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Date:   Fri, 03 Apr 2020 08:53:13 -0700 (PDT)
Subject:     Re: [RFC PATCH 4/7] riscv: Implement sv48 support
In-Reply-To: <20200322110028.18279-5-alex@ghiti.fr>
CC:     Paul Walmsley <paul.walmsley@sifive.com>, zong.li@sifive.com,
        anup@brainfault.org, Christoph Hellwig <hch@lst.de>,
        linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
        alex@ghiti.fr
From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     alex@ghiti.fr
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On Sun, 22 Mar 2020 04:00:25 PDT (-0700), 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.

Ya, I think that's the right way to go about this.  There's no reason to
rely on duplicate DT mechanisms for things the ISA defines for us.

>
> 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

I assume this means you're relying on relocation to move the kernel around
independently of PAGE_OFFSET in order to fold in the missing page table level?
That seems reasonable, but it does impose a performance penalty as relocatable
kernels necessitate slower generated code.  Additionally, there will likely be
a performance penalty due to the extra memory access on TLB misses that is
unnecessary for workloads that don't necessitate the longer VA width on
machines that support it.

I think the best bet here would be to have a Kconfig option for the number of
page table levels (which could be MAXPHYSMEM or a second partially free
parameter) and then another boolean argument along the lines of "also support
machines with smaller VA widths".  It seems best to turn on the largest VA
width and support for folding by default, as I assume that's what distros would
do.

I didn't really look closely at the rest of this, but it generally smells OK.
The diff will need to be somewhat different for the next version, anyway :)

Thanks for doing this!

> 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