BR-jU8tshU58VA3bZ_Ui_Rbyvo86eHNeAZ1CeWGU=bQ@mail.gmail.com>
From:   Alex Ghiti <alex@ghiti.fr>
Message-ID: <81e12c45-9041-c95a-9a46-27c985a734d4@ghiti.fr>
Date:   Tue, 31 Mar 2020 12:31:45 -0400
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Hi Anup,

On 3/26/20 3:00 AM, Anup Patel wrote:
> On Sun, Mar 22, 2020 at 4:34 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.
>>
>> By default, the kernel will try to boot with a 4-level page table. If the
>> underlying hardware does not support it, we will automatically fallback to
>> a standard 3-level page table by folding the new PUD level into PGDIR
>> level.
>>
>> Early page table preparation is too early in the boot process to use any
>> device-tree entry, then in order to detect HW capabilities at runtime, we
>> use SATP feature that ignores writes with an unsupported mode. The current
>> mode used by the kernel is then made available through cpuinfo.
> 
> Overall the patch look fine but I don't agree with the strategy of detecting
> SV48 mode in relocate() of head.S.
> 
> Instead of this, I suggest that we have a separate PATCH before this
> PATCH which just adds satp_mode global variable.
> 
> This PATCH can detect-n-update both satp_mode and pgtable_l4_enabled
> variables in setup_vm() (i.e. C sources) before setting up initial page
> tables. This way we can avoid adding setup_vm_fold_pud() function and
> in-future we will not require any changes in head.S when a new page table
> format shows-up to support 64K pages. The means MMU mode detection
> will always be restricted to setup_vm() in mm/init.c.
> 
> To achieve Sv48 mode detection in C sources, we just need one 4KB
> page for PGD (e.g. trampoline_pg_dir). To detect Sv48, we create flat
> identity mapping directly in PGD assuming Sv48 is available and try
> enabling Sv48. If Sv48 is enabled successfully then reading back SATP
> CSR will show mode as Sv48 otherwise mode will not be set.
> 
> As an example, refer __detect_pgtbl_mode() function of Xvisor at
> https://github.com/avpatel/xvisor-next/blob/master/arch/riscv/cpu/generic/cpu_mmu_initial_pgtbl.c
> 

Nice ! Indeed that sounds easier this way since I would not have to call 
relocate again and then setup_vm_fold_pud. Quite a good idea :)

