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

On Thu, Dec 03, 2020 at 03:36:10PM -0800, Andrew Morton wrote:

On Thu,  3 Dec 2020 08:29:43 +0200 Mike Rapoport [off-list ref] wrote:

quoted

From: Mike Rapoport <redacted>

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)

Thanks for updating!

-- 
Sincerely yours,
Mike.

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