Messages in this thread | | | Date | Wed, 31 Aug 2022 11:40:24 +0800 | Subject | Re: [PATCH v8 018/103] KVM: TDX: Stub in tdx.h with structs, accessors, and VMCS helpers | From | Xiaoyao Li <> |
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On 8/26/2022 12:48 PM, Isaku Yamahata wrote: > On Tue, Aug 23, 2022 at 03:40:40PM +0000, > Sean Christopherson <seanjc@google.com> 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. I've updated it as follows to use symbolic value. > > #define VMCS_ENC_ACCESS_TYPE_MASK 0x1UL > #define VMCS_ENC_ACCESS_TYPE_FULL 0x0UL > #define VMCS_ENC_ACCESS_TYPE_HIGH 0x1UL > #define VMCS_ENC_ACCESS_TYPE(field) ((field) & VMCS_ENC_ACCESS_TYPE_MASK) > > /* TDX is 64bit only. HIGH field isn't supported. */ > BUILD_BUG_ON_MSG(__builtin_constant_p(field) && > VMCS_ENC_ACCESS_TYPE(field) == VMCS_ENC_ACCESS_TYPE_HIGH, > "Read/Write to TD VMCS *_HIGH fields not supported"); > > BUILD_BUG_ON(bits != 16 && bits != 32 && bits != 64); > > #define VMCS_ENC_WIDTH_MASK GENMASK_UL(14, 13) > #define VMCS_ENC_WIDTH_16BIT (0UL << 13) > #define VMCS_ENC_WIDTH_64BIT (1UL << 13) > #define VMCS_ENC_WIDTH_32BIT (2UL << 13) > #define VMCS_ENC_WIDTH_NATURAL (3UL << 13) > #define VMCS_ENC_WIDTH(field) ((field) & VMCS_ENC_WIDTH_MASK) > > /* TDX is 64bit only. i.e. natural width = 64bit. */ > BUILD_BUG_ON_MSG(bits != 64 && __builtin_constant_p(field) && > (VMCS_ENC_WIDTH(field) == VMCS_ENC_WIDTH_64BIT || > VMCS_ENC_WIDTH(field) == VMCS_ENC_WIDTH_NATURAL), > "Invalid TD VMCS access for 64-bit field"); > BUILD_BUG_ON_MSG(bits != 32 && __builtin_constant_p(field) && > VMCS_ENC_WIDTH(field) == VMCS_ENC_WIDTH_32BIT, > "Invalid TD VMCS access for 32-bit field"); > BUILD_BUG_ON_MSG(bits != 16 && __builtin_constant_p(field) && > VMCS_ENC_WIDTH(field) == VMCS_ENC_WIDTH_16BIT, > "Invalid TD VMCS access for 16-bit field");
Actually, the original code is written by me that is copied from vmcs_check{16/32/64/l} in arch/x86/kvm/vmx/vmx_ops.h
If you are going to do above change, you'd better cook a patch to change it for vmx_ops.h at first and see opinion from community.
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