[PATCH v13 2/6] x86/boot: Introduce get_acpi_rsdp() to parse RSDP in cmdline from KEXEC

[Chao Fan]

Memory information in SRAT is necessary to fix the conflict between
KASLR and memory-hotremove.

ACPI SRAT (System/Static Resource Affinity Table) shows the details
about memory ranges, including ranges of memory provided by hot-added
memory devices. SRAT is introduced by Root System Description
Pointer(RSDP). So RSDP should be found firstly.

When booting form KEXEC/EFI/BIOS, the methods to find RSDP
are different. When booting from KEXEC, 'acpi_rsdp' may have been
added to cmdline, so parse cmdline to find RSDP.

Since 'RANDOMIZE_BASE' && 'MEMORY_HOTREMOVE' is needed, introduce
'CONFIG_EARLY_PARSE_RSDP' to make ifdeffery clear.

Signed-off-by: Chao Fan <fanc.fnst@xxxxxxxxxxxxxx>
---
 arch/x86/Kconfig                | 10 ++++++++++
 arch/x86/boot/compressed/acpi.c | 30 ++++++++++++++++++++++++++++++
 arch/x86/boot/compressed/misc.h |  6 ++++++
 3 files changed, 46 insertions(+)
 create mode 100644 arch/x86/boot/compressed/acpi.c

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ba7e3464ee92..455da382fa9e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2149,6 +2149,16 @@ config X86_NEED_RELOCS
 	def_bool y
 	depends on RANDOMIZE_BASE || (X86_32 && RELOCATABLE)
 
+config EARLY_PARSE_RSDP
+	bool "Parse RSDP pointer on compressed period for KASLR"
+	def_bool y
+	depends on RANDOMIZE_BASE && MEMORY_HOTREMOVE
+	help
+	  This option parses RSDP in compressed period. Works
+	  for KASLR to get memory information from SRAT table and choose
+	  immovable memory to extract kernel.
+	  Say Y if you want to use both KASLR and memory-hotremove.
+
 config PHYSICAL_ALIGN
 	hex "Alignment value to which kernel should be aligned"
 	default "0x200000"
diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c
new file mode 100644
index 000000000000..cad15686f82c
--- /dev/null
+++ b/arch/x86/boot/compressed/acpi.c
@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0
+#define BOOT_CTYPE_H
+#include "misc.h"
+#include "error.h"
+
+#include <linux/efi.h>
+#include <linux/numa.h>
+#include <linux/acpi.h>
+#include <asm/efi.h>
+
+#define STATIC
+#include <linux/decompress/mm.h>
+
+#include "../string.h"
+
+static acpi_physical_address get_acpi_rsdp(void)
+{
+#ifdef CONFIG_KEXEC
+	unsigned long long res;
+	int len = 0;
+	char val[MAX_ADDRESS_LENGTH+1];
+
+	len = cmdline_find_option("acpi_rsdp", val, MAX_ADDRESS_LENGTH+1);
+	if (len > 0) {
+		val[len] = 0;
+		return (acpi_physical_address)kstrtoull(val, 16, &res);
+	}
+	return 0;
+#endif
+}
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index a1d5918765f3..72fcfbfec3c6 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -116,3 +116,9 @@ static inline void console_init(void)
 void set_sev_encryption_mask(void);
 
 #endif
+
+/* acpi.c */
+#ifdef CONFIG_EARLY_PARSE_RSDP
+/* Max length of 64-bit hex address string is 18, prefix "0x" + 16 hex digit. */
+#define MAX_ADDRESS_LENGTH 18
+#endif
-- 
2.19.2