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Message-ID: <cc443335-442d-4ed0-aa01-a6bf5c27b39c@intel.com>
Date: Fri, 20 Jun 2025 09:20:55 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
kvm@...r.kernel.org, seanjc@...gle.com
Cc: rick.p.edgecombe@...el.com, kai.huang@...el.com, adrian.hunter@...el.com,
reinette.chatre@...el.com, tony.lindgren@...el.com,
isaku.yamahata@...el.com, yan.y.zhao@...el.com,
mikko.ylinen@...ux.intel.com, kirill.shutemov@...el.com,
jiewen.yao@...el.com, binbin.wu@...ux.intel.com
Subject: Re: [PATCH 3/3] KVM: TDX: Exit to userspace for GetTdVmCallInfo
On 6/20/2025 2:01 AM, Paolo Bonzini wrote:
> From: Binbin Wu <binbin.wu@...ux.intel.com>
>
> Exit to userspace for TDG.VP.VMCALL<GetTdVmCallInfo> via KVM_EXIT_TDX,
> to allow userspace to provide information about the support of
> TDVMCALLs when r12 is 1 for the TDVMCALLs beyond the GHCI base API.
>
> GHCI spec defines the GHCI base TDVMCALLs: <GetTdVmCallInfo>, <MapGPA>,
> <ReportFatalError>, <Instruction.CPUID>, <#VE.RequestMMIO>,
> <Instruction.HLT>, <Instruction.IO>, <Instruction.RDMSR> and
> <Instruction.WRMSR>. They must be supported by VMM to support TDX guests.
>
> For GetTdVmCallInfo
> - When leaf (r12) to enumerate TDVMCALL functionality is set to 0,
> successful execution indicates all GHCI base TDVMCALLs listed above are
> supported.
>
> Update the KVM TDX document with the set of the GHCI base APIs.
>
> - When leaf (r12) to enumerate TDVMCALL functionality is set to 1, it
> indicates the TDX guest is querying the supported TDVMCALLs beyond
> the GHCI base TDVMCALLs.
> Exit to userspace to let userspace set the TDVMCALL sub-function bit(s)
> accordingly to the leaf outputs. KVM could set the TDVMCALL bit(s)
> supported by itself when the TDVMCALLs don't need support from userspace
> after returning from userspace and before entering guest. Currently, no
> such TDVMCALLs implemented, KVM just sets the values returned from
> userspace.
>
> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Binbin Wu <binbin.wu@...ux.intel.com>
> [Adjust userspace API. - Paolo]
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
> Documentation/virt/kvm/api.rst | 15 +++++++++++++-
> arch/x86/kvm/vmx/tdx.c | 38 ++++++++++++++++++++++++++++++----
> include/uapi/linux/kvm.h | 5 +++++
> 3 files changed, 53 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 3643d853a634..2b1656907356 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -7190,6 +7190,11 @@ The valid value for 'flags' is:
> u64 gpa;
> u64 size;
> } get_quote;
> + struct {
> + u64 ret;
> + u64 leaf;
> + u64 r11, r12, r13, r14;
> + } get_tdvmcall_info;
> };
> } tdx;
>
> @@ -7216,9 +7221,17 @@ queued successfully, the TDX guest can poll the status field in the
> shared-memory area to check whether the Quote generation is completed or
> not. When completed, the generated Quote is returned via the same buffer.
>
> +* ``TDVMCALL_GET_TD_VM_CALL_INFO``: the guest has requested the support
> +status of TDVMCALLs. The output values for the given leaf should be
> +placed in fields from ``r11`` to ``r14`` of the ``get_tdvmcall_info``
> +field of the union. This TDVMCALL must succeed, therefore KVM leaves
> +``ret`` equal to ``TDVMCALL_STATUS_SUCCESS`` and ``r11`` to ``r14``
> +equal to zero on entry.
