RE: [RFC PATCH v1 57/57] arm64: Enable boot-time page size selection

[Michael Kelley <mhklinux@outlook.com>]

From: Ryan Roberts <ryan.roberts@arm.com> Sent: Monday, October 14, 2024 3:59 AM
> 
> Introduce a new Kconfig, ARM64_BOOT_TIME_PAGE_SIZE, which can be
> selected instead of a page size. When selected, the resulting kernel's
> page size can be configured at boot via the command line.
> 
> For now, boot-time page size kernels are limited to 48-bit VA, since
> more work is required to support LPA2. Additionally MMAP_RND_BITS and
> SECTION_SIZE_BITS are configured for the worst case (64K pages). Future
> work could be implemented to be able to configure these at boot time for
> optimial page size-specific values.
> 
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
> 
> ***NOTE***
> Any confused maintainers may want to read the cover note here for context:
> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@arm.com/
> 
>  arch/arm64/Kconfig                         | 26 ++++++++++---
>  arch/arm64/include/asm/kvm_hyp.h           | 11 ++++++
>  arch/arm64/include/asm/pgtable-geometry.h  | 22 ++++++++++-
>  arch/arm64/include/asm/pgtable-hwdef.h     |  6 +--
>  arch/arm64/include/asm/pgtable.h           | 10 ++++-
>  arch/arm64/include/asm/sparsemem.h         |  4 ++
>  arch/arm64/kernel/image-vars.h             | 11 ++++++
>  arch/arm64/kernel/image.h                  |  4 ++
>  arch/arm64/kernel/pi/map_kernel.c          | 45 ++++++++++++++++++++++
>  arch/arm64/kvm/arm.c                       | 10 +++++
>  arch/arm64/kvm/hyp/nvhe/Makefile           |  1 +
>  arch/arm64/kvm/hyp/nvhe/pgtable-geometry.c | 16 ++++++++
>  arch/arm64/mm/Makefile                     |  1 +
>  arch/arm64/mm/pgd.c                        | 10 +++--
>  arch/arm64/mm/pgtable-geometry.c           | 24 ++++++++++++
>  drivers/firmware/efi/libstub/arm64.c       |  3 +-
>  16 files changed, 187 insertions(+), 17 deletions(-)
>  create mode 100644 arch/arm64/kvm/hyp/nvhe/pgtable-geometry.c
>  create mode 100644 arch/arm64/mm/pgtable-geometry.c
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index a2f8ff354ca67..573d308741169 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -121,6 +121,7 @@ config ARM64
>  	select BUILDTIME_TABLE_SORT
>  	select CLONE_BACKWARDS
>  	select COMMON_CLK
> +	select CONSTRUCTORS if ARM64_BOOT_TIME_PAGE_SIZE
>  	select CPU_PM if (SUSPEND || CPU_IDLE)
>  	select CPUMASK_OFFSTACK if NR_CPUS > 256
>  	select CRC32
> @@ -284,18 +285,20 @@ config MMU
> 
>  config ARM64_CONT_PTE_SHIFT
>  	int
> +	depends on !ARM64_BOOT_TIME_PAGE_SIZE
>  	default 5 if PAGE_SIZE_64KB
>  	default 7 if PAGE_SIZE_16KB
