Re: [PATCH] s390/crash: Fix KEXEC_NOTE_BYTES definition

Michael Holzheu
2017-06-21T17:44:23Z

Am Fri, 9 Jun 2017 10:17:05 +0800
schrieb Xunlei Pang <xlpang@redhat.com>:

> S390 KEXEC_NOTE_BYTES is not used by note_buf_t as before, which
> is now defined as follows:
> typedef u32 note_buf_t[CRASH_CORE_NOTE_BYTES/4];
> It was changed by the CONFIG_CRASH_CORE feature.
>
> This patch gets rid of all the old KEXEC_NOTE_BYTES stuff, and
> renames KEXEC_NOTE_BYTES to CRASH_CORE_NOTE_BYTES for S390.
>
> Fixes: 692f66f26a4c ("crash: move crashkernel parsing and vmcore related code under CONFIG_CRASH_CORE")
> Cc: Dave Young <dyoung@redhat.com>
> Cc: Dave Anderson <anderson@redhat.com>
> Cc: Hari Bathini <hbathini@linux.vnet.ibm.com>
> Cc: Gustavo Luiz Duarte <gustavold@linux.vnet.ibm.com>
> Signed-off-by: Xunlei Pang <xlpang@redhat.com>

Hello Xunlei,

As you already know on s390 we create the ELF header in the new kernel.
Therefore we don't use the per-cpu buffers for ELF notes to store
the register state.

For RHEL7 we still store the registers in machine_kexec.c:add_elf_notes().
Though we also use the ELF header from new kernel ...

We assume your original problem with the "kmem -s" failure
was caused by the memory overwrite due to the invalid size of the
"crash_notes" per-cpu buffers.

Therefore your patch looks good for RHEL7 but for upstream we propose the
patch below.
---
[PATCH] s390/crash: Remove unused KEXEC_NOTE_BYTES

After commmit 692f66f26a4c19 ("crash: move crashkernel parsing and vmcore
related code under CONFIG_CRASH_CORE") the KEXEC_NOTE_BYTES macro is not
used anymore and for s390 we create the ELF header in the new kernel
anyway. Therefore remove the macro.

Reported-by: Xunlei Pang <xpang@redhat.com>
Reviewed-by: Mikhail Zaslonko <zaslonko@linux.vnet.ibm.com>
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
---
arch/s390/include/asm/kexec.h | 18 ------------------
include/linux/crash_core.h | 5 +++++
include/linux/kexec.h | 9 ---------
3 files changed, 5 insertions(+), 27 deletions(-)

diff --git a/arch/s390/include/asm/kexec.h b/arch/s390/include/asm/kexec.h
index 2f924bc30e35..dccf24ee26d3 100644
--- a/arch/s390/include/asm/kexec.h
+++ b/arch/s390/include/asm/kexec.h
@@ -41,24 +41,6 @@
/* The native architecture */
#define KEXEC_ARCH KEXEC_ARCH_S390

-/*
- * Size for s390x ELF notes per CPU
- *
- * Seven notes plus zero note at the end: prstatus, fpregset, timer,
- * tod_cmp, tod_reg, control regs, and prefix
- */
-#define KEXEC_NOTE_BYTES \
- (ALIGN(sizeof(struct elf_note), 4) * 8 + \
- ALIGN(sizeof("CORE"), 4) * 7 + \
- ALIGN(sizeof(struct elf_prstatus), 4) + \
- ALIGN(sizeof(elf_fpregset_t), 4) + \
- ALIGN(sizeof(u64), 4) + \
- ALIGN(sizeof(u64), 4) + \
- ALIGN(sizeof(u32), 4) + \
- ALIGN(sizeof(u64) * 16, 4) + \
- ALIGN(sizeof(u32), 4) \
- )
-
/* Provide a dummy definition to avoid build failures. */
static inline void crash_setup_regs(struct pt_regs *newregs,
struct pt_regs *oldregs) { }
diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
index 541a197ba4a2..4090a42578a8 100644
--- a/include/linux/crash_core.h
+++ b/include/linux/crash_core.h
@@ -10,6 +10,11 @@
#define CRASH_CORE_NOTE_NAME_BYTES ALIGN(sizeof(CRASH_CORE_NOTE_NAME), 4)
#define CRASH_CORE_NOTE_DESC_BYTES ALIGN(sizeof(struct elf_prstatus), 4)

+/*
+ * The per-cpu notes area is a list of notes terminated by a "NULL"
+ * note header. For kdump, the code in vmcore.c runs in the context
+ * of the second kernel to combine them into one note.
+ */
#define CRASH_CORE_NOTE_BYTES ((CRASH_CORE_NOTE_HEAD_BYTES * 2) + \
CRASH_CORE_NOTE_NAME_BYTES + \
CRASH_CORE_NOTE_DESC_BYTES)
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index c9481ebcbc0c..65888418fb69 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -63,15 +63,6 @@
#define KEXEC_CORE_NOTE_NAME CRASH_CORE_NOTE_NAME

/*
- * The per-cpu notes area is a list of notes terminated by a "NULL"
- * note header. For kdump, the code in vmcore.c runs in the context
- * of the second kernel to combine them into one note.
- */
-#ifndef KEXEC_NOTE_BYTES
-#define KEXEC_NOTE_BYTES CRASH_CORE_NOTE_BYTES
-#endif
-
-/*
* This structure is used to hold the arguments that are used when loading
* kernel binaries.
*/
--
2.11.2