Re: [Xen-devel] [PATCH 01/13] Nested Virtualization: tools

[George Dunlap <dunlapg@xxxxxxxxx>]

On Tue, Nov 16, 2010 at 11:52 AM, Christoph Egger
<Christoph.Egger@xxxxxxx> wrote:
> On Tuesday 16 November 2010 12:37:06 Tim Deegan wrote:
>> Hi,
>>
>> At 18:40 +0000 on 12 Nov (1289587225), Christoph Egger wrote:
>> > +#define SVM_FEATURE_NPT            0x00000001
>> > +#define SVM_FEATURE_LBRV           0x00000002
>> > +#define SVM_FEATURE_SVML           0x00000004
>> > +#define SVM_FEATURE_NRIPS          0x00000008
>> > +#define SVM_FEATURE_PAUSEFILTER    0x00000400
>> > +
>> > +        /* Only passthrough SVM features which are implemented */
>> > +        edx = 0;
>> > +        if (regs[3] & SVM_FEATURE_NPT)
>> > +            edx |= SVM_FEATURE_NPT;
>> > +        if (regs[3] & SVM_FEATURE_LBRV)
>> > +            edx |= SVM_FEATURE_LBRV;
>> > +        if (regs[3] & SVM_FEATURE_NRIPS)
>> > +            edx |= SVM_FEATURE_NRIPS;
>> > +        if (regs[3] & SVM_FEATURE_PAUSEFILTER)
>> > +            edx |= SVM_FEATURE_PAUSEFILTER;
>> > +
>> > +        regs[3] = edx;
>>
>> Minor niggle - why isn't this just a single &= operation?
>
> The l1 guest shouldn't see upcoming svm features yet.
> They will be added here when support for them is implemented.

I think Tim is suggesting this:
 regs[3] &= SVM_FEATURE_NPT|SVM_FEATURE_LBRV|...

Which will have the same effect.
 -George

>
> Christoph
>
>
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