linux-kernel - Re: [PATCH v3 21/23] arm64: hw_breakpoint: Allow EL2 breakpoints if running in HYP

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Message-ID: <20160208155625.GQ6076@e104818-lin.cambridge.arm.com>
Date:	Mon, 8 Feb 2016 15:56:26 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Marc Zyngier <marc.zyngier@....com>
Cc:	Will Deacon <will.deacon@....com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	kvmarm@...ts.cs.columbia.edu, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org
Subject: Re: [PATCH v3 21/23] arm64: hw_breakpoint: Allow EL2 breakpoints if
 running in HYP

On Wed, Feb 03, 2016 at 06:00:14PM +0000, Marc Zyngier wrote:
> @@ -76,6 +59,36 @@ static inline void decode_ctrl_reg(u32 reg,
>  #define ARM_KERNEL_STEP_ACTIVE	1
>  #define ARM_KERNEL_STEP_SUSPEND	2
>  
> +#define DBG_HMC_HYP		(1 << 13)
> +#define DBG_SSC_HYP		(3 << 14)
> +
> +static inline u32 encode_ctrl_reg(struct arch_hw_breakpoint_ctrl ctrl)
> +{
> +	u32 val = (ctrl.len << 5) | (ctrl.type << 3) | ctrl.enabled;
> +
> +	if (is_kernel_in_hyp_mode() && ctrl.privilege == AARCH64_BREAKPOINT_EL1)
> +		val |= DBG_HMC_HYP | DBG_SSC_HYP;
> +	else
> +		val |= ctrl.privilege << 1;
> +
> +	return val;
> +}
> +
> +static inline void decode_ctrl_reg(u32 reg,
> +				   struct arch_hw_breakpoint_ctrl *ctrl)
> +{
> +	ctrl->enabled	= reg & 0x1;
> +	reg >>= 1;
> +	if (is_kernel_in_hyp_mode())
> +		ctrl->privilege = !!(reg & (DBG_HMC_HYP >> 1));

I don't particularly like this part as it's not clear just by looking at
the code that it, in fact, generates AARCH64_BREAKPOINT_EL1. I would
make this clearer:

	if (is_kernel_in_hyp_mode() && (reg & (DBG_HMC_HYP >> 1)))
		ctrl->privilege = AARCH64_BREAKPOINT_EL1;

Alternatively, you could define the PMC field value as:

#define AARCH64_BREAKPOINT_EL2	0

and change the privilege to EL1 after masking, something like:

	ctrl->privilege = reg & 0x3;
	if (ctrl->privilege == AARCH64_BREAKPOINT_EL2)
		ctrl->privilege = AARCH64_BREAKPOINT_EL1;

BTW, do we need to check is_kernel_in_hyp_mode() when decoding? Is there
anything else that could have set this SSC/HMC/PMC fields other than
encode_ctrl_reg()?

-- 
Catalin