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Subject: Re: [PATCH] x86/entry/64: Disallow RDPID in paranoid entry if KVM is
 enabled
To:     Borislav Petkov <bp@alien8.de>
Cc:     Sean Christopherson <sean.j.christopherson@intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, linux-kernel@vger.kernel.org,
        Dave Hansen <dave.hansen@intel.com>,
        Chang Seok Bae <chang.seok.bae@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Sasha Levin <sashal@kernel.org>, kvm@vger.kernel.org,
        Tom Lendacky <thomas.lendacky@amd.com>
References: <20200821025050.32573-1-sean.j.christopherson@intel.com>
 <20200821074743.GB12181@zn.tnic>
 <3eb94913-662d-5423-21b1-eaf75635142a@redhat.com>
 <20200821081633.GD12181@zn.tnic>
 <3b4ba9e9-dbf6-a094-0684-e68248050758@redhat.com>
 <20200821092237.GF12181@zn.tnic>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <1442e559-dde4-70f6-85ac-58109cf81c16@redhat.com>
Date:   Fri, 21 Aug 2020 11:44:33 +0200
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On 21/08/20 11:22, Borislav Petkov wrote:
>> Hence the assumption that KVM makes (and has made ever since TSC_AUX was
>> introduced.
> And *this* is the problem. KVM can't just be grabbing MSRs and claiming
> them because it started using them first. You guys need to stop this. If
> it is a shared resource, there better be an agreement about sharing it.

It's not like we grab MSRs every day.  The user-return notifier restores
6 MSRs (7 on very old processors).  The last two that were added were
MSR_TSC_AUX itself in 2009 (!) and MSR_IA32_TSX_CTRL last year.

Paolo