kexec: create a new config option CONFIG_KEXEC_FILE for new syscall

Currently new system call kexec_file_load() and all the associated code
compiles if CONFIG_KEXEC=y.  But new syscall also compiles purgatory
code which currently uses gcc option -mcmodel=large.  This option seems
to be available only gcc 4.4 onwards.

Hiding new functionality behind a new config option will not break
existing users of old gcc.  Those who wish to enable new functionality
will require new gcc.  Having said that, I am trying to figure out how
can I move away from using -mcmodel=large but that can take a while.

I think there are other advantages of introducing this new config
option.  As this option will be enabled only on x86_64, other arches
don't have to compile generic kexec code which will never be used.  This
new code selects CRYPTO=y and CRYPTO_SHA256=y.  And all other arches had
to do this for CONFIG_KEXEC.  Now with introduction of new config
option, we can remove crypto dependency from other arches.

Now CONFIG_KEXEC_FILE is available only on x86_64.  So whereever I had
CONFIG_X86_64 defined, I got rid of that.

For CONFIG_KEXEC_FILE, instead of doing select CRYPTO=y, I changed it to
"depends on CRYPTO=y".  This should be safer as "select" is not
recursive.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Tested-by: Shaun Ruffell <sruffell@digium.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

3 files changed, 14 insertions, 5 deletions

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index b5ea75c4a4b4..ada2e2d6be3e 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -71,6 +71,7 @@ obj-$(CONFIG_FTRACE_SYSCALLS)	+= ftrace.o
 obj-$(CONFIG_X86_TSC)		+= trace_clock.o
 obj-$(CONFIG_KEXEC)		+= machine_kexec_$(BITS).o
 obj-$(CONFIG_KEXEC)		+= relocate_kernel_$(BITS).o crash.o
+obj-$(CONFIG_KEXEC_FILE)	+= kexec-bzimage64.o
 obj-$(CONFIG_CRASH_DUMP)	+= crash_dump_$(BITS).o
 obj-y				+= kprobes/
 obj-$(CONFIG_MODULES)		+= module.o
@@ -118,5 +119,4 @@ ifeq ($(CONFIG_X86_64),y)
 
 	obj-$(CONFIG_PCI_MMCONFIG)	+= mmconf-fam10h_64.o
 	obj-y				+= vsmp_64.o
-	obj-$(CONFIG_KEXEC)		+= kexec-bzimage64.o
 endif
diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
index 0553a34fa0df..a618fcd2c07d 100644
--- a/arch/x86/kernel/crash.c
+++ b/arch/x86/kernel/crash.c
@@ -182,8 +182,7 @@ void native_machine_crash_shutdown(struct pt_regs *regs)
 	crash_save_cpu(regs, safe_smp_processor_id());
 }
 
-#ifdef CONFIG_X86_64
-
+#ifdef CONFIG_KEXEC_FILE
 static int get_nr_ram_ranges_callback(unsigned long start_pfn,
 				unsigned long nr_pfn, void *arg)
 {
@@ -696,5 +695,4 @@ int crash_load_segments(struct kimage *image)
 
 	return ret;
 }
-
-#endif /* CONFIG_X86_64 */
+#endif /* CONFIG_KEXEC_FILE */
diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
index 8b04018e5d1f..485981059a40 100644
--- a/arch/x86/kernel/machine_kexec_64.c
+++ b/arch/x86/kernel/machine_kexec_64.c
@@ -25,9 +25,11 @@
 #include <asm/debugreg.h>
 #include <asm/kexec-bzimage64.h>
 
+#ifdef CONFIG_KEXEC_FILE
 static struct kexec_file_ops *kexec_file_loaders[] = {
 		&kexec_bzImage64_ops,
 };
+#endif
 
 static void free_transition_pgtable(struct kimage *image)
 {
@@ -178,6 +180,7 @@ static void load_segments(void)
 		);
 }
 
+#ifdef CONFIG_KEXEC_FILE
 /* Update purgatory as needed after various image segments have been prepared */
 static int arch_update_purgatory(struct kimage *image)
 {
@@ -209,6 +212,12 @@ static int arch_update_purgatory(struct kimage *image)
 
 	return ret;
 }
+#else /* !CONFIG_KEXEC_FILE */
+static inline int arch_update_purgatory(struct kimage *image)
+{
+	return 0;
+}
+#endif /* CONFIG_KEXEC_FILE */
 
 int machine_kexec_prepare(struct kimage *image)
 {
@@ -329,6 +338,7 @@ void arch_crash_save_vmcoreinfo(void)
 
 /* arch-dependent functionality related to kexec file-based syscall */
 
+#ifdef CONFIG_KEXEC_FILE
 int arch_kexec_kernel_image_probe(struct kimage *image, void *buf,
 				  unsigned long buf_len)
 {
@@ -522,3 +532,4 @@ overflow:
 	       (int)ELF64_R_TYPE(rel[i].r_info), value);
 	return -ENOEXEC;
 }
+#endif /* CONFIG_KEXEC_FILE */