From: Andy Lutomirski <luto@kernel.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Jarkko Nikula <jarkko.nikula@linux.intel.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
Linus Torvalds <torvalds@linux-foundation.org>,
Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH] x86/entry/64: Fix native_load_gs_index() SWAPGS handling with IRQ state tracing enabled
Date: Wed, 29 Nov 2017 09:57:43 -0800 [thread overview]
Message-ID: <CALCETrXwM7syieKz8CcFE8qHL6r_yA0jP49A1EJsw5UNWz+UNA@mail.gmail.com> (raw)
In-Reply-To: <20171129070951.hjjjpbyilzaak4ig@gmail.com>
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()").
>>
>> I noticed it on Intel Kabylake (core) and Apollolake (atom) based prototype
>> machines. Symptoms are that machine appears to enter into suspend but
>> resumes instantly and hangs. Unfortunately no logs.
>>
>> If I revert ca37e57bbe0c on v4.15-rc1 it works as expected.
>
> Hm, that commit looks broken with irq-tracing enabled.
> Does the patch below fix it?
>
> In fact the exception handler itself appears to have broken GS handling as well -
> I suspect it never triggers in practice, because it was broken forever.
>
> Andy, do you concur?
No.
>
> On a related note, we should definitely extend the 'intended GS state' annotation
> comments I did in this patch to all SWAPGS instances - this way code review has a
> much higher chance of finding discrepancies between intent and actual code.
Agreed. I'll send a patch.
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -945,16 +945,16 @@ idtentry simd_coprocessor_error do_simd_coprocessor_error has_error_code=0
> */
> ENTRY(native_load_gs_index)
> FRAME_BEGIN
> + SWAPGS /* switch from user GS to kernel GS */
No, we start with kernel GS. It was correct before.
> pushfq
> DISABLE_INTERRUPTS(CLBR_ANY & ~CLBR_RDI)
> TRACE_IRQS_OFF
> - SWAPGS
> .Lgs_change:
> movl %edi, %gs
> 2: ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_FENCE
> - SWAPGS
> TRACE_IRQS_FLAGS (%rsp)
> popfq
> + SWAPGS /* switch from kernel GS to user GS */
> FRAME_END
> ret
> ENDPROC(native_load_gs_index)
> @@ -964,7 +964,7 @@ EXPORT_SYMBOL(native_load_gs_index)
> .section .fixup, "ax"
> /* running with kernelgs */
> bad_gs:
> - SWAPGS /* switch back to user gs */
> + SWAPGS /* switch back to user GS, to modify GS */
> .macro ZAP_GS
> /* This can't be a string because the preprocessor needs to see it. */
> movl $__USER_DS, %eax
> @@ -973,6 +973,7 @@ EXPORT_SYMBOL(native_load_gs_index)
> ALTERNATIVE "", "ZAP_GS", X86_BUG_NULL_SEG
> xorl %eax, %eax
> movl %eax, %gs
> + SWAPGS /* switch to kernel GS again before continuing */
Which we don't want to do because the landing site expects user GS.
I suspect we're hitting an entirely different bug, that we're blowing
up if we WARN too early in resume.
next prev parent reply other threads:[~2017-11-29 17:58 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-28 14:35 Suspend-to-ram/resume regression with commit ca37e57bbe0c Jarkko Nikula
2017-11-29 7:09 ` [PATCH] x86/entry/64: Fix native_load_gs_index() SWAPGS handling with IRQ state tracing enabled Ingo Molnar
2017-11-29 9:25 ` Jarkko Nikula
2017-11-29 9:28 ` Thomas Gleixner
2017-11-29 12:39 ` Jarkko Nikula
2017-11-29 12:47 ` Peter Zijlstra
2017-11-29 14:33 ` Andy Lutomirski
2017-11-29 14:56 ` David Laight
2017-11-29 16:22 ` Andy Lutomirski
2017-11-29 16:51 ` David Laight
2017-11-29 20:48 ` Linus Torvalds
2017-11-29 16:51 ` Andy Lutomirski
2017-11-29 17:57 ` Andy Lutomirski [this message]
2017-11-29 18:08 ` Peter Zijlstra
2017-11-29 18:12 ` Andy Lutomirski
2017-11-29 20:58 ` Linus Torvalds
2017-11-29 21:25 ` Andy Lutomirski
2017-11-29 21:41 ` Andy Lutomirski
2017-11-29 21:57 ` Andy Lutomirski
2017-11-30 8:42 ` Jarkko Nikula
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