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

[Baoquan He]

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
> >}
> >
> 
>