4 files changed, 41 insertions, 7 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index cff672da2486..709eb3edc6b2 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -603,9 +603,16 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         a memory unit (amount[KMG]). See also
                         Documentation/kdump/kdump.txt for an example.
 
+        crashkernel_high=size[KMG]
+                        [KNL, x86_64] range could be above 4G. Allow kernel
+                        to allocate physical memory region from top, so could
+                        be above 4G if system have more than 4G ram installed.
+                        Otherwise memory region will be allocated below 4G, if
+                        available.
+                        It will be ignored if crashkernel=X is specified.
         crashkernel_low=size[KMG]
-                        [KNL, x86_64] range under 4G. When crashkernel= is
-                        passed, kernel allocate physical memory region
+                        [KNL, x86_64] range under 4G. When crashkernel_high= is
+                        passed, kernel could allocate physical memory region
                         above 4G, that cause second kernel crash on system
                         that require some amount of low memory, e.g. swiotlb
                         requires at least 64M+32K low memory.  Kernel would
@@ -613,6 +620,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         This one let user to specify own low range under 4G
                         for second kernel instead.
                         0: to disable low allocation.
+                        It will be ignored when crashkernel_high=X is not used
+                        or memory reserved is below 4G.
 
         cs89x0_dma=     [HW,NET]
                         Format: <dma>
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 12349202cae7..a85a144f2052 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -507,11 +507,14 @@ static void __init memblock_x86_reserve_range_setup_data(void)
 /*
  * Keep the crash kernel below this limit.  On 32 bits earlier kernels
  * would limit the kernel to the low 512 MiB due to mapping restrictions.
+ * On 64bit, old kexec-tools need to under 896MiB.
  */
 #ifdef CONFIG_X86_32
-# define CRASH_KERNEL_ADDR_MAX  (512 << 20)
+# define CRASH_KERNEL_ADDR_LOW_MAX      (512 << 20)
+# define CRASH_KERNEL_ADDR_HIGH_MAX     (512 << 20)
 #else
-# define CRASH_KERNEL_ADDR_MAX  MAXMEM
+# define CRASH_KERNEL_ADDR_LOW_MAX      (896UL<<20)
+# define CRASH_KERNEL_ADDR_HIGH_MAX     MAXMEM
 #endif
 
 static void __init reserve_crashkernel_low(void)
@@ -525,6 +528,7 @@ static void __init reserve_crashkernel_low(void)
         int ret;
 
         total_low_mem = memblock_mem_size(1UL<<(32-PAGE_SHIFT));
+        /* crashkernel_low=YM */
         ret = parse_crashkernel_low(boot_command_line, total_low_mem,
                                                 &low_size, &base);
         if (ret != 0) {
@@ -569,14 +573,22 @@ static void __init reserve_crashkernel(void)
         const unsigned long long alignment = 16<<20;    /* 16M */
         unsigned long long total_mem;
         unsigned long long crash_size, crash_base;
+        bool high = false;
         int ret;
 
         total_mem = memblock_phys_mem_size();
 
+        /* crashkernel=XM */
         ret = parse_crashkernel(boot_command_line, total_mem,
                         &crash_size, &crash_base);
-        if (ret != 0 || crash_size <= 0)
-                return;
+        if (ret != 0 || crash_size <= 0) {
+                /* crashkernel_high=XM */
+                ret = parse_crashkernel_high(boot_command_line, total_mem,
+                                &crash_size, &crash_base);
+                if (ret != 0 || crash_size <= 0)
+                        return;
+                high = true;
+        }
 
         /* 0 means: find the address automatically */
         if (crash_base <= 0) {
@@ -584,7 +596,9 @@ static void __init reserve_crashkernel(void)
                  *  kexec want bzImage is below CRASH_KERNEL_ADDR_MAX
                  */
                 crash_base = memblock_find_in_range(alignment,
-                               CRASH_KERNEL_ADDR_MAX, crash_size, alignment);
+                                        high ? CRASH_KERNEL_ADDR_HIGH_MAX :
+                                               CRASH_KERNEL_ADDR_LOW_MAX,
+                                        crash_size, alignment);
 
                 if (!crash_base) {
                         pr_info("crashkernel reservation failed - No suitable area found.\n");
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index d2e6927bbaae..d78d28a733b1 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -200,6 +200,8 @@ extern size_t vmcoreinfo_max_size;
 
 int __init parse_crashkernel(char *cmdline, unsigned long long system_ram,
                 unsigned long long *crash_size, unsigned long long *crash_base);
+int parse_crashkernel_high(char *cmdline, unsigned long long system_ram,
+                unsigned long long *crash_size, unsigned long long *crash_base);
 int parse_crashkernel_low(char *cmdline, unsigned long long system_ram,
                 unsigned long long *crash_size, unsigned long long *crash_base);
 int crash_shrink_memory(unsigned long new_size);
diff --git a/kernel/kexec.c b/kernel/kexec.c
index bddd3d7a74b6..1b2f73f5f9b9 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -1422,6 +1422,15 @@ int __init parse_crashkernel(char *cmdline,
                                         "crashkernel=");
 }
 
+int __init parse_crashkernel_high(char *cmdline,
+                             unsigned long long system_ram,
+                             unsigned long long *crash_size,
+                             unsigned long long *crash_base)
+{
+        return __parse_crashkernel(cmdline, system_ram, crash_size, crash_base,
+                                        "crashkernel_high=");
+}
+
 int __init parse_crashkernel_low(char *cmdline,
                              unsigned long long system_ram,
                              unsigned long long *crash_size,