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

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Message-ID: <20200526055924.GD282305@thinks.paulus.ozlabs.org>
Date:   Tue, 26 May 2020 15:59:24 +1000
From:   Paul Mackerras <paulus@...abs.org>
To:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
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 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?

> 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.