Re: [Xen-devel] [PATCH for-4.5 v6 04/16] xen: Add vmware_port support

[Don Slutz <dslutz@xxxxxxxxxxx>]

On 09/23/14 13:16, Boris Ostrovsky wrote:
> On 09/20/2014 02:07 PM, Don Slutz wrote:
> > @@ -2064,6 +2065,42 @@ svm_vmexit_do_vmsave(struct vmcb_struct *vmcb,
> >       return;
> >   }
> >   +static void svm_vmexit_gp_intercept(struct cpu_user_regs *regs,
> > +                                    struct vcpu *v)
> > +{
> > +    struct vmcb_struct *vmcb = v->arch.hvm_svm.vmcb;
> > +    /*
> > +     * Just use 15 for the instruction length; vmport_gp_check will
> > +     * adjust it.  This is because
> > +     * __get_instruction_length_from_list() has issues, and may
> > +     * require a double read of the instruction bytes.  At some
> > +     * point a new routine could be added that is based on the code
> > +     * in vmport_gp_check with extensions to make it more general.
> > +     * Since that routine is the only user of this code this can be
> > +     * done later.
> > +     */
> > +    unsigned long inst_len = 15;
> Can you add a comment describing why you chose 15?
>
> Also, saying that __get_instruction_length_from_list() has issues I 
> think requires a bit more details (e.g. that when called from #GP 
> handler NRIP is not available, or that NRIP may not be available at 
> all on a particular HW, leading to the need read the instruction twice 
> --- once in __get_instruction_length_from_list() and then again in 
> vmport_gp_check(). Which is bad because memory may change between the 
> reads. Or something like that.).
Added more on the commit message about this.

   -Don Slutz

> -boris

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