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Subject: Re: [Xen-devel] [PATCH v5 7/9] x86/paravirt: Add paravirt_{read,
 write}_msr
To: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>
References: <cover.1459605520.git.luto@kernel.org>
 <880eebc5dcd2ad9f310d41345f82061ea500e9fa.1459605520.git.luto@kernel.org>
CC: KVM list <kvm@vger.kernel.org>, Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        <linux-kernel@vger.kernel.org>, xen-devel <Xen-devel@lists.xen.org>,
        "Borislav Petkov" <bp@alien8.de>, Paolo Bonzini <pbonzini@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Arjan van de Ven <arjan@linux.intel.com>
From: David Vrabel <david.vrabel@citrix.com>
Message-ID: <5702974A.1030003@citrix.com>
Date: Mon, 4 Apr 2016 17:33:14 +0100
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On 02/04/16 15:01, Andy Lutomirski wrote:
> This adds paravirt hooks for unsafe MSR access.  On native, they
> call native_{read,write}_msr.  On Xen, they use
> xen_{read,write}_msr_safe.
> 
> Nothing uses them yet for ease of bisection.  The next patch will
> use them in rdmsrl, wrmsrl, etc.
> 
> I intentionally didn't make them warn on #GP on Xen.  I think that
> should be done separately by the Xen maintainers.
...
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c

Reviewed-by: David Vrabel <david.vrabel@citrix.com>

> @@ -1092,6 +1092,26 @@ static int xen_write_msr_safe(unsigned int msr, unsigned low, unsigned high)
>  	return ret;
>  }
>  
> +static u64 xen_read_msr(unsigned int msr)
> +{
> +	/*
> +	 * This will silently swallow a #GP from RDMSR.  It may be worth
> +	 * changing that.

This probably isn't important.

David