[patch 007/114] kexec: export the value of phys_base instead of symbol address

[patch 007/114] kexec: export the value of phys_base instead of symbol address

[akpm]

From: Baoquan He <bhe@redhat.com>
Subject: kexec: export the value of phys_base instead of symbol address

Currently in x86_64, the symbol address of phys_base is exported to
vmcoreinfo.  Dave Anderson complained this is really useless for his Crash
implementation.  Because in user-space utility Crash and Makedumpfile
which exported vmcore information is mainly used for, value of phys_base
is needed to covert virtual address of exported kernel symbol to physical
address.  Especially init_level4_pgt, if we want to access and go over the
page table to look up a PA corresponding to VA, firstly we need calculate

  page_dir = SYMBOL(init_level4_pgt) - __START_KERNEL_map + phys_base;

Now in Crash and Makedumpfile, we have to analyze the vmcore elf program
header to get value of phys_base.  As Dave said, it would be preferable if
it were readily availabl in vmcoreinfo rather than depending upon the
PT_LOAD semantics.

Hence in this patch change to export the value of phys_base instead of its
virtual address.

And people also complained that KERNEL_IMAGE_SIZE exporting is x86_64
only, should be moved into arch dependent function
arch_crash_save_vmcoreinfo.  Do the moving in this patch.

Link: http://lkml.kernel.org/r/1478568596-30060-2-git-send-email-bhe@redhat.com
Signed-off-by: Baoquan He <bhe@redhat.com>
Cc: Thomas Garnier <thgarnie@google.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Xunlei Pang <xlpang@redhat.com>
Cc: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Eugene Surovegin <surovegin@google.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: AKASHI Takahiro <takahiro.akashi@linaro.org>
Cc: Atsushi Kumagai <ats-kumagai@wm.jp.nec.com>
Cc: Dave Anderson <anderson@redhat.com>
Cc: Pratyush Anand <panand@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/x86/kernel/machine_kexec_64.c |    3 ++-
 kernel/kexec_core.c                |    3 ---
 2 files changed, 2 insertions(+), 4 deletions(-)

diff -puN arch/x86/kernel/machine_kexec_64.c~kexec-change-to-export-the-value-of-phys_base-instead-of-symbol-address arch/x86/kernel/machine_kexec_64.c
--- a/arch/x86/kernel/machine_kexec_64.c~kexec-change-to-export-the-value-of-phys_base-instead-of-symbol-address
+++ a/arch/x86/kernel/machine_kexec_64.c
@@ -328,7 +328,7 @@ void machine_kexec(struct kimage *image)
 
 void arch_crash_save_vmcoreinfo(void)
 {
-	VMCOREINFO_SYMBOL(phys_base);
+	VMCOREINFO_NUMBER(phys_base);
 	VMCOREINFO_SYMBOL(init_level4_pgt);
 
 #ifdef CONFIG_NUMA
@@ -337,6 +337,7 @@ void arch_crash_save_vmcoreinfo(void)
 #endif
 	vmcoreinfo_append_str("KERNELOFFSET=%lx\n",
 			      kaslr_offset());
+	VMCOREINFO_NUMBER(KERNEL_IMAGE_SIZE);
 }
 
 /* arch-dependent functionality related to kexec file-based syscall */
diff -puN kernel/kexec_core.c~kexec-change-to-export-the-value-of-phys_base-instead-of-symbol-address kernel/kexec_core.c
--- a/kernel/kexec_core.c~kexec-change-to-export-the-value-of-phys_base-instead-of-symbol-address
+++ a/kernel/kexec_core.c
@@ -1467,9 +1467,6 @@ static int __init crash_save_vmcoreinfo_
 #endif
 	VMCOREINFO_NUMBER(PG_head_mask);
 	VMCOREINFO_NUMBER(PAGE_BUDDY_MAPCOUNT_VALUE);
-#ifdef CONFIG_X86
-	VMCOREINFO_NUMBER(KERNEL_IMAGE_SIZE);
-#endif
 #ifdef CONFIG_HUGETLB_PAGE
 	VMCOREINFO_NUMBER(HUGETLB_PAGE_DTOR);
 #endif
_