linux-kernel - Re: [RFC PATCH 08/27] KVM: arm64: Make kvm_call

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Date:   Mon, 23 Nov 2020 12:51:53 +0000
From:   David Brazdil <dbrazdil@...gle.com>
To:     Quentin Perret <qperret@...gle.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:KERNEL VIRTUAL MACHINE FOR ARM64 (KVM/arm64)" 
        <kvmarm@...ts.cs.columbia.edu>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE" 
        <devicetree@...r.kernel.org>, kernel-team@...roid.com,
        android-kvm@...gle.com
Subject: Re: [RFC PATCH 08/27] KVM: arm64: Make kvm_call_hyp() a function
 call at Hyp

On Tue, Nov 17, 2020 at 06:15:48PM +0000, 'Quentin Perret' via kernel-team wrote:
> kvm_call_hyp() has some logic to issue a function call or a hypercall
> depending the EL at which the kernel is running. However, all the code
> compiled under __KVM_NVHE_HYPERVISOR__ is guaranteed to run only at EL2,
> and in this case a simple function call is needed.
> 
> Add ifdefery to kvm_host.h to symplify kvm_call_hyp() in .hyp.text.
> 
> Signed-off-by: Quentin Perret <qperret@...gle.com>
> ---
>  arch/arm64/include/asm/kvm_host.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index ac11adab6602..7a5d5f4b3351 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -557,6 +557,7 @@ int kvm_test_age_hva(struct kvm *kvm, unsigned long hva);
>  void kvm_arm_halt_guest(struct kvm *kvm);
>  void kvm_arm_resume_guest(struct kvm *kvm);
>  
> +#ifndef __KVM_NVHE_HYPERVISOR__
>  #define kvm_call_hyp_nvhe(f, ...)						\
>  	({								\
>  		struct arm_smccc_res res;				\
> @@ -596,6 +597,11 @@ void kvm_arm_resume_guest(struct kvm *kvm);
>  									\
>  		ret;							\
>  	})
> +#else /* __KVM_NVHE_HYPERVISOR__ */
> +#define kvm_call_hyp(f, ...) f(__VA_ARGS__)
> +#define kvm_call_hyp_ret(f, ...) f(__VA_ARGS__)
> +#define kvm_call_hyp_nvhe(f, ...) f(__VA_ARGS__)
> +#endif /* __KVM_NVHE_HYPERVISOR__ */

I was hoping we could define this as the following instead. That would require
adding host-side declarations of all functions currently called with _nvhe.

#define kvm_call_hyp_nvhe(f, ...)					\
+	is_nvhe_hyp_code() ? f(__VA_ARGS__) :				\
	({								\
		struct arm_smccc_res res;				\
									\
		arm_smccc_1_1_hvc(KVM_HOST_SMCCC_FUNC(f),		\
				##__VA_ARGS__, &res);			\
		WARN_ON(res.a0 != SMCCC_RET_SUCCESS);			\
									\
		res.a1;							\
	})

Up to you what you think is cleaner, just my 2 cents...