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Date:   Fri, 21 Aug 2020 10:16:33 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Paolo Bonzini <pbonzini@redhat.com>
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>
Subject: Re: [PATCH] x86/entry/64: Disallow RDPID in paranoid entry if KVM is
 enabled
Message-ID: <20200821081633.GD12181@zn.tnic>
References: <20200821025050.32573-1-sean.j.christopherson@intel.com>
 <20200821074743.GB12181@zn.tnic>
 <3eb94913-662d-5423-21b1-eaf75635142a@redhat.com>
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On Fri, Aug 21, 2020 at 10:09:01AM +0200, Paolo Bonzini wrote:
> One more MSR *is* a big deal: KVM's vmentry+vmexit cost is around 1000
> cycles, adding 100 clock cycles for 2 WRMSRs is a 10% increase.

The kernel uses TSC_AUX so we can't reserve it to KVM either.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette