linux-kernel - Re: [PATCH 3/8] kvm: vmx: pass MSR_IA32_SPEC_CTRL and MSR_IA32_PRED

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Message-ID: <alpine.DEB.2.20.1801151033140.1810@nanos>
Date:   Mon, 15 Jan 2018 10:34:59 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Paolo Bonzini <pbonzini@...hat.com>
cc:     "Longpeng (Mike)" <longpeng2@...wei.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        rkrcmar@...hat.com, liran.alon@...cle.com, jmattson@...gle.com,
        aliguori@...zon.com, thomas.lendacky@....com, dwmw@...zon.co.uk,
        bp@...en8.de, x86@...nel.org, Gonglei <arei.gonglei@...wei.com>
Subject: Re: [PATCH 3/8] kvm: vmx: pass MSR_IA32_SPEC_CTRL and MSR_IA32_PRED_CMD
 down to the guest

On Mon, 15 Jan 2018, Paolo Bonzini wrote:

> On 13/01/2018 11:16, Longpeng (Mike) wrote:
> >> +	/*
> >> +	 * FIXME: this is only needed until SPEC_CTRL is supported
> >> +	 * by upstream Linux in cpufeatures, then it can be replaced
> >> +	 * with static_cpu_has.
> >> +	 */
> >> +	have_spec_ctrl = cpu_has_spec_ctrl();
> >> +	if (have_spec_ctrl)
> >> +		pr_info("kvm: SPEC_CTRL available\n");
> >> +	else
> >> +		pr_info("kvm: SPEC_CTRL not available\n");
> >> +
> > 
> > In this approach, we must reload these modules if we update the microcode later ?
> 
> I strongly suggest using early microcode update anyway.

We had the discussion already and we are not going to support late micro
code loading. It's just not worth the trouble.

Also please do not commit any of this before we have sorted out the bare
metal IBRS/IBPB support. We really don't want to have two variants of that
in tree.

Thanks,

	tglx