linux-kernel - Re: [PATCH v11 019/113] KVM: TDX: initialize VM with TDX specific parameters

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Message-ID: <426aa7c48100b4577dd107ca54896286c60b9d4e.camel@intel.com>
Date:   Mon, 16 Jan 2023 10:04:19 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>
CC:     "Li, Xiaoyao" <xiaoyao.li@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
Subject: Re: [PATCH v11 019/113] KVM: TDX: initialize VM with TDX specific
 parameters

On Thu, 2023-01-12 at 08:31 -0800, isaku.yamahata@...el.com wrote:
> +struct kvm_tdx_init_vm {
> +	__u64 attributes;
> +	__u64 mrconfigid[6];	/* sha384 digest */
> +	__u64 mrowner[6];	/* sha384 digest */
> +	__u64 mrownerconfig[6];	/* sha348 digest */
> +	union {
> +		/*
> +		 * KVM_TDX_INIT_VM is called before vcpu creation, thus before
> +		 * KVM_SET_CPUID2.  CPUID configurations needs to be passed.
> +		 *
> +		 * This configuration supersedes KVM_SET_CPUID{,2}.

What does "{,2}" mean?

> +		 * The user space VMM, e.g. qemu, should make them consistent
> +		 * with this values.

You are already using 'struct kvm_cpuid2' below.  Isn't it enough to imply that
userspace should organize data in the format of 'struct kvm_cpuid2'?

> +		 * sizeof(struct kvm_cpuid_entry2) * KVM_MAX_CPUID_ENTRIES(256)
> +		 * = 8KB.
> +		 */

What does this comment try to imply?

> +		struct {
> +			struct kvm_cpuid2 cpuid;
> +			/* 8KB with KVM_MAX_CPUID_ENTRIES. */
> +			struct kvm_cpuid_entry2 entries[];

I don't understand what's the purpose of the second field?

Shouldn't the 'struct kvm_cpuid2' already have all the CPUID entries?

> +		};
> +		/*
> +		 * For future extensibility.
> +		 * The size(struct kvm_tdx_init_vm) = 16KB.
> +		 * This should be enough given sizeof(TD_PARAMS) = 1024
> +		 */
> +		__u64 reserved[2029];

I think this is just wrong.  How can you extend something after a dynamic size
CPUID array?

If you want extensibility, you need to put the space before the flexible array.

> +	};
> +};