>  	default 4
> 
>  config ARM64_CONT_PMD_SHIFT
>  	int
> +	depends on !ARM64_BOOT_TIME_PAGE_SIZE
>  	default 5 if PAGE_SIZE_64KB
>  	default 5 if PAGE_SIZE_16KB
>  	default 4
> 
>  config ARCH_MMAP_RND_BITS_MIN
> -	default 14 if PAGE_SIZE_64KB
> +	default 14 if ARM64_64K_PAGES || ARM64_BOOT_TIME_PAGE_SIZE
>  	default 16 if PAGE_SIZE_16KB
>  	default 18
> 
> @@ -306,15 +309,15 @@ config ARCH_MMAP_RND_BITS_MAX
>  	default 24 if ARM64_VA_BITS=39
>  	default 27 if ARM64_VA_BITS=42
>  	default 30 if ARM64_VA_BITS=47
> -	default 29 if ARM64_VA_BITS=48 && ARM64_64K_PAGES
> +	default 29 if ARM64_VA_BITS=48 && (ARM64_64K_PAGES ||
> ARM64_BOOT_TIME_PAGE_SIZE)
>  	default 31 if ARM64_VA_BITS=48 && ARM64_16K_PAGES
>  	default 33 if ARM64_VA_BITS=48
> -	default 14 if ARM64_64K_PAGES
> +	default 14 if ARM64_64K_PAGES || ARM64_BOOT_TIME_PAGE_SIZE
>  	default 16 if ARM64_16K_PAGES
>  	default 18
> 
>  config ARCH_MMAP_RND_COMPAT_BITS_MIN
> -	default 7 if ARM64_64K_PAGES
> +	default 7 if ARM64_64K_PAGES || ARM64_BOOT_TIME_PAGE_SIZE
>  	default 9 if ARM64_16K_PAGES
>  	default 11
> 
> @@ -362,6 +365,7 @@ config FIX_EARLYCON_MEM
> 
>  config PGTABLE_LEVELS
>  	int
> +	default 4 if ARM64_BOOT_TIME_PAGE_SIZE # Advertise max supported levels
>  	default 2 if ARM64_16K_PAGES && ARM64_VA_BITS_36
>  	default 2 if ARM64_64K_PAGES && ARM64_VA_BITS_42
>  	default 3 if ARM64_64K_PAGES && (ARM64_VA_BITS_48 ||
> ARM64_VA_BITS_52)
> @@ -1316,6 +1320,14 @@ config ARM64_64K_PAGES
>  	  look-up. AArch32 emulation requires applications compiled
>  	  with 64K aligned segments.
> 
> +config ARM64_BOOT_TIME_PAGE_SIZE
> +	bool "Boot-time selection"
> +	select HAVE_PAGE_SIZE_64KB # Advertise largest page size to core
> +	help
> +	  Select desired page size (4KB, 16KB or 64KB) at boot-time via the
> +	  kernel command line option "arm64.pagesize=4k", "arm64.pagesize=16k"
> +	  or "arm64.pagesize=64k".
> +
>  endchoice
> 
>  choice
> @@ -1348,6 +1360,7 @@ config ARM64_VA_BITS_48
>  config ARM64_VA_BITS_52
>  	bool "52-bit"
>  	depends on ARM64_PAN || !ARM64_SW_TTBR0_PAN
> +	depends on !ARM64_BOOT_TIME_PAGE_SIZE
>  	help
>  	  Enable 52-bit virtual addressing for userspace when explicitly
>  	  requested via a hint to mmap(). The kernel will also use 52-bit
> @@ -1588,9 +1601,10 @@ config XEN
>  # 4K  |       27          |      12      |       15             |         10              |
>  # 16K |       27          |      14      |       13             |         11              |
>  # 64K |       29          |      16      |       13             |         13              |
> +# BOOT|       29          |    16 (max)  |       13             |         13              |
