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

[Don Slutz <dslutz@verizon.com>]

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
>