linux-kernel - Re: [PATCHv2 0/3] x86: Make 5-level paging support unconditional for x86-64

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Message-ID: <20250624082305.2351-1-khaliidcaliy@gmail.com>
Date: Tue, 24 Jun 2025 08:23:03 +0000
From: Khalid Ali <khaliidcaliy@...il.com>
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	dave.hansen@...ux.intel.com,
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Subject: Re: [PATCHv2 0/3] x86: Make 5-level paging support unconditional for x86-64

>Both Intel and AMD CPUs support 5-level paging, which is expected to
>become more widely adopted in the future.
>
>Remove CONFIG_X86_5LEVEL.
>
>In preparation to that remove CONFIG_DYNAMIC_MEMORY_LAYOUT and make
>SPARSEMEM_VMEMMAP the only memory model.
>
>v3:
> - Drop few "#if CONFIG_PGTABLE_LEVELS >= 5";
> - Make PARAVIRT_XXL 64-bit explicitly and drop ifdefs
>   to support PGTABLE_LEVELS < 5;
> - Add Reviewed-by tags from Ard;
>v2:
> - Fix 32-bit build by wrapping p4d_set_huge() and p4d_clear_huge() in
>   #if CONFIG_PGTABLE_LEVELS > 4;
> - Rebased onto current tip/master;
>
>Kirill A. Shutemov (4):
>  x86/64/mm: Always use dynamic memory layout
>  x86/64/mm: Make SPARSEMEM_VMEMMAP the only memory model
>  x86/64/mm: Make 5-level paging support unconditional
>  x86/paravirt: Restrict PARAVIRT_XXL to 64-bit only
>
> Documentation/arch/x86/cpuinfo.rst            |  8 ++---
> .../arch/x86/x86_64/5level-paging.rst         |  9 -----
> arch/x86/Kconfig                              | 33 ++-----------------
> 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/entry/vsyscall/vsyscall_64.c         |  2 --
> arch/x86/include/asm/page_64.h                |  2 --
> arch/x86/include/asm/page_64_types.h          | 11 -------
> arch/x86/include/asm/paravirt.h               |  4 ---
> arch/x86/include/asm/paravirt_types.h         |  2 --
> arch/x86/include/asm/pgtable_64.h             |  2 --
> arch/x86/include/asm/pgtable_64_types.h       | 24 --------------
> arch/x86/kernel/alternative.c                 |  2 +-
> arch/x86/kernel/head64.c                      |  4 ---
> arch/x86/kernel/head_64.S                     |  2 --
> arch/x86/kernel/paravirt.c                    |  2 --
> arch/x86/mm/init.c                            |  4 ---
> arch/x86/mm/init_64.c                         |  9 +----
> arch/x86/mm/pgtable.c                         |  2 +-
> arch/x86/xen/mmu_pv.c                         |  4 ---
> drivers/firmware/efi/libstub/x86-5lvl.c       |  2 +-
> scripts/gdb/linux/pgtable.py                  |  4 +--
> 24 files changed, 14 insertions(+), 142 deletions(-)

I think i am too late, however this is completely wrong. There are still processors that doesn't support
5-level paging which is mordern. We may call those processors old, however they are still common and used.

So this patch seem too early for that. Some intel core-i5 and core-i7 doesn't support 5-level paging at all.

This will break x86_64 cpus that doesn't support 5-level paging.