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From: Andy Lutomirski <luto@amacapital.net>
Date: Mon, 4 Apr 2016 09:40:51 -0700
Message-ID: <CALCETrUT8SCD=XLFXEPaNPtPddKzv+YO23GyAkLhgY+3fEJFAA@mail.gmail.com>
Subject: Re: [Xen-devel] [PATCH v5 7/9] x86/paravirt: Add paravirt_{read, write}_msr
To: David Vrabel <david.vrabel@citrix.com>
Cc: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        KVM list <kvm@vger.kernel.org>, Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        "linux-kernel@vger.kernel.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>
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On Mon, Apr 4, 2016 at 9:33 AM, David Vrabel <david.vrabel@citrix.com> wrote:
> 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.
>

It might be nice to do a WARN_ON_ONCE like this series does for the
native case to help shake out latent bugs.

--Andy