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Date: Mon, 27 Aug 2018 15:01:09 +0800 From: Baoquan He <bhe@...hat.com> To: Chao Fan <fanc.fnst@...fujitsu.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 08/27/18 at 02:28pm, 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: > 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. Yes, we are saying the same thing. if num_immovable_mem == 0, it covers all the cases you listed at below. Here I assume you have taken num_immovable_mem definition out. #ifdef CONFIG_MEMORY_HOTREMOVE /* Store the immovable memory regions */ static struct mem_vector immovable_mem[MAX_NUMNODES*2]; #endif /* Store the amount of immovable memory regions */ static int num_immovable_mem; > > 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 > >} > > > >
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