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Message-ID: <CAMj1kXGq54gGY+ogeEsq8NuP+FKhqJsk06D3K=HUnvunWkFJOg@mail.gmail.com>
Date: Fri, 16 May 2025 10:54:16 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>, Jonathan Corbet <corbet@....net>, Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>, Jan Kiszka <jan.kiszka@...mens.com>,
Kieran Bingham <kbingham@...nel.org>, Michael Roth <michael.roth@....com>,
Rick Edgecombe <rick.p.edgecombe@...el.com>, Brijesh Singh <brijesh.singh@....com>,
Sandipan Das <sandipan.das@....com>, Juergen Gross <jgross@...e.com>,
Tom Lendacky <thomas.lendacky@....com>, linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org, linux-efi@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv2 3/3] x86/64/mm: Make 5-level paging support unconditional
On Fri, 16 May 2025 at 10:15, Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
>
> Both Intel and AMD CPUs support 5-level paging, which is expected to
> become more widely adopted in the future.
>
> Remove CONFIG_X86_5LEVEL and ifdeffery for it to make it more readable.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Suggested-by: Borislav Petkov <bp@...en8.de>
This will conflict with my changes, but I agree with them in principle so
Reviewed-by: Ard Biesheuvel <ardb@...nel.org>
> ---
> Documentation/arch/x86/cpuinfo.rst | 8 +++----
> .../arch/x86/x86_64/5level-paging.rst | 9 --------
> arch/x86/Kconfig | 22 +------------------
> arch/x86/Kconfig.cpufeatures | 4 ----
> arch/x86/boot/compressed/pgtable_64.c | 11 ++--------
> arch/x86/boot/header.S | 4 ----
> arch/x86/boot/startup/map_kernel.c | 5 +----
> arch/x86/include/asm/page_64.h | 2 --
> arch/x86/include/asm/page_64_types.h | 7 ------
> arch/x86/include/asm/pgtable_64_types.h | 18 ---------------
> arch/x86/kernel/alternative.c | 2 +-
> arch/x86/kernel/head64.c | 2 --
> arch/x86/kernel/head_64.S | 2 --
> arch/x86/mm/init.c | 4 ----
> arch/x86/mm/pgtable.c | 2 +-
> drivers/firmware/efi/libstub/x86-5lvl.c | 2 +-
> 16 files changed, 10 insertions(+), 94 deletions(-)
>
> diff --git a/Documentation/arch/x86/cpuinfo.rst b/Documentation/arch/x86/cpuinfo.rst
> index f80e2a558d2a..dd8b7806944e 100644
> --- a/Documentation/arch/x86/cpuinfo.rst
> +++ b/Documentation/arch/x86/cpuinfo.rst
> @@ -173,10 +173,10 @@ For example, when an old kernel is running on new hardware.
> The kernel disabled support for it at compile-time
> --------------------------------------------------
>
> -For example, if 5-level-paging is not enabled when building (i.e.,
> -CONFIG_X86_5LEVEL is not selected) the flag "la57" will not show up [#f1]_.
> +For example, if Linear Address Masking (LAM) is not enabled when building (i.e.,
> +CONFIG_ADDRESS_MASKING is not selected) the flag "lam" will not show up.
> Even though the feature will still be detected via CPUID, the kernel disables
> -it by clearing via setup_clear_cpu_cap(X86_FEATURE_LA57).
> +it by clearing via setup_clear_cpu_cap(X86_FEATURE_LAM).
>
> The feature is disabled at boot-time
> ------------------------------------
> @@ -200,5 +200,3 @@ missing at runtime. For example, AVX flags will not show up if XSAVE feature
> is disabled since they depend on XSAVE feature. Another example would be broken
> CPUs and them missing microcode patches. Due to that, the kernel decides not to
> enable a feature.
> -
> -.. [#f1] 5-level paging uses linear address of 57 bits.
> diff --git a/Documentation/arch/x86/x86_64/5level-paging.rst b/Documentation/arch/x86/x86_64/5level-paging.rst
> index 71f882f4a173..ad7ddc13f79d 100644
> --- a/Documentation/arch/x86/x86_64/5level-paging.rst
> +++ b/Documentation/arch/x86/x86_64/5level-paging.rst
> @@ -22,15 +22,6 @@ QEMU 2.9 and later support 5-level paging.
> Virtual memory layout for 5-level paging is described in
> Documentation/arch/x86/x86_64/mm.rst
>
> -
> -Enabling 5-level paging
> -=======================
> -CONFIG_X86_5LEVEL=y enables the feature.
> -
> -Kernel with CONFIG_X86_5LEVEL=y still able to boot on 4-level hardware.
