linux-kernel - Re: [PATCH v19 024/130] KVM: TDX: Add placeholders for TDX VM/vcpu structure

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Date: Fri, 22 Mar 2024 10:37:20 +1300
From: "Huang, Kai" <kai.huang@...el.com>
To: "Yamahata, Isaku" <isaku.yamahata@...el.com>, "kvm@...r.kernel.org"
	<kvm@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>, Paolo Bonzini
	<pbonzini@...hat.com>, "Aktas, Erdem" <erdemaktas@...gle.com>, "Sean
 Christopherson" <seanjc@...gle.com>, Sagi Shahar <sagis@...gle.com>, "Chen,
 Bo2" <chen.bo@...el.com>, "Yuan, Hang" <hang.yuan@...el.com>, "Zhang, Tina"
	<tina.zhang@...el.com>
Subject: Re: [PATCH v19 024/130] KVM: TDX: Add placeholders for TDX VM/vcpu
 structure



On 26/02/2024 9:25 pm, Yamahata, Isaku wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> Add placeholders TDX VM/vcpu structure that overlays with VMX VM/vcpu
> structures.  Initialize VM structure size and vcpu size/align so that x86
> KVM common code knows those size irrespective of VMX or TDX.  Those
> structures will be populated as guest creation logic develops.
> 
> Add helper functions to check if the VM is guest TD and add conversion
> functions between KVM VM/VCPU and TDX VM/VCPU.

The changelog is essentially only saying "doing what" w/o "why".

Please at least explain why you invented the 'struct kvm_tdx' and 
'struct vcpu_tdx', and why they are invented in this way.

E.g., can we extend 'struct kvm_vmx' for TDX?

struct kvm_tdx {
	struct kvm_vmx vmx;
	...
};

> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> ---
> v19:
> - correctly update ops.vm_size, vcpu_size and, vcpu_align by Xiaoyao
> 
> v14 -> v15:
> - use KVM_X86_TDX_VM
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>   arch/x86/kvm/vmx/main.c | 14 ++++++++++++
>   arch/x86/kvm/vmx/tdx.c  |  1 +
>   arch/x86/kvm/vmx/tdx.h  | 50 +++++++++++++++++++++++++++++++++++++++++
>   3 files changed, 65 insertions(+)
>   create mode 100644 arch/x86/kvm/vmx/tdx.h
> 
> diff --git a/arch/x86/kvm/vmx/main.c b/arch/x86/kvm/vmx/main.c
> index 18aef6e23aab..e11edbd19e7c 100644
> --- a/arch/x86/kvm/vmx/main.c
> +++ b/arch/x86/kvm/vmx/main.c
> @@ -5,6 +5,7 @@
>   #include "vmx.h"
>   #include "nested.h"
>   #include "pmu.h"
> +#include "tdx.h"
>   
>   static bool enable_tdx __ro_after_init;
>   module_param_named(tdx, enable_tdx, bool, 0444);
> @@ -18,6 +19,9 @@ static __init int vt_hardware_setup(void)
>   		return ret;
>   
>   	enable_tdx = enable_tdx && !tdx_hardware_setup(&vt_x86_ops);
> +	if (enable_tdx)
> +		vt_x86_ops.vm_size = max_t(unsigned int, vt_x86_ops.vm_size,
> +					   sizeof(struct kvm_tdx));
>   

Now I see why you included 'struct kvm_x86_ops' as function parameter.

Please move it to this patch.

>   	return 0;
>   }
> @@ -215,8 +219,18 @@ static int __init vt_init(void)
>   	 * Common KVM initialization _must_ come last, after this, /dev/kvm is
>   	 * exposed to userspace!
>   	 */
> +	/*
> +	 * kvm_x86_ops is updated with vt_x86_ops.  vt_x86_ops.vm_size must
> +	 * be set before kvm_x86_vendor_init().
> +	 */
>   	vcpu_size = sizeof(struct vcpu_vmx);
>   	vcpu_align = __alignof__(struct vcpu_vmx);
> +	if (enable_tdx) {
> +		vcpu_size = max_t(unsigned int, vcpu_size,
> +				  sizeof(struct vcpu_tdx));
> +		vcpu_align = max_t(unsigned int, vcpu_align,
> +				   __alignof__(struct vcpu_tdx));
> +	}

Since you are updating vm_size in vt_hardware_setup(), I am wondering 
whether we can do similar thing for vcpu_size and vcpu_align.

That is, we put them both to 'struct kvm_x86_ops', and you update them 
in vt_hardware_setup().

kvm_init() can then just access them directly in this way both 
'vcpu_size' and 'vcpu_align' function parameters can be removed.


>   	r = kvm_init(vcpu_size, vcpu_align, THIS_MODULE);
>   	if (r)
>   		goto err_kvm_init;