Thanks for your review of the other patches Anup,

Alex

> Regards,
> Anup
> 
>>
>> 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 |  98 ++++++++++++++++++++-
>>   arch/riscv/include/asm/pgtable.h    |   5 +-
>>   arch/riscv/kernel/head.S            |  37 ++++++--
>>   arch/riscv/mm/context.c             |   4 +-
>>   arch/riscv/mm/init.c                | 128 +++++++++++++++++++++++++---
>>   10 files changed, 302 insertions(+), 31 deletions(-)
>>
>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>> index a475c78e66bc..79560e94cc7c 100644
>> --- a/arch/riscv/Kconfig
>> +++ b/arch/riscv/Kconfig
>> @@ -66,6 +66,7 @@ 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
>> @@ -104,7 +105,7 @@ 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
>> @@ -148,8 +149,11 @@ 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 435b65532e29..3828d55af85e 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 42d2c42f3cc9..26e7799c5675 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_EARLYCON_MEM_BASE,
>>          __end_of_fixed_addresses
>>   };
>> diff --git a/arch/riscv/include/asm/page.h b/arch/riscv/include/asm/page.h
>> index 691f2f9ded2f..f1a26a0690ef 100644
>> --- a/arch/riscv/include/asm/page.h
>> +++ b/arch/riscv/include/asm/page.h
>> @@ -32,11 +32,19 @@
>>    * physical memory (aligned on a page boundary).
>>    */
>>   #ifdef CONFIG_RELOCATABLE
>> -extern unsigned long kernel_virt_addr;
>>   #define PAGE_OFFSET            kernel_virt_addr
>> +
>> +#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
>> +#define PAGE_OFFSET_L4         _AC(CONFIG_PAGE_OFFSET, UL)
>> +#endif /* CONFIG_64BIT */
>>   #else
>>   #define PAGE_OFFSET            _AC(CONFIG_PAGE_OFFSET, UL)
>> -#endif
>> +#endif /* CONFIG_RELOCATABLE */
>>
>>   #define KERN_VIRT_SIZE         -PAGE_OFFSET
>>
>> @@ -104,6 +112,9 @@ extern unsigned long pfn_base;
>>
>>   extern unsigned long max_low_pfn;
>>   extern unsigned long min_low_pfn;
>> +#ifdef CONFIG_RELOCATABLE
>> +extern unsigned long kernel_virt_addr;
>> +#endif
>>
>>   #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)
>> 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..cc4ffbe778f3 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;
>> @@ -25,7 +41,6 @@ typedef struct {
>>
>>   #define pmd_val(x)      ((x).pmd)
>>   #define __pmd(x)        ((pmd_t) { (x) })
>> -
>>   #define PTRS_PER_PMD    (PAGE_SIZE / sizeof(pmd_t))
>>
>>   static inline int pud_present(pud_t pud)
>> @@ -60,6 +75,16 @@ 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 +95,15 @@ 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 +124,64 @@ 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 dce401eed1d3..06361db3f486 100644
>> --- a/arch/riscv/include/asm/pgtable.h
>> +++ b/arch/riscv/include/asm/pgtable.h
>> @@ -13,8 +13,7 @@
>>
>>   #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>
>> @@ -27,7 +26,7 @@
>>
>>   #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 1c2fbefb8786..22617bd7477f 100644
>> --- a/arch/riscv/kernel/head.S
>> +++ b/arch/riscv/kernel/head.S
>> @@ -113,6 +113,8 @@ clear_bss_done:
>>          call setup_vm
>>   #ifdef CONFIG_MMU
>>          la a0, early_pg_dir
>> +       la a1, satp_mode
>> +       REG_L a1, (a1)
>>          call relocate
>>   #endif /* CONFIG_MMU */
>>
>> @@ -131,24 +133,28 @@ clear_bss_done:
>>   #ifdef CONFIG_MMU
>>   relocate:
>>   #ifdef CONFIG_RELOCATABLE
>> -       /* Relocate return address */
>> -       la a1, kernel_virt_addr
>> -       REG_L a1, 0(a1)
>> +       /*
>> +        * Relocate return address but save it in case 4-level page table is
>> +        * not supported.
>> +        */
>> +       mv s1, ra
>> +       la a3, kernel_virt_addr
>> +       REG_L a3, 0(a3)
>>   #else
>> -       li a1, PAGE_OFFSET
>> +       li a3, PAGE_OFFSET
>>   #endif
>>          la a2, _start
>> -       sub a1, a1, a2
>> -       add ra, ra, a1
>> +       sub a3, a3, a2
>> +       add ra, ra, a3
>>
>>          /* Point stvec to virtual address of intruction after satp write */
>>          la a2, 1f
>> -       add a2, a2, a1
>> +       add a2, a2, a3
>>          csrw CSR_TVEC, a2
>>
>> +       /* First try with a 4-level page table */
>>          /* Compute satp for kernel page tables, but don't load it yet */
>>          srl a2, a0, PAGE_SHIFT
>> -       li a1, SATP_MODE