>  config ARCH_FORCE_MAX_ORDER
>  	int
> -	default "13" if ARM64_64K_PAGES
> +	default "13" if ARM64_64K_PAGES || ARM64_BOOT_TIME_PAGE_SIZE
>  	default "11" if ARM64_16K_PAGES
>  	default "10"
>  	help
> @@ -1663,7 +1677,7 @@ config ARM64_TAGGED_ADDR_ABI
> 
>  menuconfig COMPAT
>  	bool "Kernel support for 32-bit EL0"
> -	depends on ARM64_4K_PAGES || EXPERT
> +	depends on ARM64_4K_PAGES || ARM64_BOOT_TIME_PAGE_SIZE || EXPERT
>  	select HAVE_UID16
>  	select OLD_SIGSUSPEND3
>  	select COMPAT_OLD_SIGACTION
> diff --git a/arch/arm64/include/asm/kvm_hyp.h
> b/arch/arm64/include/asm/kvm_hyp.h
> index c838309e4ec47..9397a14642afa 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -145,4 +145,15 @@ extern unsigned long kvm_nvhe_sym(__icache_flags);
>  extern unsigned int kvm_nvhe_sym(kvm_arm_vmid_bits);
>  extern unsigned int kvm_nvhe_sym(kvm_host_sve_max_vl);
> 
> +#ifdef CONFIG_ARM64_BOOT_TIME_PAGE_SIZE
> +extern int kvm_nvhe_sym(ptg_page_shift);
> +extern int kvm_nvhe_sym(ptg_pmd_shift);
> +extern int kvm_nvhe_sym(ptg_pud_shift);
> +extern int kvm_nvhe_sym(ptg_p4d_shift);
> +extern int kvm_nvhe_sym(ptg_pgdir_shift);
> +extern int kvm_nvhe_sym(ptg_cont_pte_shift);
> +extern int kvm_nvhe_sym(ptg_cont_pmd_shift);
> +extern int kvm_nvhe_sym(ptg_pgtable_levels);
> +#endif /* CONFIG_ARM64_BOOT_TIME_PAGE_SIZE */
> +
>  #endif /* __ARM64_KVM_HYP_H__ */
> diff --git a/arch/arm64/include/asm/pgtable-geometry.h
> b/arch/arm64/include/asm/pgtable-geometry.h
> index 62fe125909c08..18a8c8d499ecc 100644
> --- a/arch/arm64/include/asm/pgtable-geometry.h
> +++ b/arch/arm64/include/asm/pgtable-geometry.h
> @@ -6,16 +6,33 @@
>  #define ARM64_PAGE_SHIFT_16K	14
>  #define ARM64_PAGE_SHIFT_64K	16
> 
> +#ifdef CONFIG_ARM64_BOOT_TIME_PAGE_SIZE
> +#define PAGE_SHIFT_MIN		ARM64_PAGE_SHIFT_4K
> +#define PAGE_SHIFT_MAX		ARM64_PAGE_SHIFT_64K
> +#else /* CONFIG_ARM64_BOOT_TIME_PAGE_SIZE */
>  #define PAGE_SHIFT_MIN		CONFIG_PAGE_SHIFT
> +#define PAGE_SHIFT_MAX		CONFIG_PAGE_SHIFT
> +#endif /* CONFIG_ARM64_BOOT_TIME_PAGE_SIZE */
> +
>  #define PAGE_SIZE_MIN		(_AC(1, UL) << PAGE_SHIFT_MIN)
>  #define PAGE_MASK_MIN		(~(PAGE_SIZE_MIN-1))
> -
> -#define PAGE_SHIFT_MAX		CONFIG_PAGE_SHIFT
>  #define PAGE_SIZE_MAX		(_AC(1, UL) << PAGE_SHIFT_MAX)
>  #define PAGE_MASK_MAX		(~(PAGE_SIZE_MAX-1))
> 
>  #include <asm-generic/pgtable-geometry.h>
> 
> +#ifdef CONFIG_ARM64_BOOT_TIME_PAGE_SIZE
> +#ifndef __ASSEMBLY__
> +extern int ptg_page_shift;
> +extern int ptg_pmd_shift;
> +extern int ptg_pud_shift;
> +extern int ptg_p4d_shift;
> +extern int ptg_pgdir_shift;
> +extern int ptg_cont_pte_shift;
