From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alexander Graf <agraf@suse.de>
Subject: Re: Exposing host debug capabilities to userspace
Date: Mon, 24 Nov 2014 13:26:19 +0100
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On 24.11.14 12:35, Alex Benn=C3=A9e wrote:
>=20
> Fixed CC:kvmarm, Added: Alexander Graf, Fixed: my From:
>=20
> Replying to myself with additional information on each option
>=20
> Alex Benn=C3=A9e <alex.bennee@linaro.org> writes:
>=20
>> 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 deb=
ug
>> registers are available for GDB to use. This information is availabl=
e
>> 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 fo=
r
>> 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=
=2E


Alex