>>          or a2, a2, a1
>>
>>          /*
>> @@ -162,6 +168,19 @@ relocate:
>>          or a0, a0, a1
>>          sfence.vma
>>          csrw CSR_SATP, a0
>> +#if defined(CONFIG_RELOCATABLE) && defined(CONFIG_64BIT)
>> +       /*
>> +        * If we fall through here, that means the HW does not support SV48.
>> +        * We need a 3-level page table then simply fold pud into pgd level
>> +        * and finally jump back to relocate with 3-level parameters.
>> +        */
>> +       call setup_vm_fold_pud
>> +
>> +       la a0, early_pg_dir
>> +       li a1, SATP_MODE_39
>> +       mv ra, s1
>> +       tail relocate
>> +#endif
>>   .align 2
>>   1:
>>          /* Set trap vector to spin forever to help debug */
>> @@ -213,6 +232,8 @@ relocate:
>>   #ifdef CONFIG_MMU
>>          /* Enable virtual memory and relocate to virtual address */
>>          la a0, swapper_pg_dir
>> +       la a1, satp_mode
>> +       REG_L a1, (a1)
>>          call relocate
>>   #endif
>>
>> diff --git a/arch/riscv/mm/context.c b/arch/riscv/mm/context.c
>> index 613ec81a8979..152b423c02ea 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 uint64_t 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 18bbb426848e..ad96667d2ab6 100644
>> --- a/arch/riscv/mm/init.c
>> +++ b/arch/riscv/mm/init.c
>> @@ -24,6 +24,17 @@
>>
>>   #include "../kernel/head.h"
>>
>> +#ifdef CONFIG_64BIT
>> +uint64_t 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
>> +uint64_t satp_mode = SATP_MODE_32;
>> +bool pgtable_l4_enabled = false;
>> +#endif
>> +EXPORT_SYMBOL(pgtable_l4_enabled);
>> +EXPORT_SYMBOL(satp_mode);
>> +
>>   unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)]
>>                                                          __page_aligned_bss;
>>   EXPORT_SYMBOL(empty_zero_page);
>> @@ -245,9 +256,12 @@ 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)
>>   {
>> @@ -264,7 +278,8 @@ static phys_addr_t __init alloc_pmd(uintptr_t va)
>>          if (mmu_enabled)
>>                  return memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE);
>>
>> -       BUG_ON((va - PAGE_OFFSET) >> PGDIR_SHIFT);
>> +       /* Only one PMD is available for early mapping */
>> +       BUG_ON((va - PAGE_OFFSET) >> PUD_SHIFT);
>>
>>          return (uintptr_t)early_pmd;
>>   }
>> @@ -296,19 +311,70 @@ 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 - PAGE_OFFSET) >> 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,
>> @@ -319,6 +385,13 @@ 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);
>> @@ -449,15 +522,22 @@ 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, PAGE_OFFSET,
>> -                          (uintptr_t)trampoline_pmd, PGDIR_SIZE, PAGE_TABLE);
>> +                          trampoline_pgd_next, PGDIR_SIZE, PAGE_TABLE);
>> +       if (pgtable_l4_enabled)
>> +               create_pud_mapping(trampoline_pud, PAGE_OFFSET,
>> +                          (uintptr_t)trampoline_pmd, PUD_SIZE, PAGE_TABLE);
>>          create_pmd_mapping(trampoline_pmd, PAGE_OFFSET,
>>                             load_pa, PMD_SIZE, PAGE_KERNEL_EXEC);
>>   #else
>> @@ -490,6 +570,29 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>>          dtb_early_pa = dtb_pa;
>>   }
>>
>> +#if defined(CONFIG_RELOCATABLE) && defined(CONFIG_64BIT)
>> +/*
>> + * This function is called only if the current kernel is 64bit and the HW
>> + * does not support sv48.
>> + */
>> +asmlinkage __init void setup_vm_fold_pud(void)
>> +{
>> +       pgtable_l4_enabled = false;
>> +       kernel_virt_addr = PAGE_OFFSET_L3;
>> +       satp_mode = SATP_MODE_39;
>> +
>> +       /*
>> +        * PTE/PMD levels do not need to be cleared as they are common between
>> +        * 3- and 4-level page tables: the 30 least significant bits
>> +        * (2 * 9 + 12) are common.
>> +        */
>> +       memset(trampoline_pg_dir, 0, sizeof(pgd_t) * PTRS_PER_PGD);
>> +       memset(early_pg_dir, 0, sizeof(pgd_t) * PTRS_PER_PGD);
>> +
>> +       setup_vm(dtb_early_pa);
>> +}
>> +#endif
>> +
>>   static void __init setup_vm_final(void)
>>   {
>>          uintptr_t va, map_size;
>> @@ -525,12 +628,13 @@ static void __init setup_vm_final(void)
>>                  }
>>          }
>>
>> -       /* 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();
>>   }
>>   #else
>> --
>> 2.20.1
>>