Re: [PATCH v1 2/3] kvm: svm: Add kvm_fast_pio_in support

[Tom Lendacky]

On 11/21/2016 8:50 AM, Paolo Bonzini wrote:
> 
> 
> On 14/11/2016 23:15, Brijesh Singh wrote:
>> +	/* For size less than 4 we merge, else we zero extend */
>> +	val = (size < 4) ? kvm_register_read(vcpu, VCPU_REGS_RAX) : 0;
> 
> Are you sure it shouldn't always zero extend the high 32-bits?  So "val"
> should be declared as u32.
> 
> Paolo

It should only zero extend when dealing with a 32-bit operation. Any use
of 8 or 16 bit registers leaves the upper 56 or 48 bits as is (see
section 3.1.2.3 in http://support.amd.com/TechDocs/24592.pdf).

Thanks,
Tom

> 
>> +	ret = emulator_pio_in_emulated(&vcpu->arch.emulate_ctxt, size, port,
>> +				       &val, 1);
>> +	if (ret) {
>> +		kvm_register_write(vcpu, VCPU_REGS_RAX, val);
>> +		return ret;
>> +	}