linux-kernel - Re: [PATCH v7 08/11] KVM: arm64: introduce vcpu->arch.debug

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Message-ID: <87mvzdsoer.fsf@linaro.org>
Date:	Fri, 03 Jul 2015 08:14:52 +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, Gleb Natapov <gleb@...nel.org>,
	Russell King <linux@....linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Richard Weinberger <richard@....at>,
	Andre Przywara <andre.przywara@....com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7 08/11] KVM: arm64: introduce vcpu->arch.debug_ptr


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

> On Wed, Jul 01, 2015 at 07:29:00PM +0100, Alex Bennée wrote:
>> This introduces a level of indirection for the debug registers. Instead
>> of using the sys_regs[] directly we store registers in a structure in
>> the vcpu. The new kvm_arm_reset_debug_ptr() sets the debug ptr to the
>> guest context.
>> 
>> This also entails updating the sys_regs code to access this new
>> structure. New access function have been added for each set of debug
>> registers. The generic functions are still used for the few registers
>> stored in the main context.
>> 
>> New access function pointers have been added to the sys_reg_desc
>> structure to support the GET/SET_ONE_REG ioctl operations.
>
> Why is this needed?

Previously I had a hacky:

	if (r->access == trap_debug64)
		return debug_get64(vcpu, r, reg, uaddr);

Which used the same offset information. Now we have a cleaner:

	if (r->set)
		return (r->set)(vcpu, r, reg, uaddr);

Which accesses the structure directly, as the trap functions do:

	__u64 *r = &vcpu->arch.vcpu_debug_state.dbg_bvr[rd->reg];
	if (copy_from_user(uaddr, r, KVM_REG_SIZE(reg->id)) != 0)
		return -EFAULT;
	return 0;

<snip>
>> +#if 0
>> +static int debug_set64(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
>> +		const struct kvm_one_reg *reg, void __user *uaddr)
>> +{
>> +	__u64 *r = (__u64 *) ((void * )&vcpu->arch.vcpu_debug_state + rd->reg);
>> +	if (copy_from_user(uaddr, r, KVM_REG_SIZE(reg->id)) != 0)
>> +		return -EFAULT;
>> +	return 0;
>> +}
>> +
>> +static int debug_get64(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
>> +	const struct kvm_one_reg *reg, void __user *uaddr)
>> +{
>> +	__u64 *r = (__u64 *) ((void * )&vcpu->arch.vcpu_debug_state + rd->reg);
>> +	if (copy_to_user(uaddr, r, KVM_REG_SIZE(reg->id)) != 0)
>> +		return -EFAULT;
>> +	return 0;
>> +}
>> +#endif
>> +
>
> what is this ifdef'ed block of code doing here?

Oops. Yeah looks like I missed removing that after I finished the
re-factor. These where the old get/set functions I used.

>
>>  int kvm_arm_sys_reg_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>>  {
>>  	const struct sys_reg_desc *r;
>> @@ -1303,6 +1530,9 @@ int kvm_arm_sys_reg_get_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg
>>  	if (!r)
>>  		return get_invariant_sys_reg(reg->id, uaddr);
>>  
>> +	if (r->get)
>> +		return (r->get)(vcpu, r, reg, uaddr);
>> +
>>  	return reg_to_user(uaddr, &vcpu_sys_reg(vcpu, r->reg), reg->id);
>>  }
>>  
>> @@ -1321,6 +1551,9 @@ int kvm_arm_sys_reg_set_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg
>>  	if (!r)
>>  		return set_invariant_sys_reg(reg->id, uaddr);
>>  
>> +	if (r->set)
>> +		return (r->set)(vcpu, r, reg, uaddr);
>> +
>>  	return reg_from_user(&vcpu_sys_reg(vcpu, r->reg), uaddr, reg->id);
>>  }
>>  
>> diff --git a/arch/arm64/kvm/sys_regs.h b/arch/arm64/kvm/sys_regs.h
>> index d411e25..9265e7d 100644
>> --- a/arch/arm64/kvm/sys_regs.h
>> +++ b/arch/arm64/kvm/sys_regs.h
>> @@ -55,6 +55,12 @@ struct sys_reg_desc {
>>  
>>  	/* Value (usually reset value) */
>>  	u64 val;
>> +
>> +	/* Get/Set functions, fallback if NULL */
>
> Is this only meant for usersapce access or when should one use these?

Yes for GET/SET

>
>> +	int (*get)(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
>> +		   const struct kvm_one_reg *reg, void __user *uaddr);
>> +	int (*set)(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
>> +		   const struct kvm_one_reg *reg, void __user *uaddr);
>>  };
>>  
>>  static inline void print_sys_reg_instr(const struct sys_reg_params *p)
>> -- 
>> 2.4.5
>> 

-- 
Alex Bennée
--
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