linux-kernel - Re: [PATCH v8 004/103] KVM: VMX: Move out vmx_x86

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Date:   Tue, 9 Aug 2022 16:38:10 +0800
From:   Binbin Wu <binbin.wu@...ux.intel.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>,
        erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
        Sagi Shahar <sagis@...gle.com>
Subject: Re: [PATCH v8 004/103] KVM: VMX: Move out vmx_x86_ops to 'main.c' to
 wrap VMX and TDX


On 2022/8/8 6:00, isaku.yamahata@...el.com wrote:
> From: Sean Christopherson <sean.j.christopherson@...el.com>
>
> KVM accesses Virtual Machine Control Structure (VMCS) with VMX instructions
> to operate on VM.  TDX defines its data structure and TDX SEAMCALL APIs for
> VMM to operate on Trust Domain (TD) instead.
>
> Trust Domain Virtual Processor State (TDVPS) is the root control structure
> of a TD VCPU.  It helps the TDX module control the operation of the VCPU,
> and holds the VCPU state while the VCPU is not running. TDVPS is opaque to
> software and DMA access, accessible only by using the TDX module interface
> functions (such as TDH.VP.RD, TDH.VP.WR ,..).  TDVPS includes TD VMCS, and
> TD VMCS auxiliary structures, such as virtual APIC page, virtualization
> exception information, etc.  TDVPS is composed of Trust Domain Virtual
> Processor Root (TDVPR) which is the root page of TDVPS and Trust Domain
> Virtual Processor eXtension (TDVPX) pages which extend TDVPR to help
> provide enough physical space for the logical TDVPS structure.
>
> Also, we have a new structure, Trust Domain Control Structure (TDCS) is the
> main control structure of a guest TD, and encrypted (using the guest TD's
> ephemeral private key).  At a high level, TDCS holds information for
> controlling TD operation as a whole, execution, EPTP, MSR bitmaps, etc. KVM
> needs to set it up.  Note that MSR bitmaps are held as part of TDCS (unlike
> VMX) because they are meant to have the same value for all VCPUs of the
> same TD.  TDCS is a multi-page logical structure composed of multiple Trust
> Domain Control Extension (TDCX) physical pages.  Trust Domain Root (TDR) is
> the root control structure of a guest TD and is encrypted using the TDX
> global private key. It holds a minimal set of state variables that enable
> guest TD control even during times when the TD's private key is not known,
> or when the TD's key management state does not permit access to memory
> encrypted using the TD's private key.
>
> The following shows the relationship between those structures.
>
>          TDR--> TDCS                     per-TD
>           |       \--> TDCX
>           \
>            \--> TDVPS                    per-TD VCPU
>                   \--> TDVPR and TDVPX
>
> The existing global struct kvm_x86_ops already defines an interface which
> fits with TDX.  But kvm_x86_ops is system-wide, not per-VM structure.  To
> allow VMX to coexist with TDs, the kvm_x86_ops callbacks will have wrappers
> "if (tdx) tdx_op() else vmx_op()" to switch VMX or TDX at run time.
>
> To split the runtime switch, the VMX implementation, and the TDX
> implementation, add main.c, and move out the vmx_x86_ops hooks in
> preparation for adding TDX, which can coexist with VMX, i.e. KVM can run
> both VMs and TDs.  Use 'vt' for the naming scheme as a nod to VT-x and as a
> concatenation of VmxTdx.
>
> The current code looks as follows.
> In vmx.c
>    static vmx_op() { ... }
>    static struct kvm_x86_ops vmx_x86_ops = {
>          .op = vmx_op,
>    initialization code
>
> The eventually converted code will look like
> In vmx.c, keep the VMX operations.
>    vmx_op() { ... }
>    VMX initialization
> In tdx.c, define the TDX operations.
>    tdx_op() { ... }
>    TDX initialization
> In x86_ops.h, declare the VMX and TDX operations.
>    vmx_op();
>    tdx_op();
> In main.c, define common wrappers for VMX and VMX.

LGTM.
One typo here, VMX and TDX.


>    static vt_ops() { if (tdx) tdx_ops() else vmx_ops() }
>    static struct kvm_x86_ops vt_x86_ops = {
>          .op = vt_op,
>    initialization to call VMX and TDX initialization
>
> Opportunistically, fix the name inconsistency from vmx_create_vcpu() and
> vmx_free_vcpu() to vmx_vcpu_create() and vxm_vcpu_free().
>
> Co-developed-by: Xiaoyao Li <xiaoyao.li@...el.com>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>