From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: "David P. Reed" <dpreed@deepplum.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
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>,
"Peter Zijlstra (Intel)" <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>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Fix undefined operation VMXOFF during reboot and crash
Date: Wed, 10 Jun 2020 17:00:32 -0700 [thread overview]
Message-ID: <20200611000032.GI18790@linux.intel.com> (raw)
In-Reply-To: <3F5CEF02-0561-4E28-851B-8E993F76DC9B@amacapital.net>
On Wed, Jun 10, 2020 at 02:59:19PM -0700, Andy Lutomirski wrote:
>
>
> > On Jun 10, 2020, at 11:21 AM, David P. Reed <dpreed@deepplum.com> wrote:
> >
> > If a panic/reboot occurs when CR4 has VMX enabled, a VMXOFF is
> > done on all CPUS, to allow the INIT IPI to function, since
> > INIT is suppressed when CPUs are in VMX root operation.
> > However, VMXOFF causes an undefined operation fault if the CPU is not
> > in VMX operation, that is, VMXON has not been executed, or VMXOFF
> > has been executed, but VMX is enabled.
>
> I’m surprised. Wouldn’t this mean that emergency reboots always fail it a VM
> is running? I would think someone would have noticed before.
The call to cpu_vmxoff() is conditioned on CR4.VMXE==1, which KVM toggles in
tandem with VMXON and VMXOFF. Out of tree hypervisors presumably do the
same. That's obviously not atomic though, e.g. VMXOFF will #UD if the
vmxoff_nmi() NMI arrives between CR4.VMXE=1 and VMXON, or between VMXOFF
and CR4.VMXE=0.
next prev parent reply other threads:[~2020-06-11 0:00 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-10 18:12 [PATCH] Fix undefined operation VMXOFF during reboot and crash David P. Reed
2020-06-10 18:58 ` kernel test robot
2020-06-10 19:36 ` Randy Dunlap
2020-06-10 21:34 ` Thomas Gleixner
2020-06-10 21:42 ` Sean Christopherson
2020-06-10 22:08 ` Thomas Gleixner
2020-06-10 21:36 ` Sean Christopherson
2020-06-10 21:59 ` Andy Lutomirski
2020-06-11 0:00 ` Sean Christopherson [this message]
2020-06-11 0:15 ` Andy Lutomirski
[not found] ` <1591893200.58634165@apps.rackspace.com>
2020-06-11 17:00 ` Sean Christopherson
2020-06-11 17:02 ` Andy Lutomirski
2020-06-11 19:45 ` [PATCH v2] " David P. Reed
2020-06-11 19:48 ` David P. Reed
2020-06-25 6:06 ` Sean Christopherson
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