Re: [PATCH v14 5/5] x86/boot/KASLR: Limit KASLR to extracting kernel in immovable memory

[Ingo Molnar]

* Chao Fan <fanc.fnst@xxxxxxxxxxxxxx> wrote:

> KASLR randomly chooses some positions which may locate in movable
> memory regions. It will break memory hotplug feature and make the
> movable memory chosen by KASLR practically immovable.
> 
> The solution is to limit KASLR to choose memory regions in immovable
> node according to SRAT tables.
> When CONFIG_EARLY_PARSE_RSDP is enabled, walk through SRAT to get the
> information of immovable memory so that KASLR knows where should be
> chosen for randomization.
> 
> Rename process_mem_region() as __process_mem_region() and name new
> function as process_mem_region().
> 
> Signed-off-by: Chao Fan <fanc.fnst@xxxxxxxxxxxxxx>
> ---
>  arch/x86/boot/compressed/kaslr.c | 75 +++++++++++++++++++++++++++-----
>  1 file changed, 64 insertions(+), 11 deletions(-)

Ok, I like this basic approach of automatically detecing memory areas we 
should not KASLR into - it's far better than earlier iterations.

> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -97,6 +97,11 @@ static bool memmap_too_large;
>  /* Store memory limit specified by "mem=nn[KMG]" or "memmap=nn[KMG]" */
>  static unsigned long long mem_limit = ULLONG_MAX;
>  
> +#ifdef CONFIG_EARLY_SRAT_PARSE
> +/* The immovable memory regions */
> +extern struct mem_vector immovable_mem[MAX_NUMNODES*2];
> +#endif

What logic is the maximum size of this array based on?

Thanks,

	Ingo