linux-kernel - Re: [PATCH v2 02/10] KVM: define common __KVM_GUESTDBG_USE_SW/HW

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Date:	Mon, 13 Apr 2015 15:51:33 +0100
From:	Alex Bennée <alex.bennee@...aro.org>
To:	Christoffer Dall <christoffer.dall@...aro.org>
Cc:	kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.cs.columbia.edu, marc.zyngier@....com,
	peter.maydell@...aro.org, agraf@...e.de, drjones@...hat.com,
	pbonzini@...hat.com, zhichao.huang@...aro.org,
	jan.kiszka@...mens.com, dahi@...ux.vnet.ibm.com,
	r65777@...escale.com, bp@...e.de,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"maintainer\:X86 ARCHITECTURE..." <x86@...nel.org>,
	Gleb Natapov <gleb@...nel.org>,
	Bharat Bhushan <Bharat.Bhushan@...escale.com>,
	Alexey Kardashevskiy <aik@...abs.ru>,
	Mihai Caraman <mihai.caraman@...escale.com>,
	Nadav Amit <namit@...technion.ac.il>,
	"open list\:LINUX FOR POWERPC..." <linuxppc-dev@...ts.ozlabs.org>,
	open list <linux-kernel@...r.kernel.org>,
	"open list\:ABI\/API" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2 02/10] KVM: define common __KVM_GUESTDBG_USE_SW/HW_BP values


Christoffer Dall <christoffer.dall@...aro.org> writes:

> On Tue, Mar 31, 2015 at 04:08:00PM +0100, Alex Bennée wrote:
>> Currently x86, powerpc and soon arm64 use the same two architecture
>> specific bits for guest debug support for software and hardware
>> breakpoints. This makes the shared values explicit while leaving the
>> gate open for another architecture to use some other value if they
>> really really want to.
>> 
>> Signed-off-by: Alex Bennée <alex.bennee@...aro.org>
>> 
>> diff --git a/arch/powerpc/include/uapi/asm/kvm.h b/arch/powerpc/include/uapi/asm/kvm.h
>> index ab4d473..1731569 100644
>> --- a/arch/powerpc/include/uapi/asm/kvm.h
>> +++ b/arch/powerpc/include/uapi/asm/kvm.h
>> @@ -310,8 +310,8 @@ struct kvm_guest_debug_arch {
>>   * and upper 16 bits are architecture specific. Architecture specific defines
>>   * that ioctl is for setting hardware breakpoint or software breakpoint.
>>   */
>> -#define KVM_GUESTDBG_USE_SW_BP		0x00010000
>> -#define KVM_GUESTDBG_USE_HW_BP		0x00020000
>> +#define KVM_GUESTDBG_USE_SW_BP		__KVM_GUESTDBG_USE_SW_BP
>> +#define KVM_GUESTDBG_USE_HW_BP		__KVM_GUESTDBG_USE_HW_BP
>>  
>>  /* definition of registers in kvm_run */
>>  struct kvm_sync_regs {
>> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
>> index d7dcef5..1438202 100644
>> --- a/arch/x86/include/uapi/asm/kvm.h
>> +++ b/arch/x86/include/uapi/asm/kvm.h
>> @@ -250,8 +250,8 @@ struct kvm_debug_exit_arch {
>>  	__u64 dr7;
>>  };
>>  
>> -#define KVM_GUESTDBG_USE_SW_BP		0x00010000
>> -#define KVM_GUESTDBG_USE_HW_BP		0x00020000
>> +#define KVM_GUESTDBG_USE_SW_BP		__KVM_GUESTDBG_USE_SW_BP
>> +#define KVM_GUESTDBG_USE_HW_BP		__KVM_GUESTDBG_USE_HW_BP
>>  #define KVM_GUESTDBG_INJECT_DB		0x00040000
>>  #define KVM_GUESTDBG_INJECT_BP		0x00080000
>>  
>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index 5eedf84..ce2db14 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -525,8 +525,16 @@ struct kvm_s390_irq {
>>  
>>  /* for KVM_SET_GUEST_DEBUG */
>>  
>> -#define KVM_GUESTDBG_ENABLE		0x00000001
>> -#define KVM_GUESTDBG_SINGLESTEP		0x00000002
>> +#define KVM_GUESTDBG_ENABLE		(1 << 0)
>> +#define KVM_GUESTDBG_SINGLESTEP	(1 << 1)
>> +
>> +/*
>> + * Architecture specific stuff uses the top 16 bits of the field,
>
> can you be more specific than 'stuff' here?  features?
>
>> + * however there is some shared commonality for the common cases
>
> I don't like this sentence; shared commonality is a pleonasm and the use
> of however makes it sounds like there's some caveat here.

OK I can see that - after I looked it up ;-)

> If the top 16 bits are indeed arhictecture specific, then I think they
> should just be defined in their architecture specific headers.  Unless
> the idea here is that there's a fixed set of of flags that architectures
> can choose to support, in which case it should simply be defined in the
> common header.

Well an architecture might not support some features and want to use
those bits for something else? I didn't want to force the bottom two
of the architecture specific bits to wasted if the features don't exist.

>
>
>> + */
>> +#define __KVM_GUESTDBG_USE_SW_BP	(1 << 16)
>> +#define __KVM_GUESTDBG_USE_HW_BP	(1 << 17)
>> +
>>  
>>  struct kvm_guest_debug {
>>  	__u32 control;
>> -- 
>> 2.3.4
>> 

-- 
Alex Bennée
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