Re: [PATCH v2 15/20] kexec: fill note buffers by NT_VMCORE_PAD notes in page-size boundary

[Zhang Yanfei <zhangyanfei@cn.fujitsu.com>]

于 2013年03月02日 16:37, HATAYAMA Daisuke 写道:
> Fill both crash_notes and vmcoreinfo_note buffers by NT_VMCORE_PAD
> note type to make them satisfy mmap()'s page-size boundary
> requirement.
> 
> So far, end of note segments has been marked by zero-filled elf
> header. Instead, this patch writes NT_VMCORE_PAD note in the end of
> note segments until the offset on page-size boundary.


In the codes below, it seems that you assign name "VMCOREINFO" for
note type NT_VMCORE_PAD, right? This is kind of wired, i think. This
name has been used for NT_VMCORE_DEBUGINFO note already. Why not something
like "VMCOREPAD" or "PAD"?

> 
> Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
> ---
> 
>  arch/s390/include/asm/kexec.h |    7 ++++--
>  include/linux/kexec.h         |   12 ++++++-----
>  kernel/kexec.c                |   46 ++++++++++++++++++++++++++---------------
>  3 files changed, 40 insertions(+), 25 deletions(-)
> 
> diff --git a/arch/s390/include/asm/kexec.h b/arch/s390/include/asm/kexec.h
> index 694bcd6..2a531ce 100644
> --- a/arch/s390/include/asm/kexec.h
> +++ b/arch/s390/include/asm/kexec.h
> @@ -41,8 +41,8 @@
>  /*
>   * 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
> + * Seven notes plus note with NT_VMCORE_PAD type 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 + \
> @@ -53,7 +53,8 @@
>  	 ALIGN(sizeof(u64), 4) + \
>  	 ALIGN(sizeof(u32), 4) + \
>  	 ALIGN(sizeof(u64) * 16, 4) + \
> -	 ALIGN(sizeof(u32), 4) \
> +	 ALIGN(sizeof(u32), 4) + \
> +	 VMCOREINFO_NOTE_NAME_BYTES \
>  	)
>  
>  /* Provide a dummy definition to avoid build failures. */
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index 5113570..6592935 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -47,14 +47,16 @@
>  #define KEXEC_CORE_NOTE_NAME_BYTES ALIGN(sizeof(KEXEC_CORE_NOTE_NAME), 4)
>  #define KEXEC_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.
> + * The per-cpu notes area is a list of notes terminated by a note
> + * header with NT_VMCORE_PAD type. 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 ( (KEXEC_NOTE_HEAD_BYTES * 2) +		\
>  			    KEXEC_CORE_NOTE_NAME_BYTES +		\
> -			    KEXEC_CORE_NOTE_DESC_BYTES )
> +			    KEXEC_CORE_NOTE_DESC_BYTES +		\
> +			    VMCOREINFO_NOTE_NAME_BYTES)
>  #endif
>  
>  /*
> @@ -187,7 +189,7 @@ extern struct kimage *kexec_crash_image;
>  #define VMCOREINFO_NOTE_NAME_BYTES ALIGN(sizeof(VMCOREINFO_NOTE_NAME), 4)
>  #define VMCOREINFO_NOTE_SIZE       ALIGN(KEXEC_NOTE_HEAD_BYTES*2	\
>  					 +VMCOREINFO_BYTES		\
> -					 +VMCOREINFO_NOTE_NAME_BYTES,	\
> +					 +VMCOREINFO_NOTE_NAME_BYTES*2,	\
>  					 PAGE_SIZE)
>  
>  /* Location of a reserved region to hold the crash kernel.
> diff --git a/kernel/kexec.c b/kernel/kexec.c
> index 6597b82..fbdc0f0 100644
> --- a/kernel/kexec.c
> +++ b/kernel/kexec.c
> @@ -40,6 +40,7 @@
>  
>  /* Per cpu memory for storing cpu states in case of system crash. */
>  note_buf_t __percpu *crash_notes;
> +static size_t crash_notes_size = ALIGN(sizeof(note_buf_t), PAGE_SIZE);
>  
>  /* vmcoreinfo stuff */
