linux-kernel - Re: [PATCH] x86/entry/64: Disallow RDPID in paranoid entry if KVM is enabled

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Message-ID: <20200821200207.GW3982@worktop.programming.kicks-ass.net>
Date:   Fri, 21 Aug 2020 22:02:07 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     hpa@...or.com
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Chang Seok Bae <chang.seok.bae@...el.com>,
        Sasha Levin <sashal@...nel.org>, kvm@...r.kernel.org,
        Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH] x86/entry/64: Disallow RDPID in paranoid entry if KVM is
 enabled

On Fri, Aug 21, 2020 at 12:55:53PM -0700, hpa@...or.com wrote:

> It is hardly going to be a performance difference for paranoid entry,
> which is hopefully rare enough that it falls into the noise.

Try perf some day ;-)

But yeah, given the utter trainwreck that NMIs are anyway, this is all
not going to matter much.