linux-kernel - Re: [RFC 02/10] x86/kvm: Add IBPB support

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Date:   Sat, 20 Jan 2018 20:18:05 +0000
From:   "Woodhouse, David" <dwmw@...zon.co.uk>
To:     KarimAllah Ahmed <karahmed@...zon.de>,
        <linux-kernel@...r.kernel.org>
CC:     Andi Kleen <ak@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        "Dave Hansen" <dave.hansen@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Laura Abbott <labbott@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Tom Lendacky <thomas.lendacky@....com>, <kvm@...r.kernel.org>,
        <x86@...nel.org>, "Arjan Van De Ven" <arjan.van.de.ven@...el.com>
Subject: Re: [RFC 02/10] x86/kvm: Add IBPB support

On Sat, 2018-01-20 at 20:22 +0100, KarimAllah Ahmed wrote:
> 
> @@ -6791,6 +6792,9 @@ static __init int hardware_setup(void)
>                 kvm_tsc_scaling_ratio_frac_bits = 48;
>         }
>  
> +       if (boot_cpu_has(X86_FEATURE_SPEC_CTRL))
> +               vmx_disable_intercept_for_msr(MSR_IA32_PRED_CMD, false);
> +

I've updated that to allow X86_FEATURE_AMD_PRED_CMD too, since some
hypervisors may expose *only* that MSR to guests even on Intel
hardware. PRED_CMD is a lot easier to expose as it doesn't need
storage, live migration support, and all that crap.

Our shared tree at
http://git.infradead.org/linux-retpoline.git/shortlog/refs/heads/ibpb
updated accordingly.


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