> +extern int ptg_cont_pmd_shift;
> +extern int ptg_pgtable_levels;
> +#endif /* __ASSEMBLY__ */
> +#else /* CONFIG_ARM64_BOOT_TIME_PAGE_SIZE */
>  #define ptg_page_shift		CONFIG_PAGE_SHIFT
>  #define ptg_pmd_shift		ARM64_HW_PGTABLE_LEVEL_SHIFT(2)
>  #define ptg_pud_shift		ARM64_HW_PGTABLE_LEVEL_SHIFT(1)
> @@ -24,5 +41,6 @@
>  #define ptg_cont_pte_shift	(CONFIG_ARM64_CONT_PTE_SHIFT + PAGE_SHIFT)
>  #define ptg_cont_pmd_shift	(CONFIG_ARM64_CONT_PMD_SHIFT + PMD_SHIFT)
>  #define ptg_pgtable_levels	CONFIG_PGTABLE_LEVELS
> +#endif /* CONFIG_ARM64_BOOT_TIME_PAGE_SIZE */
> 
>  #endif /* ASM_PGTABLE_GEOMETRY_H */
> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h
> b/arch/arm64/include/asm/pgtable-hwdef.h
> index ca8bcbc1fe220..da5404617acbf 100644
> --- a/arch/arm64/include/asm/pgtable-hwdef.h
> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
> @@ -52,7 +52,7 @@
>  #define PMD_SHIFT		ptg_pmd_shift
>  #define PMD_SIZE		(_AC(1, UL) << PMD_SHIFT)
>  #define PMD_MASK		(~(PMD_SIZE-1))
> -#define PTRS_PER_PMD		(1 << (PAGE_SHIFT - 3))
> +#define PTRS_PER_PMD		(ptg_pgtable_levels > 2 ? (1 << (PAGE_SHIFT -
> 3)) : 1)
>  #define MAX_PTRS_PER_PMD	(1 << (PAGE_SHIFT_MAX - 3))
>  #endif
> 
> @@ -63,7 +63,7 @@
>  #define PUD_SHIFT		ptg_pud_shift
>  #define PUD_SIZE		(_AC(1, UL) << PUD_SHIFT)
>  #define PUD_MASK		(~(PUD_SIZE-1))
> -#define PTRS_PER_PUD		(1 << (PAGE_SHIFT - 3))
> +#define PTRS_PER_PUD		(ptg_pgtable_levels > 3 ? (1 << (PAGE_SHIFT -
> 3)) : 1)
>  #define MAX_PTRS_PER_PUD	(1 << (PAGE_SHIFT_MAX - 3))
>  #endif
> 
> @@ -71,7 +71,7 @@
>  #define P4D_SHIFT		ptg_p4d_shift
>  #define P4D_SIZE		(_AC(1, UL) << P4D_SHIFT)
>  #define P4D_MASK		(~(P4D_SIZE-1))
> -#define PTRS_PER_P4D		(1 << (PAGE_SHIFT - 3))
> +#define PTRS_PER_P4D		(ptg_pgtable_levels > 4 ? (1 << (PAGE_SHIFT -
> 3)) : 1)
>  #define MAX_PTRS_PER_P4D	(1 << (PAGE_SHIFT_MAX - 3))
>  #endif
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 8ead41da715b0..ad9f75f5cc29a 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -755,7 +755,7 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd)
> 
>  static __always_inline bool pgtable_l3_enabled(void)
>  {
> -	return true;
> +	return ptg_pgtable_levels > 2;
>  }
> 
>  static inline bool mm_pmd_folded(const struct mm_struct *mm)
> @@ -888,6 +888,8 @@ static inline bool pgtable_l3_enabled(void) { return false; }
> 
>  static __always_inline bool pgtable_l4_enabled(void)
>  {
> +	if (IS_ENABLED(CONFIG_ARM64_BOOT_TIME_PAGE_SIZE))
> +		return ptg_pgtable_levels > 3;
>  	if (CONFIG_PGTABLE_LEVELS > 4 || !IS_ENABLED(CONFIG_ARM64_LPA2))
>  		return true;
>  	if (!alternative_has_cap_likely(ARM64_ALWAYS_BOOT))
