Re: Exposing host debug capabilities to userspace

[Alexander Graf <agraf@suse.de>]

On 24.11.14 12:35, Alex Bennée wrote:
> 
> Fixed CC:kvmarm, Added: Alexander Graf, Fixed: my From:
> 
> Replying to myself with additional information on each option
> 
> Alex Bennée <alex.bennee@linaro.org> writes:
> 
>> Hi,
>>
>> I've almost finished the ARMv8 guest debug support but I have one
>> problem left to solve. userspace needs to know how many hardware debug
>> registers are available for GDB to use. This information is available
>> from the ID_AA64DFR0_EL1 register. Currently I abuse GET_ONE_REG to
>> fetch it's value however semantically this is poor as it's API is for
>> getting guest state not host state and they could theoretically have
>> different values.
>>
>> So far the options I've examined are:
>>
>> * KVM ioctl GET_ONE_REG(ID_AA64DFR0_EL1)
> Nope, guest state API

What's the problem with using ONE_REG for this? After all, the total
number of available guest debug register is a guest vcpu property of
some sort.

Btw, looking through the mess that we have today with asymmetric
SET_GUEST_DEBUG and GET_DEBUGREGS ioctls I can't shake off the feeling
that we're best off just doing all of the debug register sync via
ONE_REGs. That way we at least have a guaranteed symmetric interface
that can get and set values, so we won't trip over it on live migration.


Alex