arm64: kdump: Try not to use NO_BLOCK_MAPPINGS for memory under 4G

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I545H8
CVE: NA

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For the case crashkernel=X@offset and crashkernel=X,high, we've explicitly
used 'crashk_res' to mark the scope of the page-level mapping required, so
NO_BLOCK_MAPPINGS should not be required for other areas. Otherwise,
system performance will be affected. In fact, only the case crashkernel=X
requires page-level mapping for all low memory under 4G because it
attempts high memory after it fails to request low memory first, and we
cannot predict its final location.
Signed-off-by: NZhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/arm64/include/asm/kexec.h

@@ -97,6 +97,8 @@ static inline void crash_prepare_suspend(void) {}
 static inline void crash_post_resume(void) {}
 #endif
 
+extern bool crash_low_mem_page_map;
+
 #ifdef CONFIG_KEXEC_CORE
 extern void __init reserve_crashkernel(void);
 extern void __init reserve_crashkernel_high(void);

arch/arm64/mm/mmu.c

@@ -469,21 +469,6 @@ 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(_text);
@@ -504,7 +489,7 @@ static void __init map_mem(pgd_t *pgdp)
 	memblock_mark_nomap(kernel_start, kernel_end - kernel_start);
 
 #ifdef CONFIG_KEXEC_CORE
-	if (crash_mem_map)
+	if (crash_low_mem_page_map)
 		eflags = NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
 
 	if (crashk_res.end)

kernel/crash_core.c

@@ -321,6 +321,7 @@ int __init parse_crashkernel_low(char *cmdline,
  */
 
 #ifdef CONFIG_ARCH_WANT_RESERVE_CRASH_KERNEL
+bool crash_low_mem_page_map __initdata;
 static bool crash_high_mem_reserved __initdata;
 static struct resource crashk_res_high;
 
@@ -393,6 +394,8 @@ void __init reserve_crashkernel_high(void)
 		ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
 		if (ret || !crash_size)
 			return;
+	} else if (!crash_base) {
+		crash_low_mem_page_map = true;
 	}
 
 	crash_size = PAGE_ALIGN(crash_size);