Messages in this thread | | | Date | Fri, 26 Aug 2022 14:24:24 +0800 | Subject | Re: [PATCH v8 018/103] KVM: TDX: Stub in tdx.h with structs, accessors, and VMCS helpers | From | Binbin Wu <> |
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On 2022/8/23 23:40, Sean Christopherson wrote: > On Tue, Aug 23, 2022, Binbin Wu wrote: >> On 2022/8/8 6:01, isaku.yamahata@intel.com wrote: >>> +static __always_inline void tdvps_vmcs_check(u32 field, u8 bits) >>> +{ >>> + BUILD_BUG_ON_MSG(__builtin_constant_p(field) && (field) & 0x1, >>> + "Read/Write to TD VMCS *_HIGH fields not supported"); >>> + >>> + BUILD_BUG_ON(bits != 16 && bits != 32 && bits != 64); >>> + >>> + BUILD_BUG_ON_MSG(bits != 64 && __builtin_constant_p(field) && >>> + (((field) & 0x6000) == 0x2000 || >>> + ((field) & 0x6000) == 0x6000), >>> + "Invalid TD VMCS access for 64-bit field"); >> if bits is 64 here, "bits != 64" is false, how could this check for "Invalid >> TD VMCS access for 64-bit field"? > Bits 14:13 of the encoding, which is extracted by "(field) & 0x6000", encodes the > width of the VMCS field. Bit 0 of the encoding, "(field) & 0x1" above, is a modifier > that is only relevant when operating in 32-bit mode, and is disallowed because TDX is > 64-bit only. > > This yields four possibilities for TDX: > > (field) & 0x6000) == 0x0000 : 16-bit field > (field) & 0x6000) == 0x2000 : 64-bit field > (field) & 0x6000) == 0x4000 : 32-bit field > (field) & 0x6000) == 0x6000 : 64-bit field (technically "natural width", but > effectively 64-bit because TDX is > 64-bit only) > > The assertion is that if the encoding indicates a 64-bit field (0x2000 or 0x6000), > then the number of bits KVM is accessing must be '64'. The below assertions do > the same thing for 32-bit and 16-bit fields.
Thanks for explanation, it is crystal clear to me now. :)
> >>> + BUILD_BUG_ON_MSG(bits != 32 && __builtin_constant_p(field) && >>> + ((field) & 0x6000) == 0x4000, >>> + "Invalid TD VMCS access for 32-bit field"); >> ditto >> >> >>> + BUILD_BUG_ON_MSG(bits != 16 && __builtin_constant_p(field) && >>> + ((field) & 0x6000) == 0x0000, >>> + "Invalid TD VMCS access for 16-bit field"); >> ditto
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