linux-kernel - Re: [PATCH v9 03/11] arm64: kexec_file: invoke the kernel without purgatory

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Message-ID: <fbd2c6c6-be20-a9fa-0303-e4448225df18@arm.com>
Date:   Tue, 15 May 2018 17:15:52 +0100
From:   James Morse <james.morse@....com>
To:     AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:     catalin.marinas@....com, will.deacon@....com, dhowells@...hat.com,
        vgoyal@...hat.com, herbert@...dor.apana.org.au,
        davem@...emloft.net, dyoung@...hat.com, bhe@...hat.com,
        arnd@...db.de, ard.biesheuvel@...aro.org, bhsharma@...hat.com,
        kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 03/11] arm64: kexec_file: invoke the kernel without
 purgatory

Hi Akashi,

On 15/05/18 05:45, AKASHI Takahiro wrote:
> On Fri, May 11, 2018 at 06:03:49PM +0100, James Morse wrote:
>> On 07/05/18 06:22, AKASHI Takahiro wrote:
>>> On Tue, May 01, 2018 at 06:46:06PM +0100, James Morse wrote:
>>>> On 25/04/18 07:26, AKASHI Takahiro wrote:
>>>>> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
>>>>> index f76ea92dff91..f7dbba00be10 100644
>>>>> --- a/arch/arm64/kernel/machine_kexec.c
>>>>> +++ b/arch/arm64/kernel/machine_kexec.c
>>>>> @@ -205,10 +205,17 @@ void machine_kexec(struct kimage *kimage)
>>
>>>>>  	cpu_soft_restart(kimage != kexec_crash_image,
>>>>> -		reboot_code_buffer_phys, kimage->head, kimage->start, 0);
>>>>> +		reboot_code_buffer_phys, kimage->head, kimage->start,
>>>>> +#ifdef CONFIG_KEXEC_FILE
>>>>> +				kimage->purgatory_info.purgatory_buf ?
>>>>> +						0 : kimage->arch.dtb_mem);
>>>>> +#else
>>>>> +				0);
>>>>> +#endif
>>
>>
>>>> purgatory_buf seems to only be set in kexec_purgatory_setup_kbuf(), called from
>>>> kexec_load_purgatory(), which we don't use. How does this get a value?
>>>>
>>>> Would it be better to always use kimage->arch.dtb_mem, and ensure that is 0 for
>>>> regular kexec (as we can't know where the dtb is)? (image_arg may then be a
>>>> better name).
>>>
>>> The problem is arch.dtb_mem is currently defined only if CONFIG_KEXEC_FILE.
>>
>> I thought it was ARCH_HAS_KIMAGE_ARCH, which we can define all the time if
>> that's what we want.
>>
>>
>>> So I would like to
>>> - merge this patch with patch#8
>>> - change the condition
>>>         #ifdef CONFIG_KEXEC_FILE
>>>        				kimage->file_mode ? kimage->arch.dtb_mem : 0);
>>>         #else
>>>         			0);
>>>         #endif
>>
>> If we can avoid even this #ifdef by always having kimage->arch, I'd prefer that.
>> If we do that 'dtb_mem' would need some thing that indicates its for kexec_file,
>> as kexec has a DTB too, we just don't know where it is...
> 
> OK, but I want to have a minimum of kexec.arch always exist.

I'm curious, why? Its 32bytes that is allocated a maximum of twice.

(my questions on what needs to go in there were because it looked like a third
user was missing...)


> How about this?
>
> | struct kimage_arch {
> | 	phys_addr_t dtb_mem;
> | #ifdef CONFIG_KEXEC_FILE

#ifdef in structs just breeds more #ifdefs, as the code that accesses those
members has to be behind the same set of conditions.

Given this, I prefer the #ifdefs around cpu_soft_restart() as it doesn't force
us to add more #ifdefs later.

For either option without purgatory_info:
Reviewed-by: James Morse <james.morse@....com>


Thanks,

James