[RFC PATCH] x86: Remove CONFIG_DOUBLEFAULT

[Borislav Petkov <bp@alien8.de>]

On Wed, Nov 27, 2019 at 08:19:29AM -0000, tip-bot2 for Andy Lutomirski wrote:
> The following commit has been merged into the x86/urgent branch of tip:
> 
> Commit-ID:     93efbde2c331004d8053f04b4bf0ca3e630b474a
> Gitweb:        https://git.kernel.org/tip/93efbde2c331004d8053f04b4bf0ca3e630b474a
> Author:        Andy Lutomirski <luto@kernel.org>
> AuthorDate:    Wed, 20 Nov 2019 22:12:38 -08:00
> Committer:     Ingo Molnar <mingo@kernel.org>
> CommitterDate: Tue, 26 Nov 2019 21:53:34 +01:00
> 
> x86/traps: Disentangle the 32-bit and 64-bit doublefault code
> 
> The 64-bit doublefault handler is much nicer than the 32-bit one.
> As a first step toward unifying them, make the 64-bit handler
> self-contained.  This should have no effect no functional effect
> except in the odd case of x86_64 with CONFIG_DOUBLEFAULT=n in which
> case it will change the logging a bit.
> 
> This also gets rid of CONFIG_DOUBLEFAULT configurability on 64-bit
> kernels.  It didn't do anything useful -- CONFIG_DOUBLEFAULT=n
> didn't actually disable doublefault handling on x86_64.
> 
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> ---
>  arch/x86/Kconfig.debug           |  2 +-
>  arch/x86/include/asm/processor.h |  1 -
>  arch/x86/kernel/doublefault.c    | 11 -----------
>  arch/x86/kernel/traps.c          | 12 +++---------
>  4 files changed, 4 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
> index 409c00f..c4eab8e 100644
> --- a/arch/x86/Kconfig.debug
> +++ b/arch/x86/Kconfig.debug
> @@ -117,7 +117,7 @@ config DEBUG_WX
>  
>  config DOUBLEFAULT
>  	default y
> -	bool "Enable doublefault exception handler" if EXPERT
> +	bool "Enable doublefault exception handler" if EXPERT && X86_32

Yeah, how about we simplify the whole df code even more. It is clearly
much better to always have a registered #DF handler so let's get rid of
that silly config option.

Only compile-tested.

---
From: Borislav Petkov <bp@suse.de>
Date: Wed, 27 Nov 2019 19:12:29 +0100
Subject: [RFC PATCH] x86: Remove CONFIG_DOUBLEFAULT

... and make it unconditional.

Signed-off-by: Borislav Petkov <bp@suse.de>
---
 arch/x86/Kconfig.debug             | 9 ---------
 arch/x86/entry/entry_32.S          | 2 --
 arch/x86/include/asm/doublefault.h | 6 ++----
 arch/x86/include/asm/traps.h       | 2 --
 arch/x86/kernel/Makefile           | 4 +---
 arch/x86/kernel/dumpstack_32.c     | 4 ----
 arch/x86/kernel/traps.c            | 2 --
 arch/x86/mm/cpu_entry_area.c       | 4 +---
 8 files changed, 4 insertions(+), 29 deletions(-)

diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug
index c4eab8ed33a3..f386068114d6 100644
--- a/arch/x86/Kconfig.debug
+++ b/arch/x86/Kconfig.debug
@@ -115,15 +115,6 @@ config DEBUG_WX
 
 	  If in doubt, say "Y".
 
-config DOUBLEFAULT
-	default y
-	bool "Enable doublefault exception handler" if EXPERT && X86_32
-	---help---
-	  This option allows trapping of rare doublefault exceptions that
-	  would otherwise cause a system to silently reboot. Disabling this
-	  option saves about 4k and might cause you much additional grey
-	  hair.
-
 config DEBUG_TLBFLUSH
 	bool "Set upper limit of TLB entries to flush one-by-one"
 	depends on DEBUG_KERNEL
diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 7e0560442538..8bd285617c21 100644
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -1536,7 +1536,6 @@ SYM_CODE_START(debug)
 	jmp	common_exception
 SYM_CODE_END(debug)
 
-#ifdef CONFIG_DOUBLEFAULT
 SYM_CODE_START(double_fault)
 1:
 	/*
@@ -1576,7 +1575,6 @@ SYM_CODE_START(double_fault)
 	hlt
 	jmp 1b
 SYM_CODE_END(double_fault)
-#endif
 
 /*
  * NMI is doubly nasty.  It can happen on the first instruction of
diff --git a/arch/x86/include/asm/doublefault.h b/arch/x86/include/asm/doublefault.h
index af9a14ac8962..65b58363797e 100644
--- a/arch/x86/include/asm/doublefault.h
+++ b/arch/x86/include/asm/doublefault.h
@@ -2,12 +2,10 @@
 #ifndef _ASM_X86_DOUBLEFAULT_H
 #define _ASM_X86_DOUBLEFAULT_H
 