>  static unsigned char vmcoreinfo_data[VMCOREINFO_BYTES];
> @@ -1177,6 +1178,7 @@ unlock:
>  	return ret;
>  }
>  
> +/* If @data is NULL, fill @buf with 0 in @data_len bytes. */
>  static u32 *append_elf_note(u32 *buf, char *name, unsigned type, void *data,
>  			    size_t data_len)
>  {
> @@ -1189,26 +1191,36 @@ static u32 *append_elf_note(u32 *buf, char *name, unsigned type, void *data,
>  	buf += (sizeof(note) + 3)/4;
>  	memcpy(buf, name, note.n_namesz);
>  	buf += (note.n_namesz + 3)/4;
> -	memcpy(buf, data, note.n_descsz);
> +	if (data)
> +		memcpy(buf, data, note.n_descsz);
> +	else
> +		memset(buf, 0, note.n_descsz);
>  	buf += (note.n_descsz + 3)/4;
>  
>  	return buf;
>  }
>  
> -static void final_note(u32 *buf)
> +static void final_note(u32 *buf, size_t buf_len, size_t data_len)
>  {
> -	struct elf_note note;
> +	size_t used_bytes, pad_hdr_size;
>  
> -	note.n_namesz = 0;
> -	note.n_descsz = 0;
> -	note.n_type   = 0;
> -	memcpy(buf, &note, sizeof(note));
> +	pad_hdr_size = KEXEC_NOTE_HEAD_BYTES + VMCOREINFO_NOTE_NAME_BYTES;
> +
> +	/*
> +	 * keep space for ELF note header and "VMCOREINFO" name to
> +	 * terminate ELF segment by NT_VMCORE_PAD note.
> +	 */
> +	BUG_ON(data_len + pad_hdr_size > buf_len);
> +
> +	used_bytes = data_len + pad_hdr_size;
> +	append_elf_note(buf, VMCOREINFO_NOTE_NAME, NT_VMCORE_PAD, NULL,
> +			roundup(used_bytes, PAGE_SIZE) - used_bytes);
>  }
>  
>  void crash_save_cpu(struct pt_regs *regs, int cpu)
>  {
>  	struct elf_prstatus prstatus;
> -	u32 *buf;
> +	u32 *buf, *buf_end;
>  
>  	if ((cpu < 0) || (cpu >= nr_cpu_ids))
>  		return;
> @@ -1226,16 +1238,15 @@ void crash_save_cpu(struct pt_regs *regs, int cpu)
>  	memset(&prstatus, 0, sizeof(prstatus));
>  	prstatus.pr_pid = current->pid;
>  	elf_core_copy_kernel_regs(&prstatus.pr_reg, regs);
> -	buf = append_elf_note(buf, KEXEC_CORE_NOTE_NAME, NT_PRSTATUS,
> -		      	      &prstatus, sizeof(prstatus));
> -	final_note(buf);
> +	buf_end = append_elf_note(buf, KEXEC_CORE_NOTE_NAME, NT_PRSTATUS,
> +				  &prstatus, sizeof(prstatus));
> +	final_note(buf_end, crash_notes_size, (buf_end - buf) * sizeof(u32));
>  }
>  
>  static int __init crash_notes_memory_init(void)
>  {
>  	/* Allocate memory for saving cpu registers. */
> -	crash_notes = __alloc_percpu(roundup(sizeof(note_buf_t), PAGE_SIZE),
> -				     PAGE_SIZE);
> +	crash_notes = __alloc_percpu(crash_notes_size, PAGE_SIZE);
>  	if (!crash_notes) {
>  		printk("Kexec: Memory allocation for saving cpu register"
>  		" states failed\n");
> @@ -1434,13 +1445,14 @@ int __init parse_crashkernel_low(char *cmdline,
>  
>  static void update_vmcoreinfo_note(void)
>  {
> -	u32 *buf = vmcoreinfo_note;
> +	u32 *buf = vmcoreinfo_note, *buf_end;
>  
>  	if (!vmcoreinfo_size)
>  		return;
> -	buf = append_elf_note(buf, VMCOREINFO_NOTE_NAME, NT_VMCORE_DEBUGINFO,
> -			      vmcoreinfo_data, vmcoreinfo_size);
> -	final_note(buf);
> +	buf_end = append_elf_note(buf, VMCOREINFO_NOTE_NAME, NT_VMCORE_DEBUGINFO,
> +				  vmcoreinfo_data, vmcoreinfo_size);
> +	final_note(buf_end, sizeof(vmcoreinfo_note),
> +		   (buf_end - buf) * sizeof(u32));
>  }
>  
>  void crash_save_vmcoreinfo(void)
> 
> 
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