[PATCH v6 1/2] powerpc/fadump: reduce memory consumption for capture kernel

[Michal Suchánek]

Hello,

sorry about the late reply.

Looks like I had too much faith in the parse_args sanity.

Looking closely the parsing happens in next_arg and only outermost
quotes are removed.

So presumably >>foo="bar baz"<< gives >>bar baz<< as value and
 >>foo=bar" baz"<< gives >>bar" baz<< as value.

And presumably you can do fadump_extra_args="par1=val1 par2=val2
pa3=val3" and fadump_extra_args=""par="value with
spaces""" (each parameter which needs space in separate
fadump_extra_args parameter) provided you remove the outermost quotes
in the fadump_extra_args handler as well.

Wanted to run some tests but did not get around to do it yet.

On Sat, 29 Jul 2017 02:27:22 +0530
Hari Bathini <hbathini at linux.vnet.ibm.com> wrote:

> With fadump (dump capture) kernel booting like a regular kernel, it
> almost needs the same amount of memory to boot as the production
> kernel, which is unwarranted for a dump capture kernel. But with no
> option to disable some of the unnecessary subsystems in fadump
> kernel, that much memory is wasted on fadump, depriving the
> production kernel of that memory.
> 
> Introduce kernel parameter 'fadump_extra_args=' that would take
> regular parameters as a space separated quoted string, to be enforced
> when fadump is active. This 'fadump_extra_args=' parameter can be
> leveraged to pass parameters like nr_cpus=1, cgroup_disable=memory
> and numa=off, to disable unwarranted resources/subsystems.
> 
> Also, ensure the log "Firmware-assisted dump is active" is printed
> early in the boot process to put the subsequent fadump messages in
> context.
> 
> Suggested-by: Michael Ellerman <mpe at ellerman.id.au>
> Signed-off-by: Hari Bathini <hbathini at linux.vnet.ibm.com>
> ---
> 
> Changes from v5:
> * Using 'fadump_extra_args=' instead of 'fadump_append=' to pass
>   additional parameters, to be enforced when fadump is active.
> * Using space-separated quoted list as syntax for 'fadump_extra_args='
>   parameter.
> 
> 
>  arch/powerpc/include/asm/fadump.h |    2 +
>  arch/powerpc/kernel/fadump.c      |  125
> ++++++++++++++++++++++++++++++++++++-
> arch/powerpc/kernel/prom.c        |    7 ++ 3 files changed, 131
> insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/fadump.h
> b/arch/powerpc/include/asm/fadump.h index ce88bbe..98ae009 100644
> --- a/arch/powerpc/include/asm/fadump.h
> +++ b/arch/powerpc/include/asm/fadump.h
> @@ -208,11 +208,13 @@ extern int early_init_dt_scan_fw_dump(unsigned
> long node, const char *uname, int depth, void *data);
>  extern int fadump_reserve_mem(void);
>  extern int setup_fadump(void);
> +extern void enforce_fadump_extra_args(char *cmdline);
>  extern int is_fadump_active(void);
>  extern void crash_fadump(struct pt_regs *, const char *);
>  extern void fadump_cleanup(void);
>  
>  #else	/* CONFIG_FA_DUMP */
> +static inline void enforce_fadump_extra_args(char *cmdline) { }
>  static inline int is_fadump_active(void) { return 0; }
>  static inline void crash_fadump(struct pt_regs *regs, const char
> *str) { } #endif
> diff --git a/arch/powerpc/kernel/fadump.c
> b/arch/powerpc/kernel/fadump.c index dc0c49c..d8cb829 100644
> --- a/arch/powerpc/kernel/fadump.c
> +++ b/arch/powerpc/kernel/fadump.c
> @@ -78,8 +78,10 @@ int __init early_init_dt_scan_fw_dump(unsigned
> long node,
>  	 * dump data waiting for us.
>  	 */
>  	fdm_active = of_get_flat_dt_prop(node, "ibm,kernel-dump",
> NULL);
> -	if (fdm_active)
> +	if (fdm_active) {
> +		pr_info("Firmware-assisted dump is active.\n");
>  		fw_dump.dump_active = 1;
> +	}
>  
>  	/* Get the sizes required to store dump data for the
> firmware provided
>  	 * dump sections.
> @@ -332,8 +334,11 @@ int __init fadump_reserve_mem(void)
>  {
>  	unsigned long base, size, memory_boundary;
>  
> -	if (!fw_dump.fadump_enabled)
> +	if (!fw_dump.fadump_enabled) {
> +		if (fw_dump.dump_active)
> +			pr_warn("Firmware-assisted dump was active
> but kernel booted with fadump disabled!\n"); return 0;
> +	}
>  
>  	if (!fw_dump.fadump_supported) {
>  		printk(KERN_INFO "Firmware-assisted dump is not
> supported on" @@ -373,7 +378,6 @@ int __init fadump_reserve_mem(void)
>  		memory_boundary = memblock_end_of_DRAM();
>  
>  	if (fw_dump.dump_active) {
> -		printk(KERN_INFO "Firmware-assisted dump is
> active.\n"); /*
>  		 * If last boot has crashed then reserve all the
> memory
>  		 * above boot_memory_size so that we don't touch it
> until @@ -460,6 +464,121 @@ static int __init
> early_fadump_reserve_mem(char *p) }
>  early_param("fadump_reserve_mem", early_fadump_reserve_mem);
>  
> +#define FADUMP_EXTRA_ARGS_PARAM		"fadump_extra_args="
> +#define INIT_ARGS_START			"-- "
> +#define INIT_ARGS_START_LEN		strlen(INIT_ARGS_START)
> +
> +struct param_info {
> +	char		*params;
> +	unsigned int	len;
> +	unsigned int	index;
> +};
> +
> +static void __init fadump_update_params(struct param_info
> *param_info,
> +					char *val, unsigned int len,
> +					bool split_params)
> +{
> +	bool add_quotes = (split_params ? false :
> +			   ((strchr(val, ' ') != NULL) ? true :
> false)); +
> +	if (add_quotes)
> +		param_info->params[param_info->index++] = '"';

