linux-kernel - Re: [Xen-devel] [PATCH v5 7/9] x86/paravirt: Add paravirt_{read, write}

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Date:	Mon, 4 Apr 2016 17:33:14 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>
CC:	KVM list <kvm@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>,
	xen-devel <Xen-devel@...ts.xen.org>,
	"Borislav Petkov" <bp@...en8.de>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [Xen-devel] [PATCH v5 7/9] x86/paravirt: Add paravirt_{read,
 write}_msr

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@...rix.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