> +
> KVM may add support for more values in the future that may cause a userspace
> exit, even without calls to ``KVM_ENABLE_CAP`` or similar. In this case,
> -it will enter with output fields already valid; in the common case, the
> +it will enter with output fields already valid as mentioned for
> +``TDVMCALL_GET_TD_VM_CALL_INFO`` above; in the common case, the
> ``unknown.ret`` field of the union will be ``TDVMCALL_STATUS_SUBFUNC_UNSUPPORTED``.
> Userspace need not do anything if it does not wish to support a TDVMCALL.
> ::
> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 6878a76069f8..5804d1b1ea0e 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1451,18 +1451,49 @@ static int tdx_emulate_mmio(struct kvm_vcpu *vcpu)
> return 1;
> }
>
> +static int tdx_complete_get_td_vm_call_info(struct kvm_vcpu *vcpu)
> +{
> + struct vcpu_tdx *tdx = to_tdx(vcpu);
> +
> + tdvmcall_set_return_code(vcpu, vcpu->run->tdx.get_tdvmcall_info.ret);
> +
> + /*
> + * For now, there is no TDVMCALL beyond GHCI base API supported by KVM
> + * directly without the support from userspace, just set the value
> + * returned from userspace.
> + */
> + tdx->vp_enter_args.r11 = vcpu->run->tdx.get_tdvmcall_info.r11;
> + tdx->vp_enter_args.r12 = vcpu->run->tdx.get_tdvmcall_info.r12;
> + tdx->vp_enter_args.r13 = vcpu->run->tdx.get_tdvmcall_info.r13;
> + tdx->vp_enter_args.r14 = vcpu->run->tdx.get_tdvmcall_info.r14;
> +
> + return 1;
> +}
> +
> static int tdx_get_td_vm_call_info(struct kvm_vcpu *vcpu)
> {
> struct vcpu_tdx *tdx = to_tdx(vcpu);
>
> - if (tdx->vp_enter_args.r12)
> - tdvmcall_set_return_code(vcpu, TDVMCALL_STATUS_INVALID_OPERAND);
> - else {
> + switch (tdx->vp_enter_args.r12) {
> + case 1:
> + vcpu->run->tdx.get_tdvmcall_info.leaf = tdx->vp_enter_args.r12;
> + vcpu->run->exit_reason = KVM_EXIT_TDX;
> + vcpu->run->tdx.flags = 0;
> + vcpu->run->tdx.nr = TDVMCALL_GET_TD_VM_CALL_INFO;
> + vcpu->run->tdx.get_tdvmcall_info.ret = TDVMCALL_STATUS_SUCCESS;
> + vcpu->run->tdx.get_tdvmcall_info.r11 = 0;
> + vcpu->run->tdx.get_tdvmcall_info.r12 = 0;
> + vcpu->run->tdx.get_tdvmcall_info.r13 = 0;
> + vcpu->run->tdx.get_tdvmcall_info.r14 = 0;
> + vcpu->arch.complete_userspace_io = tdx_complete_get_td_vm_call_info;
> + return 0;
> + default:
> tdx->vp_enter_args.r11 = 0;
> + tdx->vp_enter_args.r12 = 0;
> tdx->vp_enter_args.r13 = 0;
> tdx->vp_enter_args.r14 = 0;
> + return 1;
Though it looks OK to return all-0 for r12 == 0 and undefined case of
r12 > 1, I prefer returning TDVMCALL_STATUS_INVALID_OPERAND for
undefined case.
So please make above "case 0:", and make the "default:" return
TDVMCALL_STATUS_INVALID_OPERAND
> }
> - return 1;
> }
>
> static int tdx_complete_simple(struct kvm_vcpu *vcpu)
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 6708bc88ae69..fb3b4cd8d662 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -461,6 +461,11 @@ struct kvm_run {
> __u64 gpa;
> __u64 size;
> } get_quote;
> + struct {
> + __u64 ret;
> + __u64 leaf;
> + __u64 r11, r12, r13, r14;
> + } get_tdvmcall_info;
> };
> } tdx;
> /* Fix the size of the union. */
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