x86: kdump: use generic interface to simplify crashkernel reservation code

With the help of newly changed function parse_crashkernel() and generic
reserve_crashkernel_generic(), crashkernel reservation can be simplified
by steps:

1) Add a new header file <asm/crash_core.h>, and define CRASH_ALIGN,
   CRASH_ADDR_LOW_MAX, CRASH_ADDR_HIGH_MAX and
   DEFAULT_CRASH_KERNEL_LOW_SIZE in <asm/crash_core.h>;

2) Add arch_reserve_crashkernel() to call parse_crashkernel() and
   reserve_crashkernel_generic(), and do the ARCH specific work if
   needed.

3) Add ARCH_HAS_GENERIC_CRASHKERNEL_RESERVATION Kconfig in
   arch/x86/Kconfig.

When adding DEFAULT_CRASH_KERNEL_LOW_SIZE, add crash_low_size_default() to
calculate crashkernel low memory because x86_64 has special requirement.

The old reserve_crashkernel_low() and reserve_crashkernel() can be
removed.

[bhe@redhat.com: move crash_low_size_default() code into <asm/crash_core.h>]
  Link: https://lkml.kernel.org/r/ZQpeAjOmuMJBFw1/@MiWiFi-R3L-srv
Link: https://lkml.kernel.org/r/20230914033142.676708-7-bhe@redhat.com
Signed-off-by: Baoquan He <bhe@redhat.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chen Jiahao <chenjiahao16@huawei.com>
Cc: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 42 insertions, 0 deletions

diff --git a/arch/x86/include/asm/crash_core.h b/arch/x86/include/asm/crash_core.h
new file mode 100644
index 000000000000..76af98f4e801
--- /dev/null
+++ b/arch/x86/include/asm/crash_core.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _X86_CRASH_CORE_H
+#define _X86_CRASH_CORE_H
+
+/* 16M alignment for crash kernel regions */
+#define CRASH_ALIGN             SZ_16M
+
+/*
+ * Keep the crash kernel below this limit.
+ *
+ * Earlier 32-bits kernels would limit the kernel to the low 512 MB range
+ * due to mapping restrictions.
+ *
+ * 64-bit kdump kernels need to be restricted to be under 64 TB, which is
+ * the upper limit of system RAM in 4-level paging mode. Since the kdump
+ * jump could be from 5-level paging to 4-level paging, the jump will fail if
+ * the kernel is put above 64 TB, and during the 1st kernel bootup there's
+ * no good way to detect the paging mode of the target kernel which will be
+ * loaded for dumping.
+ */
+extern unsigned long swiotlb_size_or_default(void);
+
+#ifdef CONFIG_X86_32
+# define CRASH_ADDR_LOW_MAX     SZ_512M
+# define CRASH_ADDR_HIGH_MAX    SZ_512M
+#else
+# define CRASH_ADDR_LOW_MAX     SZ_4G
+# define CRASH_ADDR_HIGH_MAX    SZ_64T
+#endif
+
+# define DEFAULT_CRASH_KERNEL_LOW_SIZE crash_low_size_default()
+
+static inline unsigned long crash_low_size_default(void)
+{
+#ifdef CONFIG_X86_64
+	return max(swiotlb_size_or_default() + (8UL << 20), 256UL << 20);
+#else
+	return 0;
+#endif
+}
+
+#endif /* _X86_CRASH_CORE_H */