Messages in this thread | | | Date | Wed, 17 Apr 2024 10:06:03 +1200 | Subject | Re: [PATCH v19 027/130] KVM: TDX: Define TDX architectural definitions | From | "Huang, Kai" <> |
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On 17/04/2024 4:28 am, Yamahata, Isaku wrote: > On Tue, Apr 16, 2024 at 12:55:33PM +1200, > "Huang, Kai" <kai.huang@intel.com> wrote: > >> >> >> On 5/03/2024 9:21 pm, Isaku Yamahata wrote: >>> On Fri, Mar 01, 2024 at 03:25:31PM +0800, >>> Yan Zhao <yan.y.zhao@intel.com> wrote: >>> >>>>> + * TD_PARAMS is provided as an input to TDH_MNG_INIT, the size of which is 1024B. >>>>> + */ >>>>> +#define TDX_MAX_VCPUS (~(u16)0) >>>> This value will be treated as -1 in tdx_vm_init(), >>>> "kvm->max_vcpus = min(kvm->max_vcpus, TDX_MAX_VCPUS);" >>>> >>>> This will lead to kvm->max_vcpus being -1 by default. >>>> Is this by design or just an error? >>>> If it's by design, why not set kvm->max_vcpus = -1 in tdx_vm_init() directly. >>>> If an unexpected error, may below is better? >>>> >>>> #define TDX_MAX_VCPUS (int)((u16)(~0UL)) >>>> or >>>> #define TDX_MAX_VCPUS 65536 >>> >>> You're right. I'll use ((int)U16_MAX). >>> As TDX 1.5 introduced metadata MAX_VCPUS_PER_TD, I'll update to get the value >>> and trim it further. Something following. >>> >> >> [...] >> >>> + u16 max_vcpus_per_td; >>> + >> >> [...] >> >>> - kvm->max_vcpus = min(kvm->max_vcpus, TDX_MAX_VCPUS); >>> + kvm->max_vcpus = min3(kvm->max_vcpus, tdx_info->max_vcpus_per_td, >>> + TDX_MAX_VCPUS); >> >> [...] >> >>> -#define TDX_MAX_VCPUS (~(u16)0) >>> +#define TDX_MAX_VCPUS ((int)U16_MAX) >> >> Why do you even need TDX_MAX_VCPUS, given it cannot exceed U16_MAX and you >> will have the 'u16 max_vcpus_per_td' anyway? >> >> IIUC, in KVM_ENABLE_CAP(KVM_CAP_MAX_VCPUS), we can overwrite the >> kvm->max_vcpus to the 'max_vcpus' provided by the userspace, and make sure >> it doesn't exceed tdx_info->max_vcpus_per_td. >> >> Anything I am missing? > > With the latest TDX 1.5 module, we don't need TDX_MAX_VCPUS. > > The metadata MD_FIELD_ID_MAX_VCPUS_PER_TD was introduced at the middle version > of TDX 1.5. (I don't remember the exact version.), the logic was something > like as follows. Now if we fail to read the metadata, disable TDX. > > read metadata MD_FIELD_ID_MAX_VCPUS_PER_TD; > if success > tdx_info->max_vcpu_per_td = the value read metadata > else > tdx_info->max_vcpu_per_td = TDX_MAX_VCPUS; >
OK. But even the SEAMCALL can fail, we can just use U16_MAX directly when it fails given we can see clearly the type of max_vcpu_per_td is 'u16'.
if success tdx_info->max_vcpu_per_td = the value read metadata else tdx_info->max_vcpu_per_td = U16_MAX;
So I don't see why TDX_MAX_VCPUS is needed (especially in tdx_arch.h as it is not an architectural value but just some value chosen for our convenience).
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