Subject: [PATCH] ARM: KVM: Cleanup exception injection

From: [email-masked] (Marc Zyngier)
Date: Thu, 17 Dec 2015 08:59:38 +0000

On 16/12/15 20:40, Christoffer Dall wrote:
> On Mon, Dec 14, 2015 at 06:06:36PM +0000, Marc Zyngier wrote:
>> David Binderman reported that the exception injection code had a
>> couple of unused variables lingering around.
>>
>> Upon examination, it looked like this code could do with an
>> anticipated spring cleaning, which amounts to deduplicating
>> the CPSR/SPSR update.
>>
>> The spurious variables are removed in the process.
>>
>> Reported-by: David Binderman <[email-masked]>
>> Signed-off-by: Marc Zyngier <[email-masked]>
>> ---
>>  arch/arm/kvm/emulate.c | 59 ++++++++++++++++++++------------------------------
>>  1 file changed, 23 insertions(+), 36 deletions(-)
>>
>> diff --git a/arch/arm/kvm/emulate.c b/arch/arm/kvm/emulate.c
>> index d6c0052..245106e 100644
>> --- a/arch/arm/kvm/emulate.c
>> +++ b/arch/arm/kvm/emulate.c
>> @@ -275,6 +275,25 @@ static u32 exc_vector_base(struct kvm_vcpu *vcpu)
>>  		return vbar;
>>  }
>>  
>> +/* Switch to an exception mode, updating both CPSR and SPSR */
>> +static void kvm_update_psr(struct kvm_vcpu *vcpu, unsigned long mode)
>> +{
>> +	unsigned long cpsr = *vcpu_cpsr(vcpu);
>> +	u32 sctlr = vcpu->arch.cp15[c1_SCTLR];
>> +
>> +	*vcpu_cpsr(vcpu) = (cpsr & ~MODE_MASK) | mode;
>> +	*vcpu_cpsr(vcpu) |= PSR_I_BIT;
>> +	*vcpu_cpsr(vcpu) &= ~(PSR_IT_MASK | PSR_J_BIT | PSR_E_BIT | PSR_T_BIT);
>> +
>> +	if (sctlr & SCTLR_TE)
>> +		*vcpu_cpsr(vcpu) |= PSR_T_BIT;
>> +	if (sctlr & SCTLR_EE)
>> +		*vcpu_cpsr(vcpu) |= PSR_E_BIT;
>> +
>> +	/* Note: These now point to the mode banked copies */
>> +	*vcpu_spsr(vcpu) = cpsr;
>> +}
>> +
>>  /**
>>   * kvm_inject_undefined - inject an undefined exception into the guest
>>   * @vcpu: The VCPU to receive the undefined exception
>> @@ -286,29 +305,13 @@ static u32 exc_vector_base(struct kvm_vcpu *vcpu)
>>   */
>>  void kvm_inject_undefined(struct kvm_vcpu *vcpu)
>>  {
>> -	unsigned long new_lr_value;
>> -	unsigned long new_spsr_value;
>>  	unsigned long cpsr = *vcpu_cpsr(vcpu);
>> -	u32 sctlr = vcpu->arch.cp15[c1_SCTLR];
>>  	bool is_thumb = (cpsr & PSR_T_BIT);
>>  	u32 vect_offset = 4;
>>  	u32 return_offset = (is_thumb) ? 2 : 4;
>>  
>> -	new_spsr_value = cpsr;
>> -	new_lr_value = *vcpu_pc(vcpu) - return_offset;
>> -
>> -	*vcpu_cpsr(vcpu) = (cpsr & ~MODE_MASK) | UND_MODE;
>> -	*vcpu_cpsr(vcpu) |= PSR_I_BIT;
>> -	*vcpu_cpsr(vcpu) &= ~(PSR_IT_MASK | PSR_J_BIT | PSR_E_BIT | PSR_T_BIT);
>> -
>> -	if (sctlr & SCTLR_TE)
>> -		*vcpu_cpsr(vcpu) |= PSR_T_BIT;
>> -	if (sctlr & SCTLR_EE)
>> -		*vcpu_cpsr(vcpu) |= PSR_E_BIT;
>> -
>> -	/* Note: These now point to UND banked copies */
>> -	*vcpu_spsr(vcpu) = cpsr;
>> -	*vcpu_reg(vcpu, 14) = new_lr_value;
>> +	kvm_update_psr(vcpu, UND_MODE);
>> +	*vcpu_reg(vcpu, 14) = *vcpu_pc(vcpu) - return_offset;
>>  
>>  	/* Branch to exception vector */
>>  	*vcpu_pc(vcpu) = exc_vector_base(vcpu) + vect_offset;
>> @@ -320,30 +323,14 @@ void kvm_inject_undefined(struct kvm_vcpu *vcpu)
>>   */
>>  static void inject_abt(struct kvm_vcpu *vcpu, bool is_pabt, unsigned long addr)
>>  {
>> -	unsigned long new_lr_value;
>> -	unsigned long new_spsr_value;
>>  	unsigned long cpsr = *vcpu_cpsr(vcpu);
>> -	u32 sctlr = vcpu->arch.cp15[c1_SCTLR];
>>  	bool is_thumb = (cpsr & PSR_T_BIT);
>>  	u32 vect_offset;
>>  	u32 return_offset = (is_thumb) ? 4 : 0;
>>  	bool is_lpae;
>>  
>> -	new_spsr_value = cpsr;
>> -	new_lr_value = *vcpu_pc(vcpu) + return_offset;
>> -
>> -	*vcpu_cpsr(vcpu) = (cpsr & ~MODE_MASK) | ABT_MODE;
>> -	*vcpu_cpsr(vcpu) |= PSR_I_BIT | PSR_A_BIT;
> 
> seems like you're losing the PSR_A_BIT in kvm_update_psr() now?

Ah, nice catch. Indeed, CPSR.A gets set on abort entry, but not on
undef. I'll add a check in kvm_update_psr, with a reference to the
AArch32.EnterMode() pseudocode from the ARMv8 ARM.

> 
>> -	*vcpu_cpsr(vcpu) &= ~(PSR_IT_MASK | PSR_J_BIT | PSR_E_BIT | PSR_T_BIT);
>> -
>> -	if (sctlr & SCTLR_TE)
>> -		*vcpu_cpsr(vcpu) |= PSR_T_BIT;
>> -	if (sctlr & SCTLR_EE)
>> -		*vcpu_cpsr(vcpu) |= PSR_E_BIT;
>> -
>> -	/* Note: These now point to ABT banked copies */
>> -	*vcpu_spsr(vcpu) = cpsr;
>> -	*vcpu_reg(vcpu, 14) = new_lr_value;
>> +	kvm_update_psr(vcpu, ABT_MODE);
>> +	*vcpu_reg(vcpu, 14) = *vcpu_pc(vcpu) + return_offset;
>>  
>>  	if (is_pabt)
>>  		vect_offset = 12;
>> -- 
>> 2.1.4
>>
> 
> Otherwise looks like a welcome cleanup!
> 
> Thanks,
> -Christoffer
> 

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...