linux-kernel - Re: [RFC PATCH v5 027/104] KVM: TDX: initialize VM with TDX specific parameters

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Date:   Thu, 7 Apr 2022 19:18:03 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Kai Huang <kai.huang@...el.com>
Cc:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>, erdemaktas@...gle.com,
        Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 027/104] KVM: TDX: initialize VM with TDX specific
 parameters

On Thu, Mar 31, 2022 at 05:55:01PM +1300,
Kai Huang <kai.huang@...el.com> wrote:

> > diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
> > index 70f9be4ea575..6e26dde0dce6 100644
> > --- a/arch/x86/include/uapi/asm/kvm.h
> > +++ b/arch/x86/include/uapi/asm/kvm.h
> > @@ -531,6 +531,7 @@ struct kvm_pmu_event_filter {
> >  /* Trust Domain eXtension sub-ioctl() commands. */
> >  enum kvm_tdx_cmd_id {
> >  	KVM_TDX_CAPABILITIES = 0,
> > +	KVM_TDX_INIT_VM,
> >  
> >  	KVM_TDX_CMD_NR_MAX,
> >  };
> > @@ -561,4 +562,15 @@ struct kvm_tdx_capabilities {
> >  	struct kvm_tdx_cpuid_config cpuid_configs[0];
> >  };
> >  
> > +struct kvm_tdx_init_vm {
> > +	__u32 max_vcpus;
> > +	__u32 tsc_khz;
> > +	__u64 attributes;
> > +	__u64 cpuid;
> 
> Is it better to append all CPUIDs directly into this structure, perhaps at end
> of this structure, to make it more consistent with TD_PARAMS?
> 
> Also, I think somewhere in commit message or comments we should explain why
> CPUIDs are passed here (why existing KVM_SET_CUPID2 is not sufficient).

Ok, let's change the data structure to match more with TD_PARAMS.


> > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > index 20b45bb0b032..236faaca68a0 100644
> > --- a/arch/x86/kvm/vmx/tdx.c
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -387,6 +387,203 @@ static int tdx_capabilities(struct kvm *kvm, struct kvm_tdx_cmd *cmd)
> >  	return 0;
> >  }
> >  
> > +static struct kvm_cpuid_entry2 *tdx_find_cpuid_entry(struct kvm_tdx *kvm_tdx,
> > +						u32 function, u32 index)
> > +{
> > +	struct kvm_cpuid_entry2 *e;
> > +	int i;
> > +
> > +	for (i = 0; i < kvm_tdx->cpuid_nent; i++) {
> > +		e = &kvm_tdx->cpuid_entries[i];
> > +
> > +		if (e->function == function && (e->index == index ||
> > +		    !(e->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX)))
> > +			return e;
> > +	}
> > +	return NULL;
> > +}
> > +
> > +static int setup_tdparams(struct kvm *kvm, struct td_params *td_params,
> > +			struct kvm_tdx_init_vm *init_vm)
> > +{
> > +	struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm);
> > +	struct tdx_cpuid_config *config;
> > +	struct kvm_cpuid_entry2 *entry;
> > +	struct tdx_cpuid_value *value;
> > +	u64 guest_supported_xcr0;
> > +	u64 guest_supported_xss;
> > +	u32 guest_tsc_khz;
> > +	int max_pa;
> > +	int i;
> > +
> > +	/* init_vm->reserved must be zero */
> > +	if (find_first_bit((unsigned long *)init_vm->reserved,
> > +			   sizeof(init_vm->reserved) * 8) !=
> > +	    sizeof(init_vm->reserved) * 8)
> > +		return -EINVAL;
> > +
> > +	td_params->max_vcpus = init_vm->max_vcpus;
> > +
> > +	td_params->attributes = init_vm->attributes;
> > +	if (td_params->attributes & TDX_TD_ATTRIBUTE_PERFMON) {
> > +		pr_warn("TD doesn't support perfmon. KVM needs to save/restore "
> > +			"host perf registers properly.\n");
> > +		return -EOPNOTSUPP;
> > +	}
> 
> PERFMON can be supported but it's not support in this series, so perhaps add a
> comment to explain it's a TODO?

Yes, good idea. Will do.


> > +	max_pa = 36;
> > +	entry = tdx_find_cpuid_entry(kvm_tdx, 0x80000008, 0);
> > +	if (entry)
> > +		max_pa = entry->eax & 0xff;
> > +
> > +	td_params->eptp_controls = VMX_EPTP_MT_WB;
> > +	if (cpu_has_vmx_ept_5levels() && max_pa > 48) {
> > +		td_params->eptp_controls |= VMX_EPTP_PWL_5;
> > +		td_params->exec_controls |= TDX_EXEC_CONTROL_MAX_GPAW;
> > +	} else {
> > +		td_params->eptp_controls |= VMX_EPTP_PWL_4;
> > +	}
> 
> Not quite sure, but could we support >48 GPA with 4-level EPT?

No.
"5-level paging and 5-level EPT"
section 4.1 4-level EPT
"4-level EPT is limited to translating 48-bit guest-physical addresses."
-- 
Isaku Yamahata <isaku.yamahata@...il.com>