From: Thomas Gleixner <tglx@linutronix.de>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: "David P. Reed" <dpreed@deepplum.com>,
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: Thu, 11 Jun 2020 00:08:48 +0200 [thread overview]
Message-ID: <87wo4evaj3.fsf@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20200610214231.GH18790@linux.intel.com>
Sean Christopherson <sean.j.christopherson@intel.com> writes:
> Gah, I typed too slow :-)
Haha. I had the same thought.
> On Wed, Jun 10, 2020 at 11:34:21PM +0200, Thomas Gleixner wrote:
>> We have exception fixups to avoid exactly that kind of horrible
>> workarounds all over the place.
>>
>> static inline int cpu_vmxoff_safe(void)
>> {
>> int err;
>>
>> asm volatile("2: vmxoff; xor %[err],%[err]\n"
>> "1:\n\t"
>> ".section .fixup,\"ax\"\n\t"
>> "3: mov %[fault],%[err] ; jmp 1b\n\t"
>> ".previous\n\t"
>> _ASM_EXTABLE(2b, 3b)
>> : [err] "=a" (err)
>> : [fault] "i" (-EFAULT)
>> : "memory");
>> return err;
>> }
>>
>> static inline void __cpu_emergency_vmxoff(void)
>> {
>> if (!cpu_vmx_enabled())
>> return;
>> if (!cpu_vmxoff_safe())
>> cr4_clear_bits(X86_CR4_VMXE);
>
> This bit is wrong, CR4.VMXE should be cleared even if VMXOFF faults, e.g.
> if this is called in NMI context and the NMI arrived in KVM code between
> VMXOFF and clearing CR4.VMXE.
Oh, right.
> All other VMXOFF faults are mode related, i.e. any fault is guaranteed to
> be due to the !post-VMXON check unless we're magically in RM, VM86, compat
> mode, or at CPL>0.
Your patch is simpler indeed.
Thanks,
tglx
next prev parent reply other threads:[~2020-06-10 22:09 UTC|newest]
Thread overview: 14+ 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 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 [this message]
2020-06-10 21:36 ` Sean Christopherson
2020-06-10 21:59 ` Andy Lutomirski
2020-06-11 0:00 ` Sean Christopherson
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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