Re: [PATCH] x86/entry/64: Fix native_load_gs_index() SWAPGS handling with IRQ state tracing enabled

[Andy Lutomirski <luto@kernel.org>]

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On Wed, Nov 29, 2017 at 9:57 AM, Andy Lutomirski <luto@kernel.org> wrote:
> On Tue, Nov 28, 2017 at 11:09 PM, Ingo Molnar <mingo@kernel.org> wrote:
>>
>> * Jarkko Nikula <jarkko.nikula@linux.intel.com> wrote:
>>
>>> Hi
>>>
>>> Suspend-to-ram and resume stopped working on v4.15-rc1 and I bisected it to
>>> commit ca37e57bbe0c ("x86/entry/64: Add missing irqflags tracing to
>>> native_load_gs_index()").
>>>

Jarkko, can you try the attached patch?  If it survives resume, can
you see if the log contains anything interesting?

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diff --git a/arch/x86/power/cpu.c b/arch/x86/power/cpu.c
index 78c61c8ecfa8..ca5d978b86a0 100644
--- a/arch/x86/power/cpu.c
+++ b/arch/x86/power/cpu.c
@@ -245,14 +245,17 @@ static void notrace __restore_processor_state(struct saved_context *ctxt)
 	asm volatile ("movw %0, %%ds" :: "r" (ctxt->ds));
 	asm volatile ("movw %0, %%es" :: "r" (ctxt->es));
 	asm volatile ("movw %0, %%fs" :: "r" (ctxt->fs));
-	load_gs_index(0xffff);
-	WARN_ON(1);
-	load_gs_index(ctxt->gs);
 	asm volatile ("movw %0, %%ss" :: "r" (ctxt->ss));
 
 	wrmsrl(MSR_FS_BASE, ctxt->fs_base);
 	wrmsrl(MSR_GS_BASE, ctxt->gs_base);
 	wrmsrl(MSR_KERNEL_GS_BASE, ctxt->gs_kernel_base);
+
+	/*
+	 * load_gs_index() potentially calls normal C code (irqflag tracing),
+	 * so it needs GSBASE restored first.
+	 */
+	load_gs_index(ctxt->gs);
 #endif
 
 	fix_processor_context();