linux-kernel - Re: [RFC PATCH v4 09/10] KVM: x86: Make struct sev_cmd common for KVM_MEM_ENC

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Date:   Fri, 21 Jul 2023 07:51:04 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     isaku.yamahata@...el.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        isaku.yamahata@...il.com, Michael Roth <michael.roth@....com>,
        Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
        Sagi Shahar <sagis@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Kai Huang <kai.huang@...el.com>,
        Zhi Wang <zhi.wang.linux@...il.com>, chen.bo@...el.com,
        linux-coco@...ts.linux.dev,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        Ackerley Tng <ackerleytng@...gle.com>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yuan Yao <yuan.yao@...ux.intel.com>
Subject: Re: [RFC PATCH v4 09/10] KVM: x86: Make struct sev_cmd common for KVM_MEM_ENC_OP

On Thu, Jul 20, 2023, isaku.yamahata@...el.com wrote:
> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> index aa7a56a47564..32883e520b00 100644
> --- a/arch/x86/include/uapi/asm/kvm.h
> +++ b/arch/x86/include/uapi/asm/kvm.h
> @@ -562,6 +562,39 @@ struct kvm_pmu_event_filter {
>  /* x86-specific KVM_EXIT_HYPERCALL flags. */
>  #define KVM_EXIT_HYPERCALL_LONG_MODE	BIT(0)
>  
> +struct kvm_mem_enc_cmd {
> +	/* sub-command id of KVM_MEM_ENC_OP. */
> +	__u32 id;
> +	/*
> +	 * Auxiliary flags for sub-command.  If sub-command doesn't use it,
> +	 * set zero.
> +	 */
> +	__u32 flags;
> +	/*
> +	 * Data for sub-command.  An immediate or a pointer to the actual
> +	 * data in process virtual address.  If sub-command doesn't use it,
> +	 * set zero.
> +	 */
> +	__u64 data;
> +	/*
> +	 * Supplemental error code in the case of error.
> +	 * SEV error code from the PSP or TDX SEAMCALL status code.
> +	 * The caller should set zero.
> +	 */
> +	union {
> +		struct {
> +			__u32 error;
> +			/*
> +			 * KVM_SEV_LAUNCH_START and KVM_SEV_RECEIVE_START
> +			 * require extra data. Not included in struct
> +			 * kvm_sev_launch_start or struct kvm_sev_receive_start.
> +			 */
> +			__u32 sev_fd;
> +		};
> +		__u64 error64;
> +	};
> +};

Eww.  Why not just use an entirely different struct for TDX?  I don't see what
benefit this provides other than a warm fuzzy feeling that TDX and SEV share a
struct.  Practically speaking, KVM will likely take on more work to forcefully
smush the two together than if they're separate things.