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Message-ID: <87imitev67.fsf@nanos.tec.linutronix.de>
Date: Tue, 24 Mar 2020 14:31:28 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Xiaoyao Li <xiaoyao.li@...el.com>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, hpa@...or.com,
Paolo Bonzini <pbonzini@...hat.com>,
Sean Christopherson <sean.j.christopherson@...el.com>,
kvm@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org
Cc: Andy Lutomirski <luto@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Arvind Sankar <nivedita@...m.mit.edu>,
Fenghua Yu <fenghua.yu@...el.com>,
Tony Luck <tony.luck@...el.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v5 1/9] x86/split_lock: Rework the initialization flow of split lock detection
Xiaoyao Li <xiaoyao.li@...el.com> writes:
> On 3/24/2020 1:02 AM, Thomas Gleixner wrote:
>> Xiaoyao Li <xiaoyao.li@...el.com> writes:
>>
>>> Current initialization flow of split lock detection has following issues:
>>> 1. It assumes the initial value of MSR_TEST_CTRL.SPLIT_LOCK_DETECT to be
>>> zero. However, it's possible that BIOS/firmware has set it.
>>
>> Ok.
>>
>>> 2. X86_FEATURE_SPLIT_LOCK_DETECT flag is unconditionally set even if
>>> there is a virtualization flaw that FMS indicates the existence while
>>> it's actually not supported.
>>>
>>> 3. Because of #2, KVM cannot rely on X86_FEATURE_SPLIT_LOCK_DETECT flag
>>> to check verify if feature does exist, so cannot expose it to
>>> guest.
>>
>> Sorry this does not make anny sense. KVM is the hypervisor, so it better
>> can rely on the detect flag. Unless you talk about nested virt and a
>> broken L1 hypervisor.
>>
>
> Yeah. It is for the nested virt on a broken L1 hypervisor.
Then please spell it out in the changelog. Changelogs which need crystalballs
to decode are pretty useless.
Thanks,
tglx
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