linux-kernel - Re: [PATCH 2/7] KVM: arm: guest debug, define API headers

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Date:	Wed, 26 Nov 2014 17:46:05 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Alex Bennée <alex.bennee@...aro.org>,
	Andrew Jones <drjones@...hat.com>
CC:	kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.cs.columbia.edu, christoffer.dall@...aro.org,
	marc.zyngier@....com, peter.maydell@...aro.org, agraf@...e.de,
	Catalin Marinas <catalin.marinas@....com>,
	jan.kiszka@...mens.com, Will Deacon <will.deacon@....com>,
	open list <linux-kernel@...r.kernel.org>,
	dahi@...ux.vnet.ibm.com, r65777@...escale.com, bp@...e.de
Subject: Re: [PATCH 2/7] KVM: arm: guest debug, define API headers



On 26/11/2014 15:58, Alex Bennée wrote:
> 
> Andrew Jones <drjones@...hat.com> writes:
> 
>> On Tue, Nov 25, 2014 at 04:10:00PM +0000, Alex Bennée wrote:
>>> This commit defines the API headers for guest debugging. There are two
>>> architecture specific debug structures:
> <snip>
>>> +/* Architecture related debug defines - upper 16 bits of
>>> + * kvm_guest_debug->control
>>> + */
>>> +#define KVM_GUESTDBG_USE_SW_BP_SHIFT	16
>>> +#define KVM_GUESTDBG_USE_SW_BP		(1 << KVM_GUESTDBG_USE_SW_BP_SHIFT)
>>> +#define KVM_GUESTDBG_USE_HW_BP_SHIFT	17
>>> +#define KVM_GUESTDBG_USE_HW_BP		(1 << KVM_GUESTDBG_USE_HW_BP_SHIFT)
>>> +
>>
>> I see this are defined in arch/x86/include/uapi/asm/kvm.h,
>> so you needed to reproduce them here, but shouldn't they
>> be promoted to include/uapi/linux/kvm.h instead?
> 
> Well if we move them to common uapi we either restrict the $ARCH
> specific options that don't have SW/HW BKPTS (would be weird but...) or
> make them generic in the lower 16 bits (breaks API).
> 
> But in principle I have no objection if other don't.

I think it's a matter of personal taste.  "Architecture-specific" means
"not all architectures may support it", but it's certainly a good idea
to reuse the same value if multiple architectures do support a #define.

What you did is fine, another possibility is to do

    #define __KVM_GUESTDBG_USE_SW_BP   (1 << 16)

in include/uapi/linux/kvm.h, and

    #define KVM_GUESTDBG_USE_SW_BP __KVM_GUESTDBG_USE_SW_BP

in the arch-specific file.  Andrew, is this closer to what you intended?

Paolo
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