linux-kernel - Re: [PATCH v5 4/4] x86/boot/KASLR: Limit kaslr to choosing the immovable memory

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Message-ID: <20180827063135.GE6769@localhost.localdomain>
Date:   Mon, 27 Aug 2018 14:31:35 +0800
From:   Chao Fan <fanc.fnst@...fujitsu.com>
To:     Baoquan He <bhe@...hat.com>
CC:     <tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>,
        <x86@...nel.org>, <linux-kernel@...r.kernel.org>,
        <keescook@...omium.org>, <n-horiguchi@...jp.nec.com>,
        <indou.takao@...fujitsu.com>, <caoj.fnst@...fujitsu.com>,
        <douly.fnst@...fujitsu.com>
Subject: Re: [PATCH v5 4/4] x86/boot/KASLR: Limit kaslr to choosing the
 immovable memory

On Mon, Aug 27, 2018 at 02:28:54PM +0800, Chao Fan wrote:
>On Mon, Aug 27, 2018 at 01:56:07PM +0800, Baoquan He wrote:
>>On 08/07/18 at 02:50pm, Chao Fan wrote:
[...]
>>
>>Is it possible to take num_immovable_mem definition out from #ifdef
>>CONFIG_MEMORY_HOTREMOVE block and check it here like below? This way,
>>one level of indentation can be reduced in the for loop, and code is
>>more readable.
>>
>
>I think there is a mistake.
>
>The logical is:
>if (#ifdef CONFIG_MEMORY_HOTREMOVE) && (num_immovable_mem > 0)
>	then A;
>else
>	then B;
>
>But below is:

Sorry for that, here the 'below' means the code in your mail.

Thanks,
Chao Fan

>if (num_immovable_mem > 0)
>	then B;
>else if (#ifdef CONFIG_MEMORY_HOTREMOVE)
>	then A;
>else
>	nothing;
>
>The precondition of the loop is (num_immovable_mem > 0), because
>there is only one condition that we need go the A code:
>CONFIG_MEMORY_HOTREMOVE is defined, and memory information in srat
>found.
>
>But there is many conditions we go the B code:
>1. CONFIG_MEMORY_HOTREMOVE is not defined.
>2. CONFIG_MEMORY_HOTREMOVE defined, but we didn't get the right acpi tables
>3. CONFIG_MEMORY_HOTREMOVE defined, or there is only one node in this machine.
>
>Yes, the code is hard to read, but you have changed the logical, there
>is a compromise method, I don't know whether is better:
>
>#ifdef CONFIG_MEMORY_HOTREMOVE
>	if (num_immovable_mem == 0)
>		goto B;
>
>	for (i = 0; i < num_immovable_mem; i++) {
>		...
>	}
>#endif
>
>B:
>	slots_count(region, minimum, image_size);
>	
>	if (slot_area_index == MAX_SLOT_AREA) {
>		debug_putstr("Aborted e820/efi memmap scan (slot_areas full)!\n");
>		return 1;
>	}
>	return 0;
>	
>
>>
>>static bool process_mem_region(struct mem_vector *region,
>>			       unsigned long long minimum,
>>			       unsigned long long image_size)
>>{
>>
>>	/*
>>	 * If no immovable memory found, or MEMORY_HOTREMOVE disabled,
>>	 * walk all the regions, so use region directely.
>>	 */
>>	if (num_immovable_mem > 0) {
>>		slots_count(region, minimum, image_size);
>>		
>>		if (slot_area_index == MAX_SLOT_AREA) {
>>			debug_putstr("Aborted e820/efi memmap scan (slot_areas full)!\n");
>>			return 1;
>>		}
>>		return 0;
>>	}
>>
>>#ifdef CONFIG_MEMORY_HOTREMOVE
>>	for (i = 0; i < num_immovable_mem; i++) {
>>		...
>>	}
>>#endif
>>}
>>