> @@ -935,6 +937,8 @@ static inline phys_addr_t p4d_page_paddr(p4d_t p4d)
> 
>  static inline pud_t *p4d_to_folded_pud(p4d_t *p4dp, unsigned long addr)
>  {
> +	if (IS_ENABLED(CONFIG_ARM64_BOOT_TIME_PAGE_SIZE))
> +		return (pud_t *)p4dp;
>  	return (pud_t *)PTR_ALIGN_DOWN(p4dp, PAGE_SIZE) + pud_index(addr);
>  }
> 
> @@ -1014,6 +1018,8 @@ static inline bool pgtable_l4_enabled(void) { return false; }
> 
>  static __always_inline bool pgtable_l5_enabled(void)
>  {
> +	if (IS_ENABLED(CONFIG_ARM64_BOOT_TIME_PAGE_SIZE))
> +		return ptg_pgtable_levels > 4;
>  	if (!alternative_has_cap_likely(ARM64_ALWAYS_BOOT))
>  		return vabits_actual == VA_BITS;
>  	return alternative_has_cap_unlikely(ARM64_HAS_VA52);
> @@ -1059,6 +1065,8 @@ static inline phys_addr_t pgd_page_paddr(pgd_t pgd)
> 
>  static inline p4d_t *pgd_to_folded_p4d(pgd_t *pgdp, unsigned long addr)
>  {
> +	if (IS_ENABLED(CONFIG_ARM64_BOOT_TIME_PAGE_SIZE))
> +		return (p4d_t *)pgdp;
>  	return (p4d_t *)PTR_ALIGN_DOWN(pgdp, PAGE_SIZE) + p4d_index(addr);
>  }
> 
> diff --git a/arch/arm64/include/asm/sparsemem.h
> b/arch/arm64/include/asm/sparsemem.h
> index a05fdd54014f7..2daf1263ba638 100644
> --- a/arch/arm64/include/asm/sparsemem.h
> +++ b/arch/arm64/include/asm/sparsemem.h
> @@ -17,6 +17,10 @@
>   * entries could not be created for vmemmap mappings.
>   * 16K follows 4K for simplicity.
>   */
> +#ifdef CONFIG_ARM64_BOOT_TIME_PAGE_SIZE
> +#define SECTION_SIZE_BITS	29
> +#else
>  #define SECTION_SIZE_BITS	(PAGE_SIZE == SZ_64K ? 29 : 27)
> +#endif
> 
>  #endif
> diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
> index a168f3337446f..9968320f83bc4 100644
> --- a/arch/arm64/kernel/image-vars.h
> +++ b/arch/arm64/kernel/image-vars.h
> @@ -36,6 +36,17 @@ PROVIDE(__pi___memcpy			=
> __pi_memcpy);
>  PROVIDE(__pi___memmove			= __pi_memmove);
>  PROVIDE(__pi___memset			= __pi_memset);
> 
> +#ifdef CONFIG_ARM64_BOOT_TIME_PAGE_SIZE
> +PROVIDE(__pi_ptg_page_shift		= ptg_page_shift);
> +PROVIDE(__pi_ptg_pmd_shift		= ptg_pmd_shift);
> +PROVIDE(__pi_ptg_pud_shift		= ptg_pud_shift);
> +PROVIDE(__pi_ptg_p4d_shift		= ptg_p4d_shift);
> +PROVIDE(__pi_ptg_pgdir_shift		= ptg_pgdir_shift);
> +PROVIDE(__pi_ptg_cont_pte_shift		= ptg_cont_pte_shift);
> +PROVIDE(__pi_ptg_cont_pmd_shift		= ptg_cont_pmd_shift);
> +PROVIDE(__pi_ptg_pgtable_levels		= ptg_pgtable_levels);
> +#endif /* CONFIG_ARM64_BOOT_TIME_PAGE_SIZE */
> +
>  PROVIDE(__pi_id_aa64isar1_override	= id_aa64isar1_override);
>  PROVIDE(__pi_id_aa64isar2_override	= id_aa64isar2_override);
>  PROVIDE(__pi_id_aa64mmfr0_override	= id_aa64mmfr0_override);
> diff --git a/arch/arm64/kernel/image.h b/arch/arm64/kernel/image.h
