linux-kernel - Re: [PATCH 10/25] KVM: TDX: Initialize KVM supported capabilities when module setup

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Message-ID: <aa764aad-1736-459f-896e-4f43bfe8b18d@intel.com>
Date: Thu, 5 Sep 2024 21:36:17 +0800
From: Xiaoyao Li <xiaoyao.li@...el.com>
To: Nikolay Borisov <nik.borisov@...e.com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>, seanjc@...gle.com,
 pbonzini@...hat.com, kvm@...r.kernel.org
Cc: kai.huang@...el.com, isaku.yamahata@...il.com,
 tony.lindgren@...ux.intel.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/25] KVM: TDX: Initialize KVM supported capabilities
 when module setup

On 9/4/2024 7:58 PM, Nikolay Borisov wrote:
> 
> 
> On 13.08.24 г. 1:48 ч., Rick Edgecombe wrote:
>> From: Xiaoyao Li <xiaoyao.li@...el.com>
>>
>> While TDX module reports a set of capabilities/features that it
>> supports, what KVM currently supports might be a subset of them.
>> E.g., DEBUG and PERFMON are supported by TDX module but currently not
>> supported by KVM.
>>
>> Introduce a new struct kvm_tdx_caps to store KVM's capabilities of TDX.
>> supported_attrs and suppported_xfam are validated against fixed0/1
>> values enumerated by TDX module. Configurable CPUID bits derive from TDX
>> module plus applying KVM's capabilities (KVM_GET_SUPPORTED_CPUID),
>> i.e., mask off the bits that are configurable in the view of TDX module
>> but not supported by KVM yet.
>>
>> KVM_TDX_CPUID_NO_SUBLEAF is the concept from TDX module, switch it to 0
>> and use KVM_CPUID_FLAG_SIGNIFCANT_INDEX, which are the concept of KVM.
>>
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
>> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
>> ---
>> uAPI breakout v1:
>>   - Change setup_kvm_tdx_caps() to use the exported 'struct tdx_sysinfo'
>>     pointer.
>>   - Change how to copy 'kvm_tdx_cpuid_config' since 'struct tdx_sysinfo'
>>     doesn't have 'kvm_tdx_cpuid_config'.
>>   - Updates for uAPI changes
>> ---
>>   arch/x86/include/uapi/asm/kvm.h |  2 -
>>   arch/x86/kvm/vmx/tdx.c          | 81 +++++++++++++++++++++++++++++++++
>>   2 files changed, 81 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/include/uapi/asm/kvm.h 
>> b/arch/x86/include/uapi/asm/kvm.h
>> index 47caf508cca7..c9eb2e2f5559 100644
>> --- a/arch/x86/include/uapi/asm/kvm.h
>> +++ b/arch/x86/include/uapi/asm/kvm.h
>> @@ -952,8 +952,6 @@ struct kvm_tdx_cmd {
>>       __u64 hw_error;
>>   };
>> -#define KVM_TDX_CPUID_NO_SUBLEAF    ((__u32)-1)
>> -
>>   struct kvm_tdx_cpuid_config {
>>       __u32 leaf;
>>       __u32 sub_leaf;
>> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
>> index 90b44ebaf864..d89973e554f6 100644
>> --- a/arch/x86/kvm/vmx/tdx.c
>> +++ b/arch/x86/kvm/vmx/tdx.c
>> @@ -31,6 +31,19 @@ static void __used tdx_guest_keyid_free(int keyid)
>>       ida_free(&tdx_guest_keyid_pool, keyid);
>>   }
>> +#define KVM_TDX_CPUID_NO_SUBLEAF    ((__u32)-1)
>> +
>> +struct kvm_tdx_caps {
>> +    u64 supported_attrs;
>> +    u64 supported_xfam;
>> +
>> +    u16 num_cpuid_config;
>> +    /* This must the last member. */
>> +    DECLARE_FLEX_ARRAY(struct kvm_tdx_cpuid_config, cpuid_configs);
>> +};
>> +
>> +static struct kvm_tdx_caps *kvm_tdx_caps;
>> +
>>   static int tdx_get_capabilities(struct kvm_tdx_cmd *cmd)
>>   {
>>       const struct tdx_sysinfo_td_conf *td_conf = &tdx_sysinfo->td_conf;
>> @@ -131,6 +144,68 @@ int tdx_vm_ioctl(struct kvm *kvm, void __user *argp)
>>       return r;
>>   }
>> +#define KVM_SUPPORTED_TD_ATTRS (TDX_TD_ATTR_SEPT_VE_DISABLE)
> 
> Why isn't TDX_TD_ATTR_DEBUG added as well?

Because so far KVM doesn't support all the features of a DEBUG TD for 
userspace. e.g., KVM doesn't provide interface for userspace to 
read/write private memory of DEBUG TD.

> <snip>