linux-kernel - Re: [PATCH v19 039/130] KVM: TDX: initialize VM with TDX specific parameters

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Date: Fri, 22 Mar 2024 11:20:01 +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: "Zhang, Tina" <tina.zhang@...el.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "Yuan, Hang" <hang.yuan@...el.com>, "Chen, Bo2"
	<chen.bo@...el.com>, "sagis@...gle.com" <sagis@...gle.com>,
	"isaku.yamahata@...il.com" <isaku.yamahata@...il.com>, "Aktas, Erdem"
	<erdemaktas@...gle.com>, "Li, Xiaoyao" <xiaoyao.li@...el.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>
Subject: Re: [PATCH v19 039/130] KVM: TDX: initialize VM with TDX specific
 parameters

On Mon, 2024-02-26 at 00:25 -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];	/* sha384 digest */
> +	/*
> +	 * For future extensibility to make sizeof(struct kvm_tdx_init_vm) = 8KB.
> +	 * This should be enough given sizeof(TD_PARAMS) = 1024.
> +	 * 8KB was chosen given because
> +	 * sizeof(struct kvm_cpuid_entry2) * KVM_MAX_CPUID_ENTRIES(=256) = 8KB.
> +	 */
> +	__u64 reserved[1004];

This is insane.

You said you want to reserve 8K for CPUID entries, but how can these 1004 * 8
bytes be used for CPUID entries since ...

> +
> +	/*
> +	 * Call KVM_TDX_INIT_VM before vcpu creation, thus before
> +	 * KVM_SET_CPUID2.
> +	 * This configuration supersedes KVM_SET_CPUID2s for VCPUs because the
> +	 * TDX module directly virtualizes those CPUIDs without VMM.  The user
> +	 * space VMM, e.g. qemu, should make KVM_SET_CPUID2 consistent with
> +	 * those values.  If it doesn't, KVM may have wrong idea of vCPUIDs of
> +	 * the guest, and KVM may wrongly emulate CPUIDs or MSRs that the TDX
> +	 * module doesn't virtualize.
> +	 */
> +	struct kvm_cpuid2 cpuid;

... they are actually placed right after here?

> +};
> +