> index 7bc3ba8979019..01502fc3b891b 100644
> --- a/arch/arm64/kernel/image.h
> +++ b/arch/arm64/kernel/image.h
> @@ -47,7 +47,11 @@
>  #define __HEAD_FLAG_BE		ARM64_IMAGE_FLAG_LE
>  #endif
> 
> +#ifdef CONFIG_ARM64_BOOT_TIME_PAGE_SIZE
> +#define __HEAD_FLAG_PAGE_SIZE	0
> +#else
>  #define __HEAD_FLAG_PAGE_SIZE	((PAGE_SHIFT - 10) / 2)
> +#endif
> 
>  #define __HEAD_FLAG_PHYS_BASE	1
> 
> diff --git a/arch/arm64/kernel/pi/map_kernel.c b/arch/arm64/kernel/pi/map_kernel.c
> index deb8cd50b0b0c..22b3c70e04f9c 100644
> --- a/arch/arm64/kernel/pi/map_kernel.c
> +++ b/arch/arm64/kernel/pi/map_kernel.c
> @@ -221,6 +221,49 @@ static void __init map_fdt(u64 fdt, int page_shift)
>  	dsb(ishst);
>  }
> 
> +#ifdef CONFIG_ARM64_BOOT_TIME_PAGE_SIZE
> +static void __init ptg_init(int page_shift)
> +{
> +	ptg_pgtable_levels =
> +		__ARM64_HW_PGTABLE_LEVELS(page_shift,
> CONFIG_ARM64_VA_BITS);
> +
> +	ptg_pgdir_shift = __ARM64_HW_PGTABLE_LEVEL_SHIFT(page_shift,
> +				4 - ptg_pgtable_levels);
> +
> +	ptg_p4d_shift = ptg_pgtable_levels >= 5 ?
> +				__ARM64_HW_PGTABLE_LEVEL_SHIFT(page_shift, 0) :
> +				ptg_pgdir_shift;
> +
> +	ptg_pud_shift = ptg_pgtable_levels >= 4 ?
> +				__ARM64_HW_PGTABLE_LEVEL_SHIFT(page_shift, 1) :
> +				ptg_pgdir_shift;
> +
> +	ptg_pmd_shift = ptg_pgtable_levels >= 3 ?
> +				__ARM64_HW_PGTABLE_LEVEL_SHIFT(page_shift, 2) :
> +				ptg_pgdir_shift;
> +
> +	ptg_page_shift = page_shift;
> +
> +	switch (page_shift) {
> +	case ARM64_PAGE_SHIFT_64K:
> +		ptg_cont_pte_shift = ptg_page_shift + 5;
> +		ptg_cont_pmd_shift = ptg_pmd_shift + 5;
> +		break;
> +	case ARM64_PAGE_SHIFT_16K:
> +		ptg_cont_pte_shift = ptg_page_shift + 7;
> +		ptg_cont_pmd_shift = ptg_pmd_shift + 5;
> +		break;
> +	default: /* ARM64_PAGE_SHIFT_4K */
> +		ptg_cont_pte_shift = ptg_page_shift + 4;
> +		ptg_cont_pmd_shift = ptg_pmd_shift + 4;
> +	}
> +}
> +#else /* CONFIG_ARM64_BOOT_TIME_PAGE_SIZE */
> +static inline void ptg_init(int page_shift)
> +{
> +}
> +#endif /* CONFIG_ARM64_BOOT_TIME_PAGE_SIZE */
> +
>  asmlinkage void __init early_map_kernel(u64 boot_status, void *fdt)
>  {
>  	static char const chosen_str[] __initconst = "/chosen";
> @@ -247,6 +290,8 @@ asmlinkage void __init early_map_kernel(u64 boot_status, void
> *fdt)
>  	if (!page_shift)
>  		page_shift = early_page_shift;
> 
> +	ptg_init(page_shift);
> +
>  	if (va_bits > 48) {
>  		u64 page_size = early_page_size(page_shift);
> 
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 9bef7638342ef..c835a50b8b768 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -2424,6 +2424,16 @@ static void kvm_hyp_init_symbols(void)
