[PATCH v14 04/10] set_memory: allow querying whether set_direct_map_*() is actually enabled

[Andrew Morton]

On Thu,  3 Dec 2020 08:29:43 +0200 Mike Rapoport <rppt at kernel.org> wrote:

> From: Mike Rapoport <rppt at linux.ibm.com>
> 
> On arm64, set_direct_map_*() functions may return 0 without actually
> changing the linear map. This behaviour can be controlled using kernel
> parameters, so we need a way to determine at runtime whether calls to
> set_direct_map_invalid_noflush() and set_direct_map_default_noflush() have
> any effect.
> 
> Extend set_memory API with can_set_direct_map() function that allows
> checking if calling set_direct_map_*() will actually change the page table,
> replace several occurrences of open coded checks in arm64 with the new
> function and provide a generic stub for architectures that always modify
> page tables upon calls to set_direct_map APIs.
> 
> ...
>
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -22,6 +22,7 @@
>  #include <linux/io.h>
>  #include <linux/mm.h>
>  #include <linux/vmalloc.h>
> +#include <linux/set_memory.h>
>  
>  #include <asm/barrier.h>
>  #include <asm/cputype.h>
> @@ -477,7 +478,7 @@ static void __init map_mem(pgd_t *pgdp)
>  	int flags = 0;
>  	u64 i;
>  
> -	if (rodata_full || debug_pagealloc_enabled())
> +	if (can_set_direct_map())
>  		flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;

Changes in -next turned this into

	if (can_set_direct_map() || crash_mem_map)