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

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Date:	Mon, 13 Apr 2015 13:55:35 +0200
From:	Christoffer Dall <christoffer.dall@...aro.org>
To:	Alex Bennée <alex.bennee@...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

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.

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.


> + */
> +#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
> 
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