>  	kvm_nvhe_sym(id_aa64smfr0_el1_sys_val) =
> read_sanitised_ftr_reg(SYS_ID_AA64SMFR0_EL1);
>  	kvm_nvhe_sym(__icache_flags) = __icache_flags;
>  	kvm_nvhe_sym(kvm_arm_vmid_bits) = kvm_arm_vmid_bits;
> +#ifdef CONFIG_ARM64_BOOT_TIME_PAGE_SIZE
> +	kvm_nvhe_sym(ptg_page_shift) = ptg_page_shift;
> +	kvm_nvhe_sym(ptg_pmd_shift) = ptg_pmd_shift;
> +	kvm_nvhe_sym(ptg_pud_shift) = ptg_pud_shift;
> +	kvm_nvhe_sym(ptg_p4d_shift) = ptg_p4d_shift;
> +	kvm_nvhe_sym(ptg_pgdir_shift) = ptg_pgdir_shift;
> +	kvm_nvhe_sym(ptg_cont_pte_shift) = ptg_cont_pte_shift;
> +	kvm_nvhe_sym(ptg_cont_pmd_shift) = ptg_cont_pmd_shift;
> +	kvm_nvhe_sym(ptg_pgtable_levels) = ptg_pgtable_levels;
> +#endif /* CONFIG_ARM64_BOOT_TIME_PAGE_SIZE */
>  }
> 
>  static int __init kvm_hyp_init_protection(u32 hyp_va_bits)
> diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile
> b/arch/arm64/kvm/hyp/nvhe/Makefile
> index b43426a493df5..a8fcbb84c7996 100644
> --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> @@ -27,6 +27,7 @@ hyp-obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-
> init.o host.o
>  	 cache.o setup.o mm.o mem_protect.o sys_regs.o pkvm.o stacktrace.o ffa.o
>  hyp-obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
>  	 ../fpsimd.o ../hyp-entry.o ../exception.o ../pgtable.o
> +hyp-obj-$(CONFIG_ARM64_BOOT_TIME_PAGE_SIZE) += pgtable-geometry.o
>  hyp-obj-$(CONFIG_LIST_HARDENED) += list_debug.o
>  hyp-obj-y += $(lib-objs)
> 
> diff --git a/arch/arm64/kvm/hyp/nvhe/pgtable-geometry.c
> b/arch/arm64/kvm/hyp/nvhe/pgtable-geometry.c
> new file mode 100644
> index 0000000000000..17f807450a31a
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/nvhe/pgtable-geometry.c
> @@ -0,0 +1,16 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2024 ARM Ltd.
> + */
> +
> +#include <linux/cache.h>
> +#include <asm/pgtable-geometry.h>
> +
> +int ptg_page_shift __ro_after_init;
> +int ptg_pmd_shift __ro_after_init;
> +int ptg_pud_shift __ro_after_init;
> +int ptg_p4d_shift __ro_after_init;
> +int ptg_pgdir_shift __ro_after_init;
> +int ptg_cont_pte_shift __ro_after_init;
> +int ptg_cont_pmd_shift __ro_after_init;
> +int ptg_pgtable_levels __ro_after_init;
> diff --git a/arch/arm64/mm/Makefile b/arch/arm64/mm/Makefile
> index 60454256945b8..2ba30d06b35fe 100644
> --- a/arch/arm64/mm/Makefile
> +++ b/arch/arm64/mm/Makefile
> @@ -3,6 +3,7 @@ obj-y				:= dma-mapping.o extable.o
> fault.o init.o \
>  				   cache.o copypage.o flush.o \
>  				   ioremap.o mmap.o pgd.o mmu.o \
>  				   context.o proc.o pageattr.o fixmap.o
> +obj-$(CONFIG_ARM64_BOOT_TIME_PAGE_SIZE) += pgtable-geometry.o
>  obj-$(CONFIG_ARM64_CONTPTE)	+= contpte.o
