s390x currently always results in is_kdump_kernel() == false, because
it sets "elfcorehdr_addr = ELFCORE_ADDR_MAX;" early during setup_arch to
deactivate the elfcorehdr= kernel parameter.

Let's follow the powerpc example and implement our own logic.

This is required for virtio-mem to reliably identify a kdump
environment to not try hotplugging memory.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 arch/s390/include/asm/kexec.h | 4 ++++
 arch/s390/kernel/crash_dump.c | 6 ++++++
 2 files changed, 10 insertions(+)

diff --git a/arch/s390/include/asm/kexec.h b/arch/s390/include/asm/kexec.h
index 1bd08eb56d5f..bd20543515f5 100644
--- a/arch/s390/include/asm/kexec.h
+++ b/arch/s390/include/asm/kexec.h
@@ -94,6 +94,9 @@ void arch_kexec_protect_crashkres(void);
 
 void arch_kexec_unprotect_crashkres(void);
 #define arch_kexec_unprotect_crashkres arch_kexec_unprotect_crashkres
+
+bool is_kdump_kernel(void);
+#define is_kdump_kernel is_kdump_kernel
 #endif
 
 #ifdef CONFIG_KEXEC_FILE
@@ -107,4 +110,5 @@ int arch_kexec_apply_relocations_add(struct purgatory_info *pi,
 int arch_kimage_file_post_load_cleanup(struct kimage *image);
 #define arch_kimage_file_post_load_cleanup arch_kimage_file_post_load_cleanup
 #endif
+
 #endif /*_S390_KEXEC_H */
diff --git a/arch/s390/kernel/crash_dump.c b/arch/s390/kernel/crash_dump.c
index edae13416196..cca1827d3d2e 100644
--- a/arch/s390/kernel/crash_dump.c
+++ b/arch/s390/kernel/crash_dump.c
@@ -237,6 +237,12 @@ int remap_oldmem_pfn_range(struct vm_area_struct *vma, unsigned long from,
 						       prot);
 }
 
+bool is_kdump_kernel(void)
+{
+	return oldmem_data.start && !is_ipl_type_dump();
+}
+EXPORT_SYMBOL_GPL(is_kdump_kernel);
+
 static const char *nt_name(Elf64_Word type)
 {
 	const char *name = "LINUX";
-- 
2.46.0