Re: [RFC PATCH v4 09/10] KVM: x86: Make struct sev_cmd common for KVM_MEM_ENC_OP

[Xiaoyao Li]

On 7/21/2023 10:51 PM, Sean Christopherson wrote:
> On Thu, Jul 20, 2023, isaku.yamahata@xxxxxxxxx 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.