Commit 18bc7bd5 authored Aug 10, 2016 by Andy Lutomirski Committed by Ingo Molnar Aug 11, 2016

x86/boot: Synchronize trampoline_cr4_features and mmu_cr4_features directly



The initialization process for trampoline_cr4_features and
mmu_cr4_features was confusing.  The intent is for mmu_cr4_features
and *trampoline_cr4_features to stay in sync, but
trampoline_cr4_features is NULL until setup_real_mode() runs.  The
old code synchronized *trampoline_cr4_features *twice*, once in
setup_real_mode() and once in setup_arch().  It also initialized
mmu_cr4_features in setup_real_mode(), which causes the actual value
of mmu_cr4_features to potentially depend on when setup_real_mode()
is called.

With this patch, mmu_cr4_features is initialized directly in
setup_arch(), and *trampoline_cr4_features is synchronized to
mmu_cr4_features when the trampoline is set up.

After this patch, it should be safe to defer setup_real_mode().

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mario Limonciello <mario_limonciello@dell.com>
Cc: Matt Fleming <mfleming@suse.de>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/d48a263f9912389b957dd495a7127b009259ffe0.1470821230.git.luto@kernel.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 007b7560

arch/x86/kernel/setup.c

+10 −7

Original line number	Diff line number	Diff line
		@@ -1131,6 +1131,16 @@ void __init setup_arch(char **cmdline_p)

		early_trap_pf_init();

		/*
		* Update mmu_cr4_features (and, indirectly, trampoline_cr4_features)
		* with the current CR4 value. This may not be necessary, but
		* auditing all the early-boot CR4 manipulation would be needed to
		* rule it out.
		*/
		if (boot_cpu_data.cpuid_level >= 0)
		/* A CPU has %cr4 if and only if it has CPUID. */
		mmu_cr4_features = __read_cr4();

		setup_real_mode();

		memblock_set_current_limit(get_max_mapped());
		@@ -1180,13 +1190,6 @@ void __init setup_arch(char **cmdline_p)

		kasan_init();

		if (boot_cpu_data.cpuid_level >= 0) {
		/* A CPU has %cr4 if and only if it has CPUID */
		mmu_cr4_features = __read_cr4();
		if (trampoline_cr4_features)
		*trampoline_cr4_features = mmu_cr4_features;
		}

		#ifdef CONFIG_X86_32
		/* sync back kernel address range */
		clone_pgd_range(initial_page_table + KERNEL_PGD_BOUNDARY,

arch/x86/realmode/init.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -4,6 +4,7 @@
		#include <asm/cacheflush.h>
		#include <asm/pgtable.h>
		#include <asm/realmode.h>
		#include <asm/tlbflush.h>

		struct real_mode_header *real_mode_header;
		u32 *trampoline_cr4_features;
		@@ -84,7 +85,7 @@ void __init setup_real_mode(void)

		trampoline_header->start = (u64) secondary_startup_64;
		trampoline_cr4_features = &trampoline_header->cr4;
		*trampoline_cr4_features = __read_cr4();
		*trampoline_cr4_features = mmu_cr4_features;

		trampoline_pgd = (u64 *) __va(real_mode_header->trampoline_pgd);
		trampoline_pgd[0] = trampoline_pgd_entry.pgd;