diff --git a/UefiCpuPkg/Library/MtrrLib/MtrrLib.c b/UefiCpuPkg/Library/MtrrLib/MtrrLib.c index a7adbafae3..2fd1d0153e 100644 --- a/UefiCpuPkg/Library/MtrrLib/MtrrLib.c +++ b/UefiCpuPkg/Library/MtrrLib/MtrrLib.c @@ -449,10 +449,13 @@ MtrrGetVariableMtrrWorker ( for (Index = 0; Index < VariableMtrrCount; Index++) { if (MtrrSetting == NULL) { - VariableSettings->Mtrr[Index].Base = - AsmReadMsr64 (MSR_IA32_MTRR_PHYSBASE0 + (Index << 1)); - VariableSettings->Mtrr[Index].Mask = - AsmReadMsr64 (MSR_IA32_MTRR_PHYSMASK0 + (Index << 1)); + VariableSettings->Mtrr[Index].Mask = AsmReadMsr64 (MSR_IA32_MTRR_PHYSMASK0 + (Index << 1)); + // + // Skip to read the Base MSR when the Mask.V is not set. + // + if (((MSR_IA32_MTRR_PHYSMASK_REGISTER *)&VariableSettings->Mtrr[Index].Mask)->Bits.V != 0) { + VariableSettings->Mtrr[Index].Base = AsmReadMsr64 (MSR_IA32_MTRR_PHYSBASE0 + (Index << 1)); + } } else { VariableSettings->Mtrr[Index].Base = MtrrSetting->Variables.Mtrr[Index].Base; VariableSettings->Mtrr[Index].Mask = MtrrSetting->Variables.Mtrr[Index].Mask; @@ -2540,14 +2543,14 @@ MtrrSetVariableMtrrWorker ( ASSERT (VariableMtrrCount <= ARRAY_SIZE (VariableSettings->Mtrr)); for (Index = 0; Index < VariableMtrrCount; Index++) { - AsmWriteMsr64 ( - MSR_IA32_MTRR_PHYSBASE0 + (Index << 1), - VariableSettings->Mtrr[Index].Base - ); - AsmWriteMsr64 ( - MSR_IA32_MTRR_PHYSMASK0 + (Index << 1), - VariableSettings->Mtrr[Index].Mask - ); + // + // Mask MSR is always updated since caller might need to invalidate the MSR pair. + // Base MSR is skipped when Mask.V is not set. + // + AsmWriteMsr64 (MSR_IA32_MTRR_PHYSMASK0 + (Index << 1), VariableSettings->Mtrr[Index].Mask); + if (((MSR_IA32_MTRR_PHYSMASK_REGISTER *)&VariableSettings->Mtrr[Index].Mask)->Bits.V != 0) { + AsmWriteMsr64 (MSR_IA32_MTRR_PHYSBASE0 + (Index << 1), VariableSettings->Mtrr[Index].Base); + } } } @@ -2800,7 +2803,7 @@ MtrrDebugPrintAllMtrrsWorker ( } for (Index = 0; Index < ARRAY_SIZE (Mtrrs->Variables.Mtrr); Index++) { - if ((Mtrrs->Variables.Mtrr[Index].Mask & BIT11) == 0) { + if (((MSR_IA32_MTRR_PHYSMASK_REGISTER *)&Mtrrs->Variables.Mtrr[Index].Mask)->Bits.V == 0) { // // If mask is not valid, then do not display range //