linux-kernel - Re: [PATCH v4 5/7] KVM: PPC: clean up redundant kvm

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Date:   Mon, 13 Jul 2020 11:07:18 +0800
From:   Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
To:     Paul Mackerras <paulus@...abs.org>
Cc:     pbonzini@...hat.com, tsbogend@...ha.franken.de, mpe@...erman.id.au,
        benh@...nel.crashing.org, borntraeger@...ibm.com,
        frankja@...ux.ibm.com, david@...hat.com, cohuck@...hat.com,
        heiko.carstens@...ibm.com, gor@...ux.ibm.com,
        sean.j.christopherson@...el.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, maz@...nel.org, james.morse@....com,
        julien.thierry.kdev@...il.com, suzuki.poulose@....com,
        christoffer.dall@....com, peterx@...hat.com, thuth@...hat.com,
        chenhuacai@...il.com, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm-ppc@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 5/7] KVM: PPC: clean up redundant kvm_run parameters in
 assembly



On 2020/5/26 13:59, Paul Mackerras wrote:
> On Mon, Apr 27, 2020 at 12:35:12PM +0800, Tianjia Zhang wrote:
>> In the current kvm version, 'kvm_run' has been included in the 'kvm_vcpu'
>> structure. For historical reasons, many kvm-related function parameters
>> retain the 'kvm_run' and 'kvm_vcpu' parameters at the same time. This
>> patch does a unified cleanup of these remaining redundant parameters.
> 
> Some of these changes don't look completely correct to me, see below.
> If you're expecting these patches to go through my tree, I can fix up
> the patch and commit it (with you as author), noting the changes I
> made in the commit message.  Do you want me to do that?
> 

I am very glad for you to do so, although I have submitted a new version 
of patch, I still prefer you to fix up and commit it.

Thanks and best,
Tianjia

>> diff --git a/arch/powerpc/kvm/book3s_interrupts.S b/arch/powerpc/kvm/book3s_interrupts.S
>> index f7ad99d972ce..0eff749d8027 100644
>> --- a/arch/powerpc/kvm/book3s_interrupts.S
>> +++ b/arch/powerpc/kvm/book3s_interrupts.S
>> @@ -55,8 +55,7 @@
>>    ****************************************************************************/
>>   
>>   /* Registers:
>> - *  r3: kvm_run pointer
>> - *  r4: vcpu pointer
>> + *  r3: vcpu pointer
>>    */
>>   _GLOBAL(__kvmppc_vcpu_run)
>>   
>> @@ -68,8 +67,8 @@ kvm_start_entry:
>>   	/* Save host state to the stack */
>>   	PPC_STLU r1, -SWITCH_FRAME_SIZE(r1)
>>   
>> -	/* Save r3 (kvm_run) and r4 (vcpu) */
>> -	SAVE_2GPRS(3, r1)
>> +	/* Save r3 (vcpu) */
>> +	SAVE_GPR(3, r1)
>>   
>>   	/* Save non-volatile registers (r14 - r31) */
>>   	SAVE_NVGPRS(r1)
>> @@ -82,11 +81,11 @@ kvm_start_entry:
>>   	PPC_STL	r0, _LINK(r1)
>>   
>>   	/* Load non-volatile guest state from the vcpu */
>> -	VCPU_LOAD_NVGPRS(r4)
>> +	VCPU_LOAD_NVGPRS(r3)
>>   
>>   kvm_start_lightweight:
>>   	/* Copy registers into shadow vcpu so we can access them in real mode */
>> -	mr	r3, r4
>> +	mr	r4, r3
> 
> This mr doesn't seem necessary.
> 
>>   	bl	FUNC(kvmppc_copy_to_svcpu)
>>   	nop
>>   	REST_GPR(4, r1)
> 
> This should be loading r4 from GPR3(r1), not GPR4(r1) - which is what
> REST_GPR(4, r1) will do.
> 
> Then, in the file but not in the patch context, there is this line:
> 
> 	PPC_LL	r3, GPR4(r1)		/* vcpu pointer */
> 
> where once again GPR4 needs to be GPR3.
> 
>> @@ -191,10 +190,10 @@ after_sprg3_load:
>>   	PPC_STL	r31, VCPU_GPR(R31)(r7)
>>   
>>   	/* Pass the exit number as 3rd argument to kvmppc_handle_exit */
> 
> The comment should be modified to say "2nd" instead of "3rd",
> otherwise it is confusing.
> 
> The rest of the patch looks OK.
> 
> Paul.
>