linux-kernel - Re: [PATCH v7 025/102] KVM: TDX: initialize VM with TDX specific parameters

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Message-ID: <dd6a51df-995c-6793-3988-b096188cd447@intel.com>
Date:   Tue, 28 Jun 2022 16:30:53 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v7 025/102] KVM: TDX: initialize VM with TDX specific
 parameters

On 6/28/2022 5:53 AM, isaku.yamahata@...el.com wrote:
> From: Xiaoyao Li <xiaoyao.li@...el.com>
> 
> TDX requires additional parameters for TDX VM for confidential execution to
> protect its confidentiality of its memory contents and its CPU state from
> any other software, including VMM. When creating guest TD VM before
> creating vcpu, the number of vcpu, TSC frequency (that is same among
> vcpus. and it can't be changed.)  CPUIDs which is emulated by the TDX
> module. It means guest can trust those CPUIDs. and sha384 values for
> measurement.
> 
> Add new subcommand, KVM_TDX_INIT_VM, to pass parameters for TDX guest.  It
> assigns encryption key to the TDX guest for memory encryption.  TDX
> encrypts memory per-guest bases.  It assigns device model passes per-VM
> parameters for the TDX guest.  The maximum number of vcpus, tsc frequency
> (TDX guest has fised VM-wide TSC frequency. not per-vcpu.  The TDX guest
> can not change it.), attributes (production or debug), available extended
> features (which is reflected into guest XCR0, IA32_XSS MSR), cpuids, sha384
> measurements, and etc.
> 
> This subcommand is called before creating vcpu and KVM_SET_CPUID2, i.e.
> cpuids configurations aren't available yet.  So CPUIDs configuration values
> needs to be passed in struct kvm_init_vm.  It's device model responsibility
> to make this cpuid config for KVM_TDX_INIT_VM and KVM_SET_CPUID2.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>   arch/x86/include/asm/kvm_host.h       |   2 +
>   arch/x86/include/asm/tdx.h            |   3 +
>   arch/x86/include/uapi/asm/kvm.h       |  33 +++++
>   arch/x86/kvm/vmx/tdx.c                | 206 ++++++++++++++++++++++++++
>   arch/x86/kvm/vmx/tdx.h                |  23 +++
>   tools/arch/x86/include/uapi/asm/kvm.h |  33 +++++
>   6 files changed, 300 insertions(+)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 342decc69649..81638987cdb9 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1338,6 +1338,8 @@ struct kvm_arch {
>   	 * the global KVM_MAX_VCPU_IDS may lead to significant memory waste.
>   	 */
>   	u32 max_vcpu_ids;
> +
> +	gfn_t gfn_shared_mask;

I think it's better to put in a seperate patch or the patch that 
consumes it.

>   };
>   
...

> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 2a9dfd54189f..1273b60a1a00 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -438,6 +438,209 @@ int tdx_dev_ioctl(void __user *argp)
>   	return 0;
>   }
>   
> +/*
> + * cpuid entry lookup in TDX cpuid config way.
> + * The difference is how to specify index(subleaves).
> + * Specify index to TDX_CPUID_NO_SUBLEAF for CPUID leaf with no-subleaves.
> + */
> +static const struct kvm_cpuid_entry2 *tdx_find_cpuid_entry(
> +	const struct kvm_cpuid2 *cpuid, u32 function, u32 index)
> +{
> +	int i;
> +
> +

superfluous line

> +	/* In TDX CPU CONFIG, TDX_CPUID_NO_SUBLEAF means index = 0. */
> +	if (index == TDX_CPUID_NO_SUBLEAF)
> +		index = 0;
> +
> +	for (i = 0; i < cpuid->nent; i++) {
> +		const struct kvm_cpuid_entry2 *e = &cpuid->entries[i];
> +
> +		if (e->function == function &&
> +		    (e->index == index ||
> +		     !(e->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX)))
> +			return e;
> +	}
> +	return NULL;
> +}

no need for kvm_tdx->tsc_khz field. We have kvm->arch.default_tsc_khz.
It seems kvm_tdx->tsc_khz is not used in the following patches.

...

> +
> +	kvm_tdx->tsc_offset = td_tdcs_exec_read64(kvm_tdx, TD_TDCS_EXEC_TSC_OFFSET);
> +	kvm_tdx->attributes = td_params->attributes;
> +	kvm_tdx->xfam = td_params->xfam;
> +	kvm_tdx->tsc_khz = TDX_TSC_25MHZ_TO_KHZ(td_params->tsc_frequency);
> +	kvm->max_vcpus = td_params->max_vcpus;
> +
> +	if (td_params->exec_controls & TDX_EXEC_CONTROL_MAX_GPAW)
> +		kvm->arch.gfn_shared_mask = gpa_to_gfn(BIT_ULL(51));
> +	else
> +		kvm->arch.gfn_shared_mask = gpa_to_gfn(BIT_ULL(47));
> +

....

> diff --git a/tools/arch/x86/include/uapi/asm/kvm.h b/tools/arch/x86/include/uapi/asm/kvm.h
> index a9ea3573be1b..779dfd683d66 100644
> --- a/tools/arch/x86/include/uapi/asm/kvm.h
> +++ b/tools/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,
>   };
> @@ -576,4 +577,36 @@ struct kvm_tdx_capabilities {
>   	struct kvm_tdx_cpuid_config cpuid_configs[0];
>   };
>   
> +struct kvm_tdx_init_vm {
> +	__u64 attributes;
> +	__u32 max_vcpus;
> +	__u32 tsc_khz;

it needs to align with arch/x86/include/uapi/asm/kvm.h that @tsc_khz 
needs to be removed.