Re: [RFC PATCH v1 11/30] KVM: arm64: create and use a new vcpu_hyp_state struct

[Quentin Perret <qperret@google.com>]

On Friday 24 Sep 2021 at 13:53:40 (+0100), Fuad Tabba wrote:
> Create a struct for the hypervisor state from the related fields
> in vcpu_arch. This is needed in future patches to reduce the
> scope of functions from the vcpu as a whole to only the relevant
> state, via this newly created struct.
> 
> Create a new instance of this struct in vcpu_arch and fix the
> accessors to use the new fields. Remove the existing fields from
> vcpu_arch.
> 
> Signed-off-by: Fuad Tabba <tabba@google.com>
> ---
>  arch/arm64/include/asm/kvm_host.h | 35 ++++++++++++++++++-------------
>  arch/arm64/kernel/asm-offsets.c   |  2 +-
>  2 files changed, 21 insertions(+), 16 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 3e5c173d2360..dc4b5e133d86 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -269,27 +269,35 @@ struct vcpu_reset_state {
>  	bool		reset;
>  };
>  
> +/* Holds the hyp-relevant data of a vcpu.*/
> +struct vcpu_hyp_state {
> +	/* HYP configuration */
> +	u64 hcr_el2;
> +	u32 mdcr_el2;
> +
> +	/* Virtual SError ESR to restore when HCR_EL2.VSE is set */
> +	u64 vsesr_el2;
> +
> +	/* Exception Information */
> +	struct kvm_vcpu_fault_info fault;
> +
> +	/* Miscellaneous vcpu state flags */
> +	u64 flags;
> +};
> +
>  struct kvm_vcpu_arch {
>  	struct kvm_cpu_context ctxt;
>  	void *sve_state;
>  	unsigned int sve_max_vl;
>  
> +	struct vcpu_hyp_state hyp_state;
> +
>  	/* Stage 2 paging state used by the hardware on next switch */
>  	struct kvm_s2_mmu *hw_mmu;
>  
> -	/* HYP configuration */
> -	u64 hcr_el2;
> -	u32 mdcr_el2;
> -
> -	/* Exception Information */
> -	struct kvm_vcpu_fault_info fault;
> -
>  	/* State of various workarounds, see kvm_asm.h for bit assignment */
>  	u64 workaround_flags;
>  
> -	/* Miscellaneous vcpu state flags */
> -	u64 flags;
> -
>  	/*
>  	 * We maintain more than a single set of debug registers to support
>  	 * debugging the guest from the host and to maintain separate host and
> @@ -356,9 +364,6 @@ struct kvm_vcpu_arch {
>  	/* Detect first run of a vcpu */
>  	bool has_run_once;
>  
> -	/* Virtual SError ESR to restore when HCR_EL2.VSE is set */
> -	u64 vsesr_el2;
> -
>  	/* Additional reset state */
>  	struct vcpu_reset_state	reset_state;
>  
> @@ -373,7 +378,7 @@ struct kvm_vcpu_arch {
>  	} steal;
>  };
>  
> -#define hyp_state(vcpu) ((vcpu)->arch)
> +#define hyp_state(vcpu) ((vcpu)->arch.hyp_state)

Aha, so _that_ is the nice thing about the previous patches ... I need
to stare at this series for a little longer, but wouldn't it be easier
to simply apply the struct kvm_vcpu_arch change and fixup all the users
at once instead of having all these preparatory patches? It's probably
personal preference at this point, but I must admit I'm finding all
these layers of accessors a little confusing. Happy to hear what others
think.

Thanks,
Quentin