linux-kernel - Re: [PATCH v2] Fix undefined operation VMXOFF during reboot and crash

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Message-ID: <1593470801.608531492@apps.rackspace.com>
Date:   Mon, 29 Jun 2020 18:46:41 -0400 (EDT)
From:   "David P. Reed" <dpreed@...pplum.com>
To:     "Sean Christopherson" <sean.j.christopherson@...el.com>
Cc:     "Andy Lutomirski" <luto@...capital.net>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
        "X86 ML" <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        "Allison Randal" <allison@...utok.net>,
        "Enrico Weigelt" <info@...ux.net>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Kate Stewart" <kstewart@...uxfoundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        "Randy Dunlap" <rdunlap@...radead.org>,
        "Martin Molnar" <martin.molnar.programming@...il.com>,
        "Andy Lutomirski" <luto@...nel.org>,
        "Alexandre Chartre" <alexandre.chartre@...cle.com>,
        "Jann Horn" <jannh@...gle.com>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "LKML" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] Fix undefined operation VMXOFF during reboot and crash



On Monday, June 29, 2020 5:49pm, "Sean Christopherson" <sean.j.christopherson@...el.com> said:

> On Mon, Jun 29, 2020 at 02:22:45PM -0700, Andy Lutomirski wrote:
>>
>>
>> > On Jun 29, 2020, at 1:54 PM, David P. Reed <dpreed@...pplum.com> wrote:
>> >
>> > Simple question for those on the To: and CC: list here. Should I
>> > abandon any hope of this patch being accepted? It's been a long time.
>> >
>> > The non-response after I acknowledged that this was discovered by when
>> > working on a personal, non-commercial research project - which is
>> > "out-of-tree" (apparently dirty words on LKML) has me thinking my
>> > contribution is unwanted. That's fine, I suppose. I can maintain this patch
>> > out-of-tree as well.  I did incorporate all the helpful suggestions I
>> > received in this second patch, and given some encouragement, will happily
>> > submit a revised v3 if there is any likelihood of acceptance. I'm wary of
>> > doing more radical changes (like combining emergency and normal paths).
>> >
>>
>> Sorry about being slow and less actively encouraging than we should be. We
>> absolutely welcome personal contributions. The actual problem is that
>> everyone is worked and we’re all slow. Also, you may be hitting a corner
>> case
>> in the process: is this a KVM patch or an x86 patch?
> 
> It's an x86 patch as it's not KVM specific, e.g. this code also helps play
> nice with out of tree hypervisors.
> 
> The code change is mostly good, but it needs to be split up as there are
> three separate fixes:
> 
>   1. Handle #UD on VMXON due to a race.
>   2. Mark memory and flags as clobbered by VMXON.
>   3. Change emergency_vmx_disable_all() to not manually check cpu_vmx_enabled().
> 
> Yes, the changes are tiny, but if for example #3 introduces a bug then we
> don't have to revert #1 and #2.  Or perhaps older kernels are only subject
> to the #1 and #2 and thus dumping all three changes into a single patch makes
> it all harder to backport.  In other words, all the usual "one change per
> patch" reasons.
> 
Thanks. If no one else responds with additional suggestions, I will make it into 3 patches.
I'm happy to learn the nuances of the kernel patch regimen.