> -In this case additional page table level -- p4d -- will be folded at
> -runtime.
> -
> User-space and large virtual address space
> ==========================================
> On x86, 5-level paging enables 56-bit userspace virtual address space.
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 45b36a019b5e..7aed3fa0e780 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -427,8 +427,7 @@ config DYNAMIC_PHYSICAL_MASK
>
> config PGTABLE_LEVELS
> int
> - default 5 if X86_5LEVEL
> - default 4 if X86_64
> + default 5 if X86_64
> default 3 if X86_PAE
> default 2
>
> @@ -1464,25 +1463,6 @@ config X86_PAE
> has the cost of more pagetable lookup overhead, and also
> consumes more pagetable space per process.
>
> -config X86_5LEVEL
> - bool "Enable 5-level page tables support"
> - default y
> - depends on X86_64
> - help
> - 5-level paging enables access to larger address space:
> - up to 128 PiB of virtual address space and 4 PiB of
> - physical address space.
> -
> - It will be supported by future Intel CPUs.
> -
> - A kernel with the option enabled can be booted on machines that
> - support 4- or 5-level paging.
> -
> - See Documentation/arch/x86/x86_64/5level-paging.rst for more
> - information.
> -
> - Say N if unsure.
> -
> config X86_DIRECT_GBPAGES
> def_bool y
> depends on X86_64
> diff --git a/arch/x86/Kconfig.cpufeatures b/arch/x86/Kconfig.cpufeatures
> index e12d5b7e39a2..250c10627ab3 100644
> --- a/arch/x86/Kconfig.cpufeatures
> +++ b/arch/x86/Kconfig.cpufeatures
> @@ -132,10 +132,6 @@ config X86_DISABLED_FEATURE_OSPKE
> def_bool y
> depends on !X86_INTEL_MEMORY_PROTECTION_KEYS
>
> -config X86_DISABLED_FEATURE_LA57
> - def_bool y
> - depends on !X86_5LEVEL
> -
> config X86_DISABLED_FEATURE_PTI
> def_bool y
> depends on !MITIGATION_PAGE_TABLE_ISOLATION
> diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
> index 5a6c7a190e5b..bdd26050dff7 100644
> --- a/arch/x86/boot/compressed/pgtable_64.c
> +++ b/arch/x86/boot/compressed/pgtable_64.c
> @@ -10,12 +10,10 @@
> #define BIOS_START_MIN 0x20000U /* 128K, less than this is insane */
> #define BIOS_START_MAX 0x9f000U /* 640K, absolute maximum */
>
> -#ifdef CONFIG_X86_5LEVEL
> /* __pgtable_l5_enabled needs to be in .data to avoid being cleared along with .bss */
> unsigned int __section(".data") __pgtable_l5_enabled;
> unsigned int __section(".data") pgdir_shift = 39;
> unsigned int __section(".data") ptrs_per_p4d = 1;
> -#endif
>
> /* Buffer to preserve trampoline memory */
> static char trampoline_save[TRAMPOLINE_32BIT_SIZE];
> @@ -114,18 +112,13 @@ asmlinkage void configure_5level_paging(struct boot_params *bp, void *pgtable)
> * Check if LA57 is desired and supported.
> *
> * There are several parts to the check:
> - * - if the kernel supports 5-level paging: CONFIG_X86_5LEVEL=y
> * - if user asked to disable 5-level paging: no5lvl in cmdline
> * - if the machine supports 5-level paging:
> * + CPUID leaf 7 is supported
> * + the leaf has the feature bit set
> - *
> - * That's substitute for boot_cpu_has() in early boot code.
> */
> - if (IS_ENABLED(CONFIG_X86_5LEVEL) &&
> - !cmdline_find_option_bool("no5lvl") &&
> - native_cpuid_eax(0) >= 7 &&
> - (native_cpuid_ecx(7) & (1 << (X86_FEATURE_LA57 & 31)))) {
> + if (!cmdline_find_option_bool("no5lvl") &&
> + native_cpuid_eax(0) >= 7 && (native_cpuid_ecx(7) & BIT(16))) {
> l5_required = true;
>
> /* Initialize variables for 5-level paging */
> diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
> index 9cb91421b4e4..e30649e44d8f 100644
> --- a/arch/x86/boot/header.S
> +++ b/arch/x86/boot/header.S
> @@ -361,12 +361,8 @@ xloadflags:
> #endif
>
> #ifdef CONFIG_X86_64
> -#ifdef CONFIG_X86_5LEVEL
> #define XLF56 (XLF_5LEVEL|XLF_5LEVEL_ENABLED)
> #else
> -#define XLF56 XLF_5LEVEL
> -#endif
> -#else
> #define XLF56 0
> #endif
>
> diff --git a/arch/x86/boot/startup/map_kernel.c b/arch/x86/boot/startup/map_kernel.c
> index 905e8734b5a3..332dbe6688c4 100644
> --- a/arch/x86/boot/startup/map_kernel.c
> +++ b/arch/x86/boot/startup/map_kernel.c
> @@ -16,9 +16,6 @@ extern unsigned int next_early_pgt;
>
> static inline bool check_la57_support(void)
> {
> - if (!IS_ENABLED(CONFIG_X86_5LEVEL))
> - return false;
> -
> /*
> * 5-level paging is detected and enabled at kernel decompression
> * stage. Only check if it has been enabled there.
