linux-kernel - Re: [PATCH 4/5] arm: Add kexec_image

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Date:   Mon, 01 Jun 2020 18:30:22 +0200
From:   Lukasz Stelmach <l.stelmach@...sung.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     Masahiro Yamada <masahiroy@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Enrico Weigelt <info@...ux.net>,
        Kees Cook <keescook@...omium.org>,
        Ingo Molnar <mingo@...nel.org>,
        Ben Dooks <ben-linux@...ff.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH 4/5] arm: Add kexec_image_info

It was <2020-06-01 pon 15:56>, when Russell King - ARM Linux admin wrote:
> On Mon, Jun 01, 2020 at 04:27:53PM +0200, Łukasz Stelmach wrote:
>> Add kexec_image_info to print detailed information about a kexec image.
>
> Isn't this already visible through kexec debugging?  Why do we need
> to duplicate the same output in the kernel?  Do we think that the
> kexec interfaces are that fragile that they don't work?

Because:

    + kexec_image_info is required if we want to show information for an
      image loaded via kexec_file_load (with kexec-tools or any other
      tool e.g. u-root),
    + this is where both interfaces meet and it is easy to compare
      their results,
    + I consider showing results as close to the end of a code path as
      possible more reliable.

>> 
>> Signed-off-by: Łukasz Stelmach <l.stelmach@...sung.com>
>> ---
>>  arch/arm/kernel/machine_kexec.c | 28 ++++++++++++++++++++++++++++
>>  1 file changed, 28 insertions(+)
>> 
>> diff --git a/arch/arm/kernel/machine_kexec.c b/arch/arm/kernel/machine_kexec.c
>> index 76300f3813e8..c10a2dfd53d1 100644
>> --- a/arch/arm/kernel/machine_kexec.c
>> +++ b/arch/arm/kernel/machine_kexec.c
>> @@ -31,6 +31,32 @@ extern unsigned long kexec_boot_atags;
>>  
>>  static atomic_t waiting_for_crash_ipi;
>>  
>> +/**
>> + * kexec_image_info - For debugging output.
>> + */
>> +#define kexec_image_info(_i) _kexec_image_info(__func__, __LINE__, _i)
>> +static void _kexec_image_info(const char *func, int line,
>> +	const struct kimage *kimage)
>> +{
>> +	unsigned long i;
>> +
>> +	pr_debug("%s:%d:\n", func, line);
>> +	pr_debug("  kexec kimage info:\n");
>> +	pr_debug("    type:        %d\n", kimage->type);
>> +	pr_debug("    start:       %lx\n", kimage->start);
>> +	pr_debug("    head:        %lx\n", kimage->head);
>> +	pr_debug("    nr_segments: %lu\n", kimage->nr_segments);
>> +
>> +	for (i = 0; i < kimage->nr_segments; i++) {
>> +		pr_debug("      segment[%lu]: %08lx - %08lx, 0x%x bytes, %lu pages\n",
>> +			i,
>> +			kimage->segment[i].mem,
>> +			kimage->segment[i].mem + kimage->segment[i].memsz,
>> +			kimage->segment[i].memsz,
>> +			kimage->segment[i].memsz /  PAGE_SIZE);
>> +	}
>> +}
>> +
>>  /*
>>   * Provide a dummy crash_notes definition while crash dump arrives to arm.
>>   * This prevents breakage of crash_notes attribute in kernel/ksysfs.c.
>> @@ -42,6 +68,8 @@ int machine_kexec_prepare(struct kimage *image)
>>  	__be32 header;
>>  	int i, err;
>>  
>> +	kexec_image_info(image);
>> +
>>  	image->arch.kernel_r2 = image->start - KEXEC_ARM_ZIMAGE_OFFSET
>>  				     + KEXEC_ARM_ATAGS_OFFSET;
>>  
>> -- 
>> 2.26.2
>> 
>> 

-- 
Łukasz Stelmach
Samsung R&D Institute Poland
Samsung Electronics

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