x86, gdt, hibernate: Store/load GDT for hibernate path.

The git commite7a5cd063c7b4c58417f674821d63f5eb6747e37
("x86-64, gdt: Store/load GDT for ACPI S3 or hibernate/resume path
is not needed.") assumes that for the hibernate path the booting
kernel and the resuming kernel MUST be the same. That is certainly
the case for a 32-bit kernel (see check_image_kernel and
CONFIG_ARCH_HIBERNATION_HEADER config option).

However for 64-bit kernels it is OK to have a different kernel
version (and size of the image) of the booting and resuming kernels.
Hence the above mentioned git commit introduces an regression.

This patch fixes it by introducing a 'struct desc_ptr gdt_desc'
back in the 'struct saved_context'. However instead of having in the
'save_processor_state' and 'restore_processor_state' the
store/load_gdt calls, we are only saving the GDT in the
save_processor_state.

For the restore path the lgdt operation is done in
hibernate_asm_[32|64].S in the 'restore_registers' path.

The apt reader of this description will recognize that only 64-bit
kernels need this treatment, not 32-bit. This patch adds the logic
in the 32-bit path to be more similar to 64-bit so that in the future
the unification process can take advantage of this.

[ hpa: this also reverts an inadvertent on-disk format change ]

Suggested-by: "H. Peter Anvin" <[e-mail]>
Acked-by: "Rafael J. Wysocki" <[e-mail]>
Signed-off-by: Konrad Rzeszutek Wilk <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: H. Peter Anvin <[e-mail]>

arch/x86/include/asm/suspend_32.h

···
 	unsigned long cr0, cr2, cr3, cr4;
 	u64 misc_enable;
 	bool misc_enable_saved;
+	struct desc_ptr gdt_desc;
 	struct desc_ptr idt;
 	u16 ldt;
 	u16 tss;

arch/x86/include/asm/suspend_64.h

···
 	u64 misc_enable;
 	bool misc_enable_saved;
 	unsigned long efer;
+	u16 gdt_pad; /* Unused */
+	struct desc_ptr gdt_desc;
 	u16 idt_pad;
 	u16 idt_limit;
 	unsigned long idt_base;

arch/x86/kernel/asm-offsets_32.c

···
 	OFFSET(IA32_RT_SIGFRAME_sigcontext, rt_sigframe, uc.uc_mcontext);
 	BLANK();
 
+	OFFSET(saved_context_gdt_desc, saved_context, gdt_desc);
+	BLANK();
+
 	/* Offset from the sysenter stack to tss.sp0 */
 	DEFINE(TSS_sysenter_sp0, offsetof(struct tss_struct, x86_tss.sp0) -
 		 sizeof(struct tss_struct));

arch/x86/kernel/asm-offsets_64.c

···
 	ENTRY(cr3);
 	ENTRY(cr4);
 	ENTRY(cr8);
+	ENTRY(gdt_desc);
 	BLANK();
 #undef ENTRY
 

arch/x86/power/cpu.c

···
 #include <asm/cpu.h>
 
 #ifdef CONFIG_X86_32
-static struct saved_context saved_context;
-
 unsigned long saved_context_ebx;
 unsigned long saved_context_esp, saved_context_ebp;
 unsigned long saved_context_esi, saved_context_edi;
 unsigned long saved_context_eflags;
-#else
-/* CONFIG_X86_64 */
-struct saved_context saved_context;
 #endif
+struct saved_context saved_context;
 
 /**
  *	__save_processor_state - save CPU registers before creating a
···
 /* CONFIG_X86_64 */
 	store_idt((struct desc_ptr *)&ctxt->idt_limit);
 #endif
+	/*
+	 * We save it here, but restore it only in the hibernate case.
+	 * For ACPI S3 resume, this is loaded via 'early_gdt_desc' in 64-bit
+	 * mode in "secondary_startup_64". In 32-bit mode it is done via
+	 * 'pmode_gdt' in wakeup_start.
+	 */
+	ctxt->gdt_desc.size = GDT_SIZE - 1;
+	ctxt->gdt_desc.address = (unsigned long)get_cpu_gdt_table(smp_processor_id());
+
 	store_tr(ctxt->tr);
 
 	/* XMM0..XMM15 should be handled by kernel_fpu_begin(). */

arch/x86/power/hibernate_asm_32.S

···
 	pushl saved_context_eflags
 	popfl
 
+	/* Saved in save_processor_state. */
+	movl $saved_context, %eax
+	lgdt saved_context_gdt_desc(%eax)
+
 	xorl	%eax, %eax
 
 	ret

arch/x86/power/hibernate_asm_64.S

···
 	pushq	pt_regs_flags(%rax)
 	popfq
 
+	/* Saved in save_processor_state. */
+	lgdt	saved_context_gdt_desc(%rax)
+
 	xorq	%rax, %rax
 
 	/* tell the hibernation core that we've just restored the memory */