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

Michael Kelley
2024-10-15T17:52:24Z

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
>