[PATCH] arm64: Force NO_BLOCK_MAPPINGS if crashkernel reservation is required

[Catalin Marinas]

mem_init() currently relies on knowing the boundaries of the crashkernel
reservation to map such region with page granularity for later
unmapping via set_memory_valid(..., 0). If the crashkernel reservation
is deferred, such boundaries are not known when the linear mapping is
created. Simply parse the command line for "crashkernel" and, if found,
create the linear map with NO_BLOCK_MAPPINGS.

Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
Cc: James Morse <james.morse at arm.com>
Cc: Nicolas Saenz Julienne <nsaenzjulienne at suse.de>
---

Following the online (and offline) discussion with James and Nicolas,
this aims to avoid issues with moving the reserve_crashkernel() call to
after the memory map has been created (the ZONE_DMA patches).

https://lore.kernel.org/r/e60d643e-4879-3fc3-737d-2c145332a6d7@arm.com

 arch/arm64/mm/mmu.c | 37 ++++++++++++++++---------------------
 1 file changed, 16 insertions(+), 21 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index d7fe72ee678a..dd214157a026 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -469,6 +469,21 @@ void __init mark_linear_text_alias_ro(void)
 			    PAGE_KERNEL_RO);
 }
 
+static bool crash_mem_map __initdata;
+
+static int __init enable_crash_mem_map(char *arg)
+{
+	/*
+	 * Proper parameter parsing is done by reserve_crashkernel(). We only
+	 * need to know if the linear map has to avoid block mappings so that
+	 * the crashkernel reservations can be unmapped later.
+	 */
+	crash_mem_map = true;
+
+	return 0;
+}
+early_param("crashkernel", enable_crash_mem_map);
+
 static void __init map_mem(pgd_t *pgdp)
 {
 	phys_addr_t kernel_start = __pa_symbol(_stext);
@@ -477,7 +492,7 @@ static void __init map_mem(pgd_t *pgdp)
 	int flags = 0;
 	u64 i;
 
-	if (rodata_full || debug_pagealloc_enabled())
+	if (rodata_full || crash_mem_map || debug_pagealloc_enabled())
 		flags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
 
 	/*
@@ -487,11 +502,6 @@ static void __init map_mem(pgd_t *pgdp)
 	 * the following for-loop
 	 */
 	memblock_mark_nomap(kernel_start, kernel_end - kernel_start);
-#ifdef CONFIG_KEXEC_CORE
-	if (crashk_res.end)
-		memblock_mark_nomap(crashk_res.start,
-				    resource_size(&crashk_res));
-#endif
 
 	/* map all the memory banks */
 	for_each_mem_range(i, &start, &end) {
@@ -518,21 +528,6 @@ static void __init map_mem(pgd_t *pgdp)
 	__map_memblock(pgdp, kernel_start, kernel_end,
 		       PAGE_KERNEL, NO_CONT_MAPPINGS);
 	memblock_clear_nomap(kernel_start, kernel_end - kernel_start);
-
-#ifdef CONFIG_KEXEC_CORE
-	/*
-	 * Use page-level mappings here so that we can shrink the region
-	 * in page granularity and put back unused memory to buddy system
-	 * through /sys/kernel/kexec_crash_size interface.
-	 */
-	if (crashk_res.end) {
-		__map_memblock(pgdp, crashk_res.start, crashk_res.end + 1,
-			       PAGE_KERNEL,
-			       NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS);
-		memblock_clear_nomap(crashk_res.start,
-				     resource_size(&crashk_res));
-	}
-#endif
 }
 
 void mark_rodata_ro(void)