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Date: Mon, 18 Sep 2017 13:55:50 +0300 From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> To: Ingo Molnar <mingo@...hat.com>, Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Andy Lutomirski <luto@...capital.net>, Cyrill Gorcunov <gorcunov@...nvz.org>, Borislav Petkov <bp@...e.de>, linux-mm@...ck.org, linux-kernel@...r.kernel.org, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com> Subject: [PATCHv7 16/19] x86/mm: Allow to boot without la57 if CONFIG_X86_5LEVEL=y All pieces of the puzzle are in place and we can now allow to boot with CONFIG_X86_5LEVEL=y on a machine without la57 support. Kernel will detect that la57 is missing and fold p4d at runtime. Update documentation and Kconfig option description to reflect the change. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com> --- Documentation/x86/x86_64/5level-paging.txt | 9 +++------ arch/x86/Kconfig | 4 ++-- arch/x86/include/asm/required-features.h | 8 +------- 3 files changed, 6 insertions(+), 15 deletions(-) diff --git a/Documentation/x86/x86_64/5level-paging.txt b/Documentation/x86/x86_64/5level-paging.txt index 087251a0d99c..2432a5ef86d9 100644 --- a/Documentation/x86/x86_64/5level-paging.txt +++ b/Documentation/x86/x86_64/5level-paging.txt @@ -20,12 +20,9 @@ Documentation/x86/x86_64/mm.txt CONFIG_X86_5LEVEL=y enables the feature. -So far, a kernel compiled with the option enabled will be able to boot -only on machines that supports the feature -- see for 'la57' flag in -/proc/cpuinfo. - -The plan is to implement boot-time switching between 4- and 5-level paging -in the future. +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 == diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index f75723d62c25..aaf5c2e00c03 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1411,8 +1411,8 @@ config X86_5LEVEL It will be supported by future Intel CPUs. - Note: a kernel with this option enabled can only be booted - on machines that support the feature. + A kernel with the option enabled can be booted on machines that + support 4- or 5-level paging. See Documentation/x86/x86_64/5level-paging.txt for more information. diff --git a/arch/x86/include/asm/required-features.h b/arch/x86/include/asm/required-features.h index d91ba04dd007..fac9a5c0abe9 100644 --- a/arch/x86/include/asm/required-features.h +++ b/arch/x86/include/asm/required-features.h @@ -53,12 +53,6 @@ # define NEED_MOVBE 0 #endif -#ifdef CONFIG_X86_5LEVEL -# define NEED_LA57 (1<<(X86_FEATURE_LA57 & 31)) -#else -# define NEED_LA57 0 -#endif - #ifdef CONFIG_X86_64 #ifdef CONFIG_PARAVIRT /* Paravirtualized systems may not have PSE or PGE available */ @@ -104,7 +98,7 @@ #define REQUIRED_MASK13 0 #define REQUIRED_MASK14 0 #define REQUIRED_MASK15 0 -#define REQUIRED_MASK16 (NEED_LA57) +#define REQUIRED_MASK16 0 #define REQUIRED_MASK17 0 #define REQUIRED_MASK_CHECK BUILD_BUG_ON_ZERO(NCAPINTS != 18) -- 2.14.1
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