x86/power: Make restore_processor_context() sane

My previous attempt to fix a couple of bugs in __restore_processor_context():

  5b06bbcfc2c6 ("x86/power: Fix some ordering bugs in __restore_processor_context()")

... introduced yet another bug, breaking suspend-resume.

Rather than trying to come up with a minimal fix, let's try to clean it up
for real.  This patch fixes quite a few things:

 - The old code saved a nonsensical subset of segment registers.
   The only registers that need to be saved are those that contain
   userspace state or those that can't be trivially restored without
   percpu access working.  (On x86_32, we can restore percpu access
   by writing __KERNEL_PERCPU to %fs.  On x86_64, it's easier to
   save and restore the kernel's GSBASE.)  With this patch, we
   restore hardcoded values to the kernel state where applicable and
   explicitly restore the user state after fixing all the descriptor
   tables.

 - We used to use an unholy mix of inline asm and C helpers for
   segment register access.  Let's get rid of the inline asm.

This fixes the reported s2ram hangs and make the code all around
more logical.

Analyzed-by: Linus Torvalds <torvalds@linux-foundation.org>
Reported-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reported-by: Pavel Machek <pavel@ucw.cz>
Tested-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Tested-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: Zhang Rui <rui.zhang@intel.com>
Fixes: 5b06bbcfc2c6 ("x86/power: Fix some ordering bugs in __restore_processor_context()")
Link: http://lkml.kernel.org/r/398ee68e5c0f766425a7b746becfc810840770ff.1513286253.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 21 insertions, 3 deletions

diff --git a/arch/x86/include/asm/suspend_32.h b/arch/x86/include/asm/suspend_32.h
index 982c325dad33..8be6afb58471 100644
--- a/arch/x86/include/asm/suspend_32.h
+++ b/arch/x86/include/asm/suspend_32.h
@@ -12,7 +12,13 @@
 
 /* image of the saved processor state */
 struct saved_context {
-	u16 es, fs, gs, ss;
+	/*
+	 * On x86_32, all segment registers, with the possible exception of
+	 * gs, are saved at kernel entry in pt_regs.
+	 */
+#ifdef CONFIG_X86_32_LAZY_GS
+	u16 gs;
+#endif
 	unsigned long cr0, cr2, cr3, cr4;
 	u64 misc_enable;
 	bool misc_enable_saved;
diff --git a/arch/x86/include/asm/suspend_64.h b/arch/x86/include/asm/suspend_64.h
index 600e9e0aea51..a7af9f53c0cb 100644
--- a/arch/x86/include/asm/suspend_64.h
+++ b/arch/x86/include/asm/suspend_64.h
@@ -20,8 +20,20 @@
  */
 struct saved_context {
 	struct pt_regs regs;
-	u16 ds, es, fs, gs, ss;
-	unsigned long gs_base, gs_kernel_base, fs_base;
+
+	/*
+	 * User CS and SS are saved in current_pt_regs().  The rest of the
+	 * segment selectors need to be saved and restored here.
+	 */
+	u16 ds, es, fs, gs;
+
+	/*
+	 * Usermode FSBASE and GSBASE may not match the fs and gs selectors,
+	 * so we save them separately.  We save the kernelmode GSBASE to
+	 * restore percpu access after resume.
+	 */
+	unsigned long kernelmode_gs_base, usermode_gs_base, fs_base;
+
 	unsigned long cr0, cr2, cr3, cr4, cr8;
 	u64 misc_enable;
 	bool misc_enable_saved;