-#if defined(CONFIG_X86_32) && defined(CONFIG_DOUBLEFAULT)
+#ifdef CONFIG_X86_32
 extern void doublefault_init_cpu_tss(void);
 #else
-static inline void doublefault_init_cpu_tss(void)
-{
-}
+static inline void doublefault_init_cpu_tss(void) { }
 #endif
 
 #endif /* _ASM_X86_DOUBLEFAULT_H */
diff --git a/arch/x86/include/asm/traps.h b/arch/x86/include/asm/traps.h
index ffa0dc8a535e..4580c8207da3 100644
--- a/arch/x86/include/asm/traps.h
+++ b/arch/x86/include/asm/traps.h
@@ -69,9 +69,7 @@ dotraplinkage void do_overflow(struct pt_regs *regs, long error_code);
 dotraplinkage void do_bounds(struct pt_regs *regs, long error_code);
 dotraplinkage void do_invalid_op(struct pt_regs *regs, long error_code);
 dotraplinkage void do_device_not_available(struct pt_regs *regs, long error_code);
-#if defined(CONFIG_X86_64) || defined(CONFIG_DOUBLEFAULT)
 dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsigned long cr2);
-#endif
 dotraplinkage void do_coprocessor_segment_overrun(struct pt_regs *regs, long error_code);
 dotraplinkage void do_invalid_TSS(struct pt_regs *regs, long error_code);
 dotraplinkage void do_segment_not_present(struct pt_regs *regs, long error_code);
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index ccb13271895d..0f5bdf6dfce6 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -104,9 +104,7 @@ obj-$(CONFIG_KEXEC_FILE)	+= kexec-bzimage64.o
 obj-$(CONFIG_CRASH_DUMP)	+= crash_dump_$(BITS).o
 obj-y				+= kprobes/
 obj-$(CONFIG_MODULES)		+= module.o
-ifeq ($(CONFIG_X86_32),y)
-obj-$(CONFIG_DOUBLEFAULT)	+= doublefault_32.o
-endif
+obj-$(CONFIG_X86_32)		+= doublefault_32.o
 obj-$(CONFIG_KGDB)		+= kgdb.o
 obj-$(CONFIG_VM86)		+= vm86_32.o
 obj-$(CONFIG_EARLY_PRINTK)	+= early_printk.o
diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
index 8e3a8fedfa4d..722fd712e1cf 100644
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -87,7 +87,6 @@ static bool in_softirq_stack(unsigned long *stack, struct stack_info *info)
 
 static bool in_doublefault_stack(unsigned long *stack, struct stack_info *info)
 {
-#ifdef CONFIG_DOUBLEFAULT
 	struct cpu_entry_area *cea = get_cpu_entry_area(raw_smp_processor_id());
 	struct doublefault_stack *ss = &cea->doublefault_stack;
 
@@ -103,9 +102,6 @@ static bool in_doublefault_stack(unsigned long *stack, struct stack_info *info)
 	info->next_sp	= (unsigned long *)this_cpu_read(cpu_tss_rw.x86_tss.sp);
 
 	return true;
-#else
-	return false;
-#endif
 }
 
 
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index f19de6f45d48..3bcbf5c3d1f0 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -306,7 +306,6 @@ __visible void __noreturn handle_stack_overflow(const char *message,
 }
 #endif
 
-#if defined(CONFIG_X86_64) || defined(CONFIG_DOUBLEFAULT)
 /*
  * Runs on an IST stack for x86_64 and on a special task stack for x86_32.
  *
@@ -430,7 +429,6 @@ dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code, unsign
 	die("double fault", regs, error_code);
 	panic("Machine halted.");
 }
-#endif
 
 dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
 {
diff --git a/arch/x86/mm/cpu_entry_area.c b/arch/x86/mm/cpu_entry_area.c
index 56f9189bbadb..5199d8a1daf1 100644
--- a/arch/x86/mm/cpu_entry_area.c
+++ b/arch/x86/mm/cpu_entry_area.c
@@ -17,7 +17,7 @@ static DEFINE_PER_CPU_PAGE_ALIGNED(struct exception_stacks, exception_stacks);
 DEFINE_PER_CPU(struct cea_exception_stacks*, cea_exception_stacks);
 #endif
 
-#if defined(CONFIG_X86_32) && defined(CONFIG_DOUBLEFAULT)
+#ifdef CONFIG_X86_32
 DECLARE_PER_CPU_PAGE_ALIGNED(struct doublefault_stack, doublefault_stack);
 #endif
 
@@ -114,12 +114,10 @@ static void __init percpu_setup_exception_stacks(unsigned int cpu)
 #else
 static inline void percpu_setup_exception_stacks(unsigned int cpu)
 {
-#ifdef CONFIG_DOUBLEFAULT
 	struct cpu_entry_area *cea = get_cpu_entry_area(cpu);
 
 	cea_map_percpu_pages(&cea->doublefault_stack,
 			     &per_cpu(doublefault_stack, cpu), 1, PAGE_KERNEL);
-#endif
 }
 #endif
 
-- 
2.21.0

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette