linux-kernel - Re: [PATCH RFCv2 4/9] kvm/arm64: Detach ESR operator from vCPU struct

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Date:   Tue, 26 May 2020 11:51:54 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Gavin Shan <gshan@...hat.com>
Cc:     kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, maz@...nel.org, will@...nel.org,
        catalin.marinas@....com, james.morse@....com,
        suzuki.poulose@....com, drjones@...hat.com, eric.auger@...hat.com,
        aarcange@...hat.com, shan.gavin@...il.com
Subject: Re: [PATCH RFCv2 4/9] kvm/arm64: Detach ESR operator from vCPU struct

On Fri, May 08, 2020 at 01:29:14PM +1000, Gavin Shan wrote:
> There are a set of inline functions defined in kvm_emulate.h. Those
> functions reads ESR from vCPU fault information struct and then operate
> on it. So it's tied with vCPU fault information and vCPU struct. It
> limits their usage scope.
> 
> This detaches these functions from the vCPU struct. With this, the
> caller has flexibility on where the ESR is read. It shouldn't cause
> any functional changes.
> 
> Signed-off-by: Gavin Shan <gshan@...hat.com>
> ---
>  arch/arm64/include/asm/kvm_emulate.h     | 83 +++++++++++-------------
>  arch/arm64/kvm/handle_exit.c             | 20 ++++--
>  arch/arm64/kvm/hyp/switch.c              | 24 ++++---
>  arch/arm64/kvm/hyp/vgic-v2-cpuif-proxy.c |  7 +-
>  arch/arm64/kvm/inject_fault.c            |  4 +-
>  arch/arm64/kvm/sys_regs.c                | 12 ++--
>  virt/kvm/arm/arm.c                       |  4 +-
>  virt/kvm/arm/hyp/aarch32.c               |  2 +-
>  virt/kvm/arm/hyp/vgic-v3-sr.c            |  5 +-
>  virt/kvm/arm/mmio.c                      | 27 ++++----
>  virt/kvm/arm/mmu.c                       | 22 ++++---
>  11 files changed, 112 insertions(+), 98 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index bd1a69e7c104..2873bf6dc85e 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -270,10 +270,8 @@ static __always_inline u32 kvm_vcpu_get_esr(const struct kvm_vcpu *vcpu)
>  	return vcpu->arch.fault.esr_el2;
>  }
>  
> -static __always_inline int kvm_vcpu_get_condition(const struct kvm_vcpu *vcpu)
> +static __always_inline int kvm_vcpu_get_condition(u32 esr)

Given the `vcpu` argument has been removed, it's odd to keep `vcpu` in the
name, rather than `esr`.

e.g. this would make more sense as something like esr_get_condition().

... and if we did something like that, we could move most of the
extraction functions into <asm/esr.h>, and share them with non-KVM code.

Otherwise, do you need to extract all of these for your use-case, or do
you only need a few of the helpers? If you only need a few, it might be
better to only factor those out for now, and keep the existing API in
place with wrappers, e.g. have:

| esr_get_condition(u32 esr) {
| 	... 
| }
| 
| kvm_vcpu_get_condition(const struct kvm_vcpu *vcpu)
| {
| 	return esr_get_condition(kvm_vcpu_get_esr(vcpu));
| }

Thanks,
Mark.