linux-kernel - Re: [PATCH v6 3/5] KVM: PPC: clean up redundant kvm

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Date:   Fri, 10 Jul 2020 09:57:02 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>,
        tsbogend@...ha.franken.de, paulus@...abs.org, 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
Cc:     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 v6 3/5] KVM: PPC: clean up redundant kvm_run parameters in
 assembly

On 23/06/20 15:14, Tianjia Zhang wrote:
>  
>  	/* 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
>  	bl	FUNC(kvmppc_copy_to_svcpu)
>  	nop
> -	REST_GPR(4, r1)
> +	REST_GPR(3, r1)
>  
>  #ifdef CONFIG_PPC_BOOK3S_64
>  	/* Get the dcbz32 flag */
> @@ -146,7 +144,7 @@ after_sprg3_load:

Below, there are a bunch of references to r3 and r4 left

        rldicl  r3, r3, 0, 63           /* r3 &= 1 */
        stb     r3, HSTATE_RESTORE_HID5(r13)

        /* Load up guest SPRG3 value, since it's user readable */
        lwz     r3, VCPU_SHAREDBE(r4)				  <<<
        cmpwi   r3, 0
        ld      r5, VCPU_SHARED(r4)				  <<<

where r3 is also destroyed.  So I'd rather have three patches:

- one that is as small as possible, changing the prototypes and adding

	mr r4, r3

- one that entirely swaps out r3 and r4.  This would be the hard one to
review!

- one that cleans up the prologue and epilogue

But overall I think it's simplest to just leave out this patch.

Paolo