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Subject: Re: kexec reboot fails with extra wbinvd introduced for AME SME
To:     Dave Young <dyoung@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Yu Chen <yu.c.chen@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Juergen Gross <jgross@suse.com>,
        Tony Luck <tony.luck@intel.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Borislav Petkov <bp@alien8.de>,
        Rui Zhang <rui.zhang@intel.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Ingo Molnar <mingo@kernel.org>,
        Kexec Mailing List <kexec@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        ebiederm@redhat.com, Baoquan He <bhe@redhat.com>
References: <20171213025256.GA1913@dhcp-128-65.nay.redhat.com>
 <20171213155746.GA29572@yu-chen.sh.intel.com>
 <20171214092429.GA2004@dhcp-128-65.nay.redhat.com>
 <20180104031537.GA1819@dhcp-128-65.nay.redhat.com>
 <20180117072123.GA1866@dhcp-128-65.nay.redhat.com>
 <CA+55aFxCuz2K_kE3Huu3Ar32LVmWav__2CPL_=zs2g0devx9-Q@mail.gmail.com>
 <20180118014705.GA1812@dhcp-128-65.nay.redhat.com>
 <CA+55aFzc9eXKOdhS-ygQPbr0_N84d8iE8WbSGOWmpJXr1rvDjQ@mail.gmail.com>
 <20180118022905.GA2933@dhcp-128-65.nay.redhat.com>
From:   Tom Lendacky <thomas.lendacky@amd.com>
Message-ID: <2264b098-1c8f-6f11-9956-4e1b8cb4b309@amd.com>
Date:   Wed, 17 Jan 2018 23:14:54 -0600
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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@redhat.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