This is not safe. You do not know if any quotes were removed so you
should not blindly add them. Instead you should copy the value at the
place where the argument was found (which you currently do not get but
could be added in the argument struct or as extra argument to the
callback).

> +
> +	strncpy(param_info->params + param_info->index, val, len);
> +	param_info->index += len;
> +
> +	if (add_quotes)
> +		param_info->params[param_info->index++] = '"';
> +}
> +
> +/*
> + * Reworks command line parameters and splits 'fadump_extra_args='
> param
> + * to enforce the parameters passed through it
> + */
> +static int __init fadump_rework_cmdline_params(char *param, char
> *val,
> +					       const char *unused,
> void *arg) +{
> +	unsigned int len;
> +	struct param_info *param_info = (struct param_info *)arg;
> +	bool split_params = false;
> +
> +	if (!strncmp(param, FADUMP_EXTRA_ARGS_PARAM,
> +		     (strlen(FADUMP_EXTRA_ARGS_PARAM) - 1)))
> +		split_params = true;
> +
> +	len = strlen(param);
> +	fadump_update_params(param_info, param, len, split_params);
> +
> +	len = (val != NULL) ? strlen(val) : 0;
> +	if (len) {
> +		param_info->params[param_info->index++] =
> +						split_params ? ' ' :
> '=';
> +		fadump_update_params(param_info, val, len,
> split_params);
> +	}
> +
> +	param_info->params[param_info->index++] = ' ';
> +
> +	return 0;
> +}
> +
> +/*
> + * Replace every occurrence of 'fadump_extra_args="param1 param2
> param3"'
> + * in cmdline with 'fadump_extra_args param1 param2 param3' by
> stripping
> + * off '=' and quotes, if any. This ensures that the additional
> parameters
> + * passed with 'fadump_extra_args=' are enforced.
> + */
> +void __init enforce_fadump_extra_args(char *cmdline)
> +{
> +	static char tmp_cmdline[COMMAND_LINE_SIZE] __initdata;
> +	static char init_cmdline[COMMAND_LINE_SIZE] __initdata;
> +	struct param_info param_info;
> +	char *args;
> +
> +	if (strstr(cmdline, FADUMP_EXTRA_ARGS_PARAM) == NULL)
> +		return;
> +
> +	pr_info("Modifying command line to enforce the additional
> parameters passed through 'fadump_extra_args='"); +
> +	param_info.params = cmdline;
> +	param_info.len = strlen(cmdline);
> +	param_info.index = 0;
> +
> +	strlcpy(init_cmdline, cmdline, COMMAND_LINE_SIZE);
> +
> +	strlcpy(tmp_cmdline, cmdline, COMMAND_LINE_SIZE);
> +	while (1) {
> +		parse_args("fadump params", tmp_cmdline, NULL, 0, 0,
> 0,
> +			   &param_info,
> &fadump_rework_cmdline_params); +

You should probably use the argument structure and amend it to include
whatever extra information is needed rather than the unknown parameter
hook.

> +		/*
> +		 * parse_args() stops at '--'. Keep going if there
> are more
> +		 * parameters as we are supposed to look at all
> parameters
> +		 * in this case. Otherwise, break.

You should not do this. If people pass fadump_extra_args to init it's
their choice.

On the other hand, when fadump_extra_args contains a -- any subsequent
parameters are turned into init arguments which is probably not wanted.

Thanks

Michal