From 18bc7bd523e0fc5be8d76bf84bde733a97a8c375 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 10 Aug 2016 02:29:14 -0700 Subject: [PATCH] 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 Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Mario Limonciello Cc: Matt Fleming Cc: Matthew Garrett Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/d48a263f9912389b957dd495a7127b009259ffe0.1470821230.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/kernel/setup.c | 17 ++++++++++------- arch/x86/realmode/init.c | 3 ++- 2 files changed, 12 insertions(+), 8 deletions(-) diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c index bf780e0..95c8c9c 100644 --- a/arch/x86/kernel/setup.c +++ b/arch/x86/kernel/setup.c @@ -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, diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c index 705e3ff..c5bdc4e 100644 --- a/arch/x86/realmode/init.c +++ b/arch/x86/realmode/init.c @@ -4,6 +4,7 @@ #include #include #include +#include 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; -- 2.7.4