> @@ -129,7 +126,7 @@ unsigned long __head __startup_64(unsigned long p2v_offset,
> pgd = rip_rel_ptr(early_top_pgt);
> pgd[pgd_index(__START_KERNEL_map)] += load_delta;
>
> - if (IS_ENABLED(CONFIG_X86_5LEVEL) && la57) {
> + if (la57) {
> p4d = (p4dval_t *)rip_rel_ptr(level4_kernel_pgt);
> p4d[MAX_PTRS_PER_P4D - 1] += load_delta;
>
> diff --git a/arch/x86/include/asm/page_64.h b/arch/x86/include/asm/page_64.h
> index d3aab6f4e59a..015d23f3e01f 100644
> --- a/arch/x86/include/asm/page_64.h
> +++ b/arch/x86/include/asm/page_64.h
> @@ -62,7 +62,6 @@ static inline void clear_page(void *page)
> void copy_page(void *to, void *from);
> KCFI_REFERENCE(copy_page);
>
> -#ifdef CONFIG_X86_5LEVEL
> /*
> * User space process size. This is the first address outside the user range.
> * There are a few constraints that determine this:
> @@ -93,7 +92,6 @@ static __always_inline unsigned long task_size_max(void)
>
> return ret;
> }
> -#endif /* CONFIG_X86_5LEVEL */
>
> #endif /* !__ASSEMBLER__ */
>
> diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
> index 6b8c8169c71d..7400dab373fe 100644
> --- a/arch/x86/include/asm/page_64_types.h
> +++ b/arch/x86/include/asm/page_64_types.h
> @@ -48,14 +48,7 @@
> /* See Documentation/arch/x86/x86_64/mm.rst for a description of the memory map. */
>
> #define __PHYSICAL_MASK_SHIFT 52
> -
> -#ifdef CONFIG_X86_5LEVEL
> #define __VIRTUAL_MASK_SHIFT (pgtable_l5_enabled() ? 56 : 47)
> -/* See task_size_max() in <asm/page_64.h> */
> -#else
> -#define __VIRTUAL_MASK_SHIFT 47
> -#define task_size_max() ((_AC(1,UL) << __VIRTUAL_MASK_SHIFT) - PAGE_SIZE)
> -#endif
>
> #define TASK_SIZE_MAX task_size_max()
> #define DEFAULT_MAP_WINDOW ((1UL << 47) - PAGE_SIZE)
> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> index eee06f77b245..4604f924d8b8 100644
> --- a/arch/x86/include/asm/pgtable_64_types.h
> +++ b/arch/x86/include/asm/pgtable_64_types.h
> @@ -23,7 +23,6 @@ typedef struct { pmdval_t pmd; } pmd_t;
>
> extern unsigned int __pgtable_l5_enabled;
>
> -#ifdef CONFIG_X86_5LEVEL
> #ifdef USE_EARLY_PGTABLE_L5
> /*
> * cpu_feature_enabled() is not available in early boot code.
> @@ -37,17 +36,11 @@ static inline bool pgtable_l5_enabled(void)
> #define pgtable_l5_enabled() cpu_feature_enabled(X86_FEATURE_LA57)
> #endif /* USE_EARLY_PGTABLE_L5 */
>
> -#else
> -#define pgtable_l5_enabled() 0
> -#endif /* CONFIG_X86_5LEVEL */
> -
> extern unsigned int pgdir_shift;
> extern unsigned int ptrs_per_p4d;
>
> #endif /* !__ASSEMBLER__ */
>
> -#ifdef CONFIG_X86_5LEVEL
> -
> /*
> * PGDIR_SHIFT determines what a top-level page table entry can map
> */
> @@ -65,17 +58,6 @@ extern unsigned int ptrs_per_p4d;
>
> #define MAX_POSSIBLE_PHYSMEM_BITS 52
>
> -#else /* CONFIG_X86_5LEVEL */
> -
> -/*
> - * PGDIR_SHIFT determines what a top-level page table entry can map
> - */
> -#define PGDIR_SHIFT 39
> -#define PTRS_PER_PGD 512
> -#define MAX_PTRS_PER_P4D 1
> -
> -#endif /* CONFIG_X86_5LEVEL */
> -
> /*
> * 3rd level page
> */
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index 29572927f9c5..ecfe7b497cad 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -596,7 +596,7 @@ void __init_or_module noinline apply_alternatives(struct alt_instr *start,
> DPRINTK(ALT, "alt table %px, -> %px", start, end);
>
> /*
> - * In the case CONFIG_X86_5LEVEL=y, KASAN_SHADOW_START is defined using
> + * KASAN_SHADOW_START is defined using
> * cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here.
