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

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Message-ID: <9e8a98ad-1f8d-a09c-3173-71c5c3ab5ed4@intel.com>
Date:   Tue, 25 Jul 2023 17:07:06 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Sean Christopherson <seanjc@...gle.com>, 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 7/21/2023 10:51 PM, Sean Christopherson wrote:
> 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.

generalizing the struct of KVM_MEM_ENC_OP should be the first step. The 
final target should be generalizing a set of commands for confidential 
VMs (SEV-* VMs and TDs, maybe even for other arches), e.g., the commands 
to create a confidential VM and commands to live migration a 
confidential VM.

However, there seems not small divergence between the commands to create 
a SEV-* VM and TDX VMs. I'm not sure if it is worth investigating and 
pursuing.