4 files changed, 75 insertions, 7 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 363e348bff9b..da0e0773ca96 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -594,6 +594,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
                         is selected automatically. Check
                         Documentation/kdump/kdump.txt for further details.
 
+        crashkernel_low=size[KMG]
+                        [KNL, x86] parts under 4G.
+
         crashkernel=range1:size1[,range2:size2,...][@offset]
                         [KNL] Same as above, but depends on the memory
                         in the running system. The syntax of range is
diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 4778ddeedc8a..5dc47c3e537b 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -508,8 +508,44 @@ static void __init memblock_x86_reserve_range_setup_data(void)
 # define CRASH_KERNEL_ADDR_MAX  MAXMEM
 #endif
 
+static void __init reserve_crashkernel_low(void)
+{
+#ifdef CONFIG_X86_64
+        const unsigned long long alignment = 16<<20;    /* 16M */
+        unsigned long long low_base = 0, low_size = 0;
+        unsigned long total_low_mem;
+        unsigned long long base;
+        int ret;
+
+        total_low_mem = memblock_mem_size(1UL<<(32-PAGE_SHIFT));
+        ret = parse_crashkernel_low(boot_command_line, total_low_mem,
+                                                &low_size, &base);
+        if (ret != 0 || low_size <= 0)
+                return;
+
+        low_base = memblock_find_in_range(low_size, (1ULL<<32),
+                                        low_size, alignment);
+
+        if (!low_base) {
+                pr_info("crashkernel low reservation failed - No suitable area found.\n");
+
+                return;
+        }
+
+        memblock_reserve(low_base, low_size);
+        pr_info("Reserving %ldMB of low memory at %ldMB for crashkernel (System low RAM: %ldMB)\n",
+                        (unsigned long)(low_size >> 20),
+                        (unsigned long)(low_base >> 20),
+                        (unsigned long)(total_low_mem >> 20));
+        crashk_low_res.start = low_base;
+        crashk_low_res.end   = low_base + low_size - 1;
+        insert_resource(&iomem_resource, &crashk_low_res);
+#endif
+}
+
 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;
         int ret;
@@ -523,8 +559,6 @@ static void __init reserve_crashkernel(void)
 
         /* 0 means: find the address automatically */
         if (crash_base <= 0) {
-                const unsigned long long alignment = 16<<20;    /* 16M */
-
                 /*
                  *  kexec want bzImage is below CRASH_KERNEL_ADDR_MAX
                  */
@@ -535,6 +569,7 @@ static void __init reserve_crashkernel(void)
                         pr_info("crashkernel reservation failed - No suitable area found.\n");
                         return;
                 }
+
         } else {
                 unsigned long long start;
 
@@ -556,6 +591,9 @@ static void __init reserve_crashkernel(void)
         crashk_res.start = crash_base;
         crashk_res.end   = crash_base + crash_size - 1;
         insert_resource(&iomem_resource, &crashk_res);
+
+        if (crash_base >= (1ULL<<32))
+                reserve_crashkernel_low();
 }
 #else
 static void __init reserve_crashkernel(void)
diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index d0b8458a703a..d2e6927bbaae 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -191,6 +191,7 @@ extern struct kimage *kexec_crash_image;
 /* Location of a reserved region to hold the crash kernel.
  */
 extern struct resource crashk_res;
+extern struct resource crashk_low_res;
 typedef u32 note_buf_t[KEXEC_NOTE_BYTES/4];
 extern note_buf_t __percpu *crash_notes;
 extern u32 vmcoreinfo_note[VMCOREINFO_NOTE_SIZE/4];
@@ -199,6 +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_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);
 size_t crash_get_memory_size(void);
 void crash_free_reserved_phys_range(unsigned long begin, unsigned long end);
diff --git a/kernel/kexec.c b/kernel/kexec.c
index 5e4bd7864c5d..2436ffcec91f 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -54,6 +54,12 @@ struct resource crashk_res = {
         .end   = 0,
         .flags = IORESOURCE_BUSY | IORESOURCE_MEM
 };
+struct resource crashk_low_res = {
+        .name  = "Crash kernel low",
+        .start = 0,
+        .end   = 0,
+        .flags = IORESOURCE_BUSY | IORESOURCE_MEM
+};
 
 int kexec_should_crash(struct task_struct *p)
 {
@@ -1369,10 +1375,11 @@ static int __init parse_crashkernel_simple(char 		*cmdline,
  * That function is the entry point for command line parsing and should be
  * called from the arch-specific code.
  */
-int __init parse_crashkernel(char                *cmdline,
+static int __init __parse_crashkernel(char *cmdline,
                              unsigned long long system_ram,
                              unsigned long long *crash_size,
-                             unsigned long long *crash_base)
+                             unsigned long long *crash_base,
+                                const char *name)
 {
         char    *p = cmdline, *ck_cmdline = NULL;
         char    *first_colon, *first_space;
@@ -1382,16 +1389,16 @@ int __init parse_crashkernel(char 		 *cmdline,
         *crash_base = 0;
 
         /* find crashkernel and use the last one if there are more */
-        p = strstr(p, "crashkernel=");
+        p = strstr(p, name);
         while (p) {
                 ck_cmdline = p;
-                p = strstr(p+1, "crashkernel=");
+                p = strstr(p+1, name);
         }
 
         if (!ck_cmdline)
                 return -EINVAL;
 
-        ck_cmdline += 12; /* strlen("crashkernel=") */
+        ck_cmdline += strlen(name);
 
         /*
          * if the commandline contains a ':', then that's the extended
@@ -1409,6 +1416,23 @@ int __init parse_crashkernel(char 		 *cmdline,
         return 0;
 }
 
+int __init parse_crashkernel(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=");
+}
+
+int __init parse_crashkernel_low(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_low=");
+}
 
 static void update_vmcoreinfo_note(void)
 {