Re: [PATCH v2 0/9] arm64: KVM: debug infrastructure support

Marc Zyngier
2014-05-28T09:56:55Z

On 25/05/14 16:34, Christoffer Dall wrote:
> On Tue, May 20, 2014 at 05:55:36PM +0100, Marc Zyngier wrote:
>> This patch series adds debug support, a key feature missing from the
>> KVM/arm64 port.
>>
>> The main idea is to keep track of whether the debug registers are
>> "dirty" (changed by the guest) or not. In this case, perform the usual
>> save/restore dance, for one run only. It means we only have a penalty
>> if a guest is actively using the debug registers.
>>
>> The amount of registers is properly frightening, but CPUs actually
>> only implement a subset of them. Also, there is a number of registers
>> we don't bother emulating (things having to do with external debug and
>> OSlock).
>
> What is the rationale about not having to deal with external debug and
> OSlock?

External debug is when you actually plug a physical JTAG into the CPU.
OSlock is a way to prevent "other software" to play with the debug
registers. My understanding is that it is only useful in combination
with the external debug.

In both case, implementing support for this is probably not worth the
effort, at least for the time being.

M.
--
Jazz is not dead. It just smells funny...