linux-kernel - Re: kexec reboot fails with extra wbinvd introduced for AME SME

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Message-ID: <2264b098-1c8f-6f11-9956-4e1b8cb4b309@amd.com>
Date:   Wed, 17 Jan 2018 23:14:54 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Dave Young <dyoung@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Yu Chen <yu.c.chen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Juergen Gross <jgross@...e.com>,
        Tony Luck <tony.luck@...el.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Borislav Petkov <bp@...en8.de>,
        Rui Zhang <rui.zhang@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Ingo Molnar <mingo@...nel.org>,
        Kexec Mailing List <kexec@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ebiederm@...hat.com, Baoquan He <bhe@...hat.com>
Subject: Re: kexec reboot fails with extra wbinvd introduced for AME SME

On 1/17/2018 8:29 PM, Dave Young wrote:
> On 01/17/18 at 06:14pm, Linus Torvalds wrote:
>> On Wed, Jan 17, 2018 at 5:47 PM, Dave Young <dyoung@...hat.com> wrote:
>>>
>>> It does not work with just once wbinvd(), and it only works with
>>> removing the wbinvd() for me.  Tom's new post works for me as well
>>> since my cpu is an Intel i5-4200U.
>>
>> Intriguing.
>>
>> It's not like the wbinvd really should be that much of a deal.
>>
>> I think Tom's patch is fine and should be applied, but it does worry
>> me a bit that even a single wbinvd makes that much of a difference for
>> you. There is very little logical reason I can think of that a wbinvd
>> should make any difference what-so-ever on an i5-4200U.
>>
>> I wonder if you have some system issues, and wbinvd just happens to
>> trigger them. But I think we do wbinvd before a suspend-to-RAM too
>> (it's "ACPI_FLUSH_CPU_CACHE()" in the ACPI code). And the dmr code
>> dioes "wbinvd_on_all_cpus()" which does a cross-call etc.
>>
>> Would you mind experimenting a bit with that wbinvd?
>>
>> In particular, what happens if you enable it (so it's not hidden by
>> the SME check), but you move it up to before interrupts are disabled?
> 
> Will play with it more.  Actually I found the hang seems happens
> in code of arch/x86/kernel/relocate_kernel_64.S, there is another
> wbinvd there as well.

The wbinvd in arch/x86/kernel/relocate_kernel_64.S is only performed if
SME is active, so that one won't be executed on an Intel chip.

Thanks,
Tom

> 
>>
>> I'm wondering if there is some issue with MCE generation and wbinvd
>> and whatever, and doing it when the CPU is down and interrupts are
>> disabled causes some system issue..
>>
>> Does anybody have any other ideas?
>>
>>                 Linus