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

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Message-ID: <oqdepd27wqf4duawnb3qo2ra6ftjyzjqfxupfj3hkmxvp6w4tl@oy32plygk7dt>
Date: Fri, 16 May 2025 14:09:28 +0300
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Jürgen Groß <jgross@...e.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, 
	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>, Ard Biesheuvel <ardb@...nel.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>, 
	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, May 16, 2025 at 12:42:21PM +0200, Jürgen Groß wrote:
> On 16.05.25 11:15, Kirill A. Shutemov 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>
> > ---
> >   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(-)
> 
> There are some instances of:
> 
> #if CONFIG_PGTABLE_LEVELS >= 5
> 
> in 64-bit-only code under arch/x86, which could be simplified, too.
> 
> They are still correct, but I wanted to hint at further code removals
> being possible.

Okay, fair enough. Fixup is below.

Did I miss anything else?

diff --git a/arch/x86/entry/vsyscall/vsyscall_64.c b/arch/x86/entry/vsyscall/vsyscall_64.c
index 2fb7d53cf333..c9103a6fa06e 100644
--- a/arch/x86/entry/vsyscall/vsyscall_64.c
+++ b/arch/x86/entry/vsyscall/vsyscall_64.c
@@ -341,9 +341,7 @@ void __init set_vsyscall_pgtable_user_bits(pgd_t *root)
 	pgd = pgd_offset_pgd(root, VSYSCALL_ADDR);
 	set_pgd(pgd, __pgd(pgd_val(*pgd) | _PAGE_USER));
 	p4d = p4d_offset(pgd, VSYSCALL_ADDR);
-#if CONFIG_PGTABLE_LEVELS >= 5
 	set_p4d(p4d, __p4d(p4d_val(*p4d) | _PAGE_USER));
-#endif
 	pud = pud_offset(p4d, VSYSCALL_ADDR);
 	set_pud(pud, __pud(pud_val(*pud) | _PAGE_USER));
 	pmd = pmd_offset(pud, VSYSCALL_ADDR);
diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
index b89f8f1194a9..f06e5d6a2747 100644
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -41,11 +41,9 @@ static inline void sync_initial_page_table(void) { }
 	pr_err("%s:%d: bad pud %p(%016lx)\n",		\
 	       __FILE__, __LINE__, &(e), pud_val(e))
 
-#if CONFIG_PGTABLE_LEVELS >= 5
 #define p4d_ERROR(e)					\
 	pr_err("%s:%d: bad p4d %p(%016lx)\n",		\
 	       __FILE__, __LINE__, &(e), p4d_val(e))
-#endif
 
 #define pgd_ERROR(e)					\
 	pr_err("%s:%d: bad pgd %p(%016lx)\n",		\
diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
index 38971c6dcd4b..61c52bb80e33 100644
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -578,7 +578,6 @@ static void xen_set_p4d(p4d_t *ptr, p4d_t val)
 	xen_mc_issue(XEN_LAZY_MMU);
 }
 
-#if CONFIG_PGTABLE_LEVELS >= 5
 __visible p4dval_t xen_p4d_val(p4d_t p4d)
 {
 	return pte_mfn_to_pfn(p4d.p4d);
@@ -592,7 +591,6 @@ __visible p4d_t xen_make_p4d(p4dval_t p4d)
 	return native_make_p4d(p4d);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_make_p4d);
-#endif  /* CONFIG_PGTABLE_LEVELS >= 5 */
 
 static void xen_pmd_walk(struct mm_struct *mm, pmd_t *pmd,
 			 void (*func)(struct mm_struct *mm, struct page *,
-- 
  Kiryl Shutsemau / Kirill A. Shutemov