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Date:   Sun, 5 Jul 2020 15:52:08 -0400 (EDT)
Subject: Re: [PATCH v3 2/3] Fix undefined operation fault that can hang a cpu on crash or panic
From:   "David P. Reed" <dpreed@deepplum.com>
To:     "Andy Lutomirski" <luto@kernel.org>
Cc:     "Sean Christopherson" <sean.j.christopherson@intel.com>,
        "Thomas Gleixner" <tglx@linutronix.de>,
        "Ingo Molnar" <mingo@redhat.com>, "Borislav Petkov" <bp@alien8.de>,
        "X86 ML" <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        "Allison Randal" <allison@lohutok.net>,
        "Enrico Weigelt" <info@metux.net>,
        "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
        "Kate Stewart" <kstewart@linuxfoundation.org>,
        "=?utf-8?Q?Peter_Zijlstra_=28Intel=29?=" <peterz@infradead.org>,
        "Randy Dunlap" <rdunlap@infradead.org>,
        "Martin Molnar" <martin.molnar.programming@gmail.com>,
        "Andy Lutomirski" <luto@kernel.org>,
        "Alexandre Chartre" <alexandre.chartre@oracle.com>,
        "Jann Horn" <jannh@google.com>,
        "Dave Hansen" <dave.hansen@linux.intel.com>,
        "LKML" <linux-kernel@vger.kernel.org>
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Thanks, will handle these. 2 questions below.=0A=0AOn Sunday, July 5, 2020 =
2:22pm, "Andy Lutomirski" <luto@kernel.org> said:=0A=0A> On Sat, Jul 4, 202=
0 at 1:38 PM David P. Reed <dpreed@deepplum.com> wrote:=0A>>=0A>> Fix: Mask=
 undefined operation fault during emergency VMXOFF that must be=0A>> attemp=
ted to force cpu exit from VMX root operation.=0A>> Explanation: When a cpu=
 may be in VMX root operation (only possible when=0A>> CR4.VMXE is set), cr=
ash or panic reboot tries to exit VMX root operation=0A>> using VMXOFF. Thi=
s is necessary, because any INIT will be masked while cpu=0A>> is in VMX ro=
ot operation, but that state cannot be reliably=0A>> discerned by the state=
 of the cpu.=0A>> VMXOFF faults if the cpu is not actually in VMX root oper=
ation, signalling=0A>> undefined operation.=0A>> Discovered while debugging=
 an out-of-tree x-visor with a race. Can happen=0A>> due to certain kinds o=
f bugs in KVM.=0A> =0A> Can you re-wrap lines to 68 characters?  Also, the =
Fix: and=0A=0AI used 'scripts/checkpatch.pl' and it had me wrap to 75 chars=
:=0A"WARNING: Possible unwrapped commit description (prefer a maximum 75 ch=
ars per line)"=0A=0AShould I submit a fix to checkpatch.pl to say 68? =0A=
=0A> Explanation: is probably unnecessary.  You could say:=0A> =0A> Ignore =
a potential #UD failut during emergency VMXOFF ...=0A> =0A> When a cpu may =
be in VMX ...=0A> =0A>>=0A>> Fixes: 208067 <https://bugzilla.kernel.org/sho=
w_bug.cgi?id=3D208067>=0A>> Reported-by: David P. Reed <dpreed@deepplum.com=
>=0A> =0A> It's not really necessary to say that you, the author, reported =
the=0A> problem, but I guess it's harmless.=0A> =0A>> Suggested-by: Thomas =
Gleixner <tglx@linutronix.de>=0A>> Suggested-by: Sean Christopherson <sean.=
j.christopherson@intel.com>=0A>> Suggested-by: Andy Lutomirski <luto@kernel=
.org>=0A>> Signed-off-by: David P. Reed <dpreed@deepplum.com>=0A>> ---=0A>>=
  arch/x86/include/asm/virtext.h | 20 ++++++++++++++------=0A>>  1 file cha=
nged, 14 insertions(+), 6 deletions(-)=0A>>=0A>> diff --git a/arch/x86/incl=
ude/asm/virtext.h b/arch/x86/include/asm/virtext.h=0A>> index 0ede8d04535a.=
.0e0900eacb9c 100644=0A>> --- a/arch/x86/include/asm/virtext.h=0A>> +++ b/a=
rch/x86/include/asm/virtext.h=0A>> @@ -30,11 +30,11 @@ static inline int cp=
u_has_vmx(void)=0A>>  }=0A>>=0A>>=0A>> -/* Disable VMX on the current CPU=
=0A>> +/* Exit VMX root mode and isable VMX on the current CPU.=0A> =0A> s/=
isable/disable/=0A> =0A> =0A>>  /* Disable VMX if it is supported and enabl=
ed on the current CPU=0A>> --=0A>> 2.26.2=0A>>=0A> =0A> Other than that:=0A=
> =0A> Reviewed-by: Andy Lutomirski <luto@kernel.org>=0A=0AAs a newbie, I h=
ave a process question - should I resend the patch with the 'Reviewed-by' l=
ine, as well as correcting the other wording? Thanks!=0A=0A> =0A> --Andy=0A=
> =0A