From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alex =?utf-8?Q?Benn=C3=A9e?= <alex.bennee@linaro.org>
Subject: Re: Exposing host debug capabilities to userspace
Date: Mon, 24 Nov 2014 13:59:51 +0000
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To: Will Deacon <will.deacon@arm.com>,
	Marc Zyngier <marc.zyngier@arm.com>,
	Christoffer Dall <christoffer.dall@linaro.org>,
	Peter Maydell <peter.maydell@linaro.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Alexander Graf <agraf@suse.de>
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Alex Benn=C3=A9e <alex.bennee@linaro.org> writes:

<snip>
> Alex Benn=C3=A9e <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 deb=
ug
>> registers are available for GDB to use. This information is availabl=
e
>> from the ID_AA64DFR0_EL1 register.
<Snip>
>> So far the options I've examined are:
>>
>> * KVM ioctl GET_ONE_REG(ID_AA64DFR0_EL1)
>> * ptrace(PTRACE_GETREGSET, NT_ARM_HW_WATCH)
>> * KVM ioctl KVM_GET_DEBUGREGS
>> * Export the information via sysfs
>> * Expand /proc/cpuinfo
>> * Add another KVM ioctl?

Alexander Graf pointed out that KVM_CHECK_EXTENSION can return any
positive number for success. How about using:

max_hw_bps =3D kvm_check_extension(kvm_state, KVM_CAP_GUEST_DEBUG_HW_BP=
S);
max_hw_wps =3D kvm_check_extension(kvm_state, KVM_CAP_GUEST_DEBUG_HW_WP=
S);

Seems pretty sane, doesn't change the semantics of an API and is
architecture agnostic if others need the number?

--=20
Alex Benn=C3=A9e