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Commit 372fddf7 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Ingo Molnar
Browse files

x86/mm: Introduce the 'no5lvl' kernel parameter 



This kernel parameter allows to force kernel to use 4-level paging even
if hardware and kernel support 5-level paging.

The option may be useful to work around regressions related to 5-level
paging.

Signed-off-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180518103528.59260-5-kirill.shutemov@linux.intel.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent ed7588d5

Documentation/admin-guide/kernel-parameters.txt

+3 −0
Original line number Diff line number Diff line
@@ -2600,6 +2600,9 @@ 
			emulation library even if a 387 maths coprocessor

			is present.



	no5lvl		[X86-64] Disable 5-level paging mode. Forces

			kernel to use 4-level paging instead.



	no_console_suspend

			[HW] Never suspend the console

			Disable suspending of consoles during suspend and

arch/x86/boot/compressed/cmdline.c

+1 −1
Original line number Diff line number Diff line 
// SPDX-License-Identifier: GPL-2.0

#include "misc.h"



#if CONFIG_EARLY_PRINTK || CONFIG_RANDOMIZE_BASE

#if CONFIG_EARLY_PRINTK || CONFIG_RANDOMIZE_BASE || CONFIG_X86_5LEVEL



static unsigned long fs;

static inline void set_fs(unsigned long seg)

arch/x86/boot/compressed/head_64.S

+1 −0
Original line number Diff line number Diff line
@@ -365,6 +365,7 @@ ENTRY(startup_64) 
	 * this function call.

	 */

	pushq	%rsi

	movq	%rsi, %rdi		/* real mode address */

	call	paging_prepare

	popq	%rsi

arch/x86/boot/compressed/pgtable_64.c

+10 −2
Original line number Diff line number Diff line
@@ -31,16 +31,23 @@ static char trampoline_save[TRAMPOLINE_32BIT_SIZE]; 
 */

unsigned long *trampoline_32bit __section(.data);



struct paging_config paging_prepare(void)

extern struct boot_params *boot_params;

int cmdline_find_option_bool(const char *option);



struct paging_config paging_prepare(void *rmode)

{

	struct paging_config paging_config = {};

	unsigned long bios_start, ebda_start;



	/* Initialize boot_params. Required for cmdline_find_option_bool(). */

	boot_params = rmode;



	/*

	 * Check if LA57 is desired and supported.

	 *

	 * There are two parts to the check:

	 * 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
@@ -48,6 +55,7 @@ struct paging_config paging_prepare(void) 
	 * 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)))) {

		paging_config.l5_required = 1;

arch/x86/kernel/cpu/common.c

+15 −0
Original line number Diff line number Diff line
@@ -1028,6 +1028,21 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c) 
	 */

	setup_clear_cpu_cap(X86_FEATURE_PCID);

#endif



	/*

	 * Later in the boot process pgtable_l5_enabled() relies on

	 * cpu_feature_enabled(X86_FEATURE_LA57). If 5-level paging is not

	 * enabled by this point we need to clear the feature bit to avoid

	 * false-positives at the later stage.

	 *

	 * pgtable_l5_enabled() can be false here for several reasons:

	 *  - 5-level paging is disabled compile-time;

	 *  - it's 32-bit kernel;

	 *  - machine doesn't support 5-level paging;

	 *  - user specified 'no5lvl' in kernel command line.

	 */

	if (!pgtable_l5_enabled())

		setup_clear_cpu_cap(X86_FEATURE_LA57);

}



void __init early_cpu_init(void)