>  obj-$(CONFIG_HUGETLB_PAGE)	+= hugetlbpage.o
>  obj-$(CONFIG_PTDUMP_CORE)	+= ptdump.o
> diff --git a/arch/arm64/mm/pgd.c b/arch/arm64/mm/pgd.c
> index 4b106510358b1..c052d0dcb0c69 100644
> --- a/arch/arm64/mm/pgd.c
> +++ b/arch/arm64/mm/pgd.c
> @@ -21,10 +21,12 @@ static bool pgdir_is_page_size(void)
>  {
>  	if (PGD_SIZE == PAGE_SIZE)
>  		return true;
> -	if (CONFIG_PGTABLE_LEVELS == 4)
> -		return !pgtable_l4_enabled();
> -	if (CONFIG_PGTABLE_LEVELS == 5)
> -		return !pgtable_l5_enabled();
> +	if (!IS_ENABLED(CONFIG_ARM64_BOOT_TIME_PAGE_SIZE)) {
> +		if (CONFIG_PGTABLE_LEVELS == 4)
> +			return !pgtable_l4_enabled();
> +		if (CONFIG_PGTABLE_LEVELS == 5)
> +			return !pgtable_l5_enabled();
> +	}
>  	return false;
>  }
> 
> diff --git a/arch/arm64/mm/pgtable-geometry.c b/arch/arm64/mm/pgtable-
> geometry.c
> new file mode 100644
> index 0000000000000..ba50637f1e9d0
> --- /dev/null
> +++ b/arch/arm64/mm/pgtable-geometry.c
> @@ -0,0 +1,24 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2024 ARM Ltd.
> + */
> +
> +#include <linux/cache.h>
> +#include <asm/pgtable-geometry.h>
> +
> +/*
> + * TODO: These should be __ro_after_init, but we need to write to them from the
> + * pi code where they are mapped in the early page table as read-only.
> + * __ro_after_init doesn't become writable until later when the swapper pgtable
> + * is fully set up. We should update the early page table to map __ro_after_init
> + * as read-write.
> + */
> +
> +int ptg_page_shift __read_mostly;
> +int ptg_pmd_shift __read_mostly;

I found that ptg_page_shift and ptg_pmd_shift need
EXPORT_SYMBOL_GPL for cases where code compiled
as a module is using PAGE_SIZE/PAGE_SHIFT or
PMD_SIZE/PMD_SHIFT. Some of the others below
might also need EXPORT_SYMBOL_GPL.

Michael

> +int ptg_pud_shift __read_mostly;
> +int ptg_p4d_shift __read_mostly;
> +int ptg_pgdir_shift __read_mostly;
> +int ptg_cont_pte_shift __read_mostly;
> +int ptg_cont_pmd_shift __read_mostly;
> +int ptg_pgtable_levels __read_mostly;
> diff --git a/drivers/firmware/efi/libstub/arm64.c
> b/drivers/firmware/efi/libstub/arm64.c
> index e57cd3de0a00f..8db9dba7d5423 100644
> --- a/drivers/firmware/efi/libstub/arm64.c
> +++ b/drivers/firmware/efi/libstub/arm64.c
> @@ -68,7 +68,8 @@ efi_status_t check_platform_features(void)
>  		efi_novamap = true;
> 
>  	/* UEFI mandates support for 4 KB granularity, no need to check */
> -	if (IS_ENABLED(CONFIG_ARM64_4K_PAGES))
> +	if (IS_ENABLED(CONFIG_ARM64_4K_PAGES) ||
> +	    IS_ENABLED(CONFIG_ARM64_BOOT_TIME_PAGE_SIZE))
>  		return EFI_SUCCESS;
> 
>  	tg = (read_cpuid(ID_AA64MMFR0_EL1) >>
> ID_AA64MMFR0_EL1_TGRAN_SHIFT) & 0xf;
> --
> 2.43.0
>