linux-kernel - Re: [PATCH v2 03/10] KVM: arm: guest debug, define API headers

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Date:	Mon, 13 Apr 2015 14:08:13 +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,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 03/10] KVM: arm: guest debug, define API headers

On Tue, Mar 31, 2015 at 04:08:01PM +0100, Alex Bennée wrote:
> This commit defines the API headers for guest debugging. There are two
> architecture specific debug structures:
> 
>   - kvm_guest_debug_arch, allows us to pass in HW debug registers
>   - kvm_debug_exit_arch, signals the exact debug exit and pc
> 
> The type of debugging being used is control by the architecture specific
> control bits of the kvm_guest_debug->control flags in the ioctl
> structure.
> 
> Signed-off-by: Alex Bennée <alex.bennee@...aro.org>
> 
> ---
> v2
>    - expose hsr and pc directly to user-space
> 
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index 3ef77a4..6ee70a0 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -100,10 +100,24 @@ struct kvm_sregs {
>  struct kvm_fpu {
>  };
>  
> +/*
> + * See ARM ARM D7.3: Debug Registers

see the ARM ARM for ??

> + *
> + * The control registers are architecturally defined as 32 bits but are
> + * stored as 64 bit values along side the value registers and aligned

do you mean alongside?

> + * with the rest 64 bit registers in the normal CPU context.

rest of the 64 bit

> + */

why do we store them as 64 bit values?  There's nothing prevented us
from defining them as __u32 is there?  Is this to make the ONE_REG
interface accessers more convenient?

> +#define KVM_ARM_NDBG_REGS 16

nit: is NDBG short for something I don't know about or is it
the number of debug registers we are noting here, in which case I think
KVM_ARM_NUM_DBG_REGS is more clear.

>  struct kvm_guest_debug_arch {
> +	__u64 dbg_bcr[KVM_ARM_NDBG_REGS];
> +	__u64 dbg_bvr[KVM_ARM_NDBG_REGS];
> +	__u64 dbg_wcr[KVM_ARM_NDBG_REGS];
> +	__u64 dbg_wvr[KVM_ARM_NDBG_REGS];
>  };
>  
>  struct kvm_debug_exit_arch {
> +	__u64 pc;
> +	__u32 hsr;
>  };
>  
>  struct kvm_sync_regs {
> @@ -207,4 +221,11 @@ struct kvm_arch_memory_slot {
>  
>  #endif
>  
> +/*
> + * Architecture related debug defines - upper 16 bits of
> + * kvm_guest_debug->control
> + */
> +#define KVM_GUESTDBG_USE_SW_BP	        __KVM_GUESTDBG_USE_SW_BP
> +#define KVM_GUESTDBG_USE_HW_BP		__KVM_GUESTDBG_USE_HW_BP
> +
>  #endif /* __ARM_KVM_H__ */
> -- 
> 2.3.4
> 

Thanks,
-Christoffer
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