[PATCH 1/2] x86/setup: consolidate early memory reservations

[Mike Rapoport <rppt@kernel.org>]

From: Mike Rapoport <rppt@linux.ibm.com>

The early reservations of memory areas used by the firmware, bootloader,
kernel text and data are spread over setup_arch(). Moreover, some of them
happen *after* memblock allocations, e.g trim_platform_memory_ranges() and
trim_low_memory_range() are called after reserve_real_mode() that allocates
memory.

We did not observe corruption of these memory regions because memblock
always allocates memory either from the end of memory (in top-down mode) or
above the kernel image (in bottom-up mode). However, the bottom up mode is
going to be updated to span the entire memory [1] to avoid limitations
caused by KASLR.

Consolidate early memory reservations in a dedicated function to improve
robustness against future changes. Having the early reservations in one
place also makes it clearer what memory must be reserved before we allow
memblock allocations.

[1] https://lore.kernel.org/lkml/20201217201214.3414100-2-guro@fb.com

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---
 arch/x86/kernel/setup.c | 80 ++++++++++++++++++++++-------------------
 1 file changed, 44 insertions(+), 36 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 3412c4595efd..32cd2e790a0a 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -728,7 +728,38 @@ static void __init trim_low_memory_range(void)
 	 */
 	memblock_reserve(0, ALIGN(reserve_low, PAGE_SIZE));
 }
-	
+
+static void __init early_reserve_memory(void)
+{
+	/*
+	 * Reserve the memory occupied by the kernel between _text and
+	 * __end_of_kernel_reserve symbols. Any kernel sections after the
+	 * __end_of_kernel_reserve symbol must be explicitly reserved with a
+	 * separate memblock_reserve() or they will be discarded.
+	 */
+	memblock_reserve(__pa_symbol(_text),
+			 (unsigned long)__end_of_kernel_reserve - (unsigned long)_text);
+
+	/*
+	 * Make sure page 0 is always reserved because on systems with
+	 * L1TF its contents can be leaked to user processes.
+	 */
+	memblock_reserve(0, PAGE_SIZE);
+
+	early_reserve_initrd();
+
+	if (efi_enabled(EFI_BOOT))
+		efi_memblock_x86_reserve_range();
+
+	memblock_x86_reserve_range_setup_data();
+
+	reserve_ibft_region();
+	reserve_bios_regions();
+
+	trim_platform_memory_ranges();
+	trim_low_memory_range();
+}
+
 /*
  * Dump out kernel offset information on panic.
  */
@@ -763,29 +794,6 @@ dump_kernel_offset(struct notifier_block *self, unsigned long v, void *p)
 
 void __init setup_arch(char **cmdline_p)
 {
-	/*
-	 * Reserve the memory occupied by the kernel between _text and
-	 * __end_of_kernel_reserve symbols. Any kernel sections after the
-	 * __end_of_kernel_reserve symbol must be explicitly reserved with a
-	 * separate memblock_reserve() or they will be discarded.
-	 */
-	memblock_reserve(__pa_symbol(_text),
-			 (unsigned long)__end_of_kernel_reserve - (unsigned long)_text);
-
-	/*
-	 * Make sure page 0 is always reserved because on systems with
-	 * L1TF its contents can be leaked to user processes.
-	 */
-	memblock_reserve(0, PAGE_SIZE);
-
-	early_reserve_initrd();
-
-	/*
-	 * At this point everything still needed from the boot loader
-	 * or BIOS or kernel text should be early reserved or marked not
-	 * RAM in e820. All other memory is free game.
-	 */
-
 #ifdef CONFIG_X86_32
 	memcpy(&boot_cpu_data, &new_cpu_data, sizeof(new_cpu_data));
 
@@ -909,8 +917,18 @@ void __init setup_arch(char **cmdline_p)
 
 	parse_early_param();
 
-	if (efi_enabled(EFI_BOOT))
-		efi_memblock_x86_reserve_range();
+	/*
+	 * Do some memory reservations *before* memory is added to
+	 * memblock, so memblock allocations won't overwrite it.
+	 * Do it after early param, so we could get (unlikely) panic from
+	 * serial.
+	 *
+	 * After this point everything still needed from the boot loader or
+	 * firmware or kernel text should be early reserved or marked not
+	 * RAM in e820. All other memory is free game.
+	 */
+	early_reserve_memory();
+
 #ifdef CONFIG_MEMORY_HOTPLUG
 	/*
 	 * Memory used by the kernel cannot be hot-removed because Linux
@@ -937,9 +955,6 @@ void __init setup_arch(char **cmdline_p)
 
 	x86_report_nx();
 
-	/* after early param, so could get panic from serial */
-	memblock_x86_reserve_range_setup_data();
-
 	if (acpi_mps_check()) {
 #ifdef CONFIG_X86_LOCAL_APIC
 		disable_apic = 1;
@@ -1031,8 +1046,6 @@ void __init setup_arch(char **cmdline_p)
 	 */
 	find_smp_config();
 
-	reserve_ibft_region();
-
 	early_alloc_pgt_buf();
 
 	/*
@@ -1053,8 +1066,6 @@ void __init setup_arch(char **cmdline_p)
 	 */
 	sev_setup_arch();
 
-	reserve_bios_regions();
-
 	efi_fake_memmap();
 	efi_find_mirror();
 	efi_esrt_init();
@@ -1080,9 +1091,6 @@ void __init setup_arch(char **cmdline_p)
 
 	reserve_real_mode();
 
-	trim_platform_memory_ranges();
-	trim_low_memory_range();
-
 	init_mem_mapping();
 
 	idt_setup_early_pf();
-- 
2.28.0