> * During the process, KASAN becomes confused seeing partial LA57
> * conversion and triggers a false-positive out-of-bound report.
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index 9f617be64fa9..533fcf5636fc 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -51,13 +51,11 @@ unsigned int __initdata next_early_pgt;
> SYM_PIC_ALIAS(next_early_pgt);
> pmdval_t early_pmd_flags = __PAGE_KERNEL_LARGE & ~(_PAGE_GLOBAL | _PAGE_NX);
>
> -#ifdef CONFIG_X86_5LEVEL
> unsigned int __pgtable_l5_enabled __ro_after_init;
> unsigned int pgdir_shift __ro_after_init = 39;
> EXPORT_SYMBOL(pgdir_shift);
> unsigned int ptrs_per_p4d __ro_after_init = 1;
> EXPORT_SYMBOL(ptrs_per_p4d);
> -#endif
>
> unsigned long page_offset_base __ro_after_init = __PAGE_OFFSET_BASE_L4;
> EXPORT_SYMBOL(page_offset_base);
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index 069420853304..3e9b3a3bd039 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -649,13 +649,11 @@ SYM_DATA_START_PTI_ALIGNED(init_top_pgt)
> SYM_DATA_END(init_top_pgt)
> #endif
>
> -#ifdef CONFIG_X86_5LEVEL
> SYM_DATA_START_PAGE_ALIGNED(level4_kernel_pgt)
> .fill 511,8,0
> .quad level3_kernel_pgt - __START_KERNEL_map + _PAGE_TABLE_NOENC
> SYM_DATA_END(level4_kernel_pgt)
> SYM_PIC_ALIAS(level4_kernel_pgt)
> -#endif
>
> SYM_DATA_START_PAGE_ALIGNED(level3_kernel_pgt)
> .fill L3_START_KERNEL,8,0
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index aa56d9ac0b8f..7456df985d96 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -174,11 +174,7 @@ __ref void *alloc_low_pages(unsigned int num)
> * randomization is enabled.
> */
>
> -#ifndef CONFIG_X86_5LEVEL
> -#define INIT_PGD_PAGE_TABLES 3
> -#else
> #define INIT_PGD_PAGE_TABLES 4
> -#endif
>
> #ifndef CONFIG_RANDOMIZE_MEMORY
> #define INIT_PGD_PAGE_COUNT (2 * INIT_PGD_PAGE_TABLES)
> diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
> index 59c42dec7076..62777ba4de1a 100644
> --- a/arch/x86/mm/pgtable.c
> +++ b/arch/x86/mm/pgtable.c
> @@ -592,7 +592,7 @@ void native_set_fixmap(unsigned /* enum fixed_addresses */ idx,
> }
>
> #ifdef CONFIG_HAVE_ARCH_HUGE_VMAP
> -#ifdef CONFIG_X86_5LEVEL
> +#if CONFIG_PGTABLE_LEVELS > 4
> /**
> * p4d_set_huge - Set up kernel P4D mapping
> * @p4d: Pointer to the P4D entry
> diff --git a/drivers/firmware/efi/libstub/x86-5lvl.c b/drivers/firmware/efi/libstub/x86-5lvl.c
> index 77359e802181..f1c5fb45d5f7 100644
> --- a/drivers/firmware/efi/libstub/x86-5lvl.c
> +++ b/drivers/firmware/efi/libstub/x86-5lvl.c
> @@ -62,7 +62,7 @@ efi_status_t efi_setup_5level_paging(void)
>
> void efi_5level_switch(void)
> {
> - bool want_la57 = IS_ENABLED(CONFIG_X86_5LEVEL) && !efi_no5lvl;
> + bool want_la57 = !efi_no5lvl;
> bool have_la57 = native_read_cr4() & X86_CR4_LA57;
> bool need_toggle = want_la57 ^ have_la57;
> u64 *pgt = (void *)la57_toggle + PAGE_SIZE;
> --
> 2.47.2
>
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