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SubjectRe: [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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