1 files changed, 48 insertions, 0 deletions

diff --git a/arch/x86/lib/acpi_s3.c b/arch/x86/lib/acpi_s3.c
index 0b62b75908..3175da828b 100644
--- a/arch/x86/lib/acpi_s3.c
+++ b/arch/x86/lib/acpi_s3.c
@@ -9,6 +9,8 @@
 #include <asm/acpi_table.h>
 #include <asm/post.h>
 
+DECLARE_GLOBAL_DATA_PTR;
+
 static void asmlinkage (*acpi_do_wakeup)(void *vector) = (void *)WAKEUP_BASE;
 
 static void acpi_jump_to_wakeup(void *vector)
@@ -29,6 +31,52 @@ void acpi_resume(struct acpi_fadt *fadt)
 
 	wake_vec = acpi_find_wakeup_vector(fadt);
 
+	/*
+	 * Restore the memory content starting from address 0x1000 which is
+	 * used for the real mode interrupt handler stubs.
+	 */
+	memcpy((void *)0x1000, (const void *)gd->arch.backup_mem,
+	       S3_RESERVE_SIZE);
+
 	post_code(POST_OS_RESUME);
 	acpi_jump_to_wakeup(wake_vec);
 }
+
+int acpi_s3_reserve(void)
+{
+	/* adjust stack pointer for ACPI S3 resume backup memory */
+	gd->start_addr_sp -= S3_RESERVE_SIZE;
+	gd->arch.backup_mem = gd->start_addr_sp;
+
+	gd->start_addr_sp &= ~0xf;
+
+	/*
+	 * U-Boot sets up the real mode interrupt handler stubs starting from
+	 * address 0x1000. In most cases, the first 640K (0x00000 - 0x9ffff)
+	 * system memory is reported as system RAM in E820 table to the OS.
+	 * (see install_e820_map() implementation for each platform). So OS
+	 * can use these memories whatever it wants.
+	 *
+	 * If U-Boot is in an S3 resume path, care must be taken not to corrupt
+	 * these memorie otherwise OS data gets lost. Testing shows that, on
+	 * Microsoft Windows 10 on Intel Baytrail its wake up vector happens to
+	 * be installed at the same address 0x1000. While on Linux its wake up
+	 * vector does not overlap this memory range, but after resume kernel
+	 * checks low memory range per config option CONFIG_X86_RESERVE_LOW
+	 * which is 64K by default to see whether a memory corruption occurs
+	 * during the suspend/resume (it's harmless, but warnings are shown
+	 * in the kernel dmesg logs).
+	 *
+	 * We cannot simply mark the these memory as reserved in E820 table
+	 * because such configuration makes GRUB complain: unable to allocate
+	 * real mode page. Hence we choose to back up these memories to the
+	 * place where we reserved on our stack for our S3 resume work.
+	 * Before jumping to OS wake up vector, we need restore the original
+	 * content there (see acpi_resume() above).
+	 */
+	if (gd->arch.prev_sleep_state == ACPI_S3)
+		memcpy((void *)gd->arch.backup_mem, (const void *)0x1000,
+		       S3_RESERVE_SIZE);
+
+	return 0;
+}