linux-kernel - Re: [Xen-devel] [PATCH v2 2/3] x86 Test and expose CPUID faulting capabilities in /proc/cpuinfo

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Message-ID: <57DA724E.6090606@citrix.com>
Date:   Thu, 15 Sep 2016 11:05:02 +0100
From:   David Vrabel <david.vrabel@...rix.com>
To:     Kyle Huey <me@...ehuey.com>,
        Robert O'Callahan <robert@...llahan.org>
CC:     Juergen Gross <jgross@...e.com>, Len Brown <len.brown@...el.com>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Kristen Carlson Accardi <kristen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "maintainer:X86 ARCHITECTURE 32-BIT AND 64-BIT" <x86@...nel.org>,
        Huang Rui <ray.huang@....com>,
        "open list:X86 ARCHITECTURE 32-BIT AND 64-BIT" 
        <linux-kernel@...r.kernel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        "Aravind Gopalakrishnan" <aravind.gopalakrishnan@....com>,
        David Vrabel <david.vrabel@...rix.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        "moderated list:XEN HYPERVISOR INTERFACE" 
        <xen-devel@...ts.xenproject.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
Subject: Re: [Xen-devel] [PATCH v2 2/3] x86 Test and expose CPUID faulting
 capabilities in /proc/cpuinfo

On 14/09/16 22:01, Kyle Huey wrote:
> Xen advertises the underlying support for CPUID faulting but not does pass
> through writes to the relevant MSR, nor does it virtualize it, so it does
> not actually work. For now mask off the relevant bit on MSR_PLATFORM_INFO.

Could you clarify in the commit message that it is PV guests that are
affected.

> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -1050,6 +1050,9 @@ static u64 xen_read_msr_safe(unsigned int msr, int *err)
>  #endif
>  			val &= ~X2APIC_ENABLE;
>  		break;
> +	case MSR_PLATFORM_INFO:
> +		val &= ~CPUID_FAULTING_SUPPORT;
> +		break;
>  	}
>  	return val;
>  }

Acked-by: David Vrabel <david.vrabel@...rix.com>

David