Reviewed-by: Ray Ni <ray...@intel.com>
> -----Original Message-----
> From: Kinney, Michael D
> Sent: Thursday, April 25, 2019 10:54 AM
> To: devel@edk2.groups.io
> Cc: Dong, Eric <eric.d...@intel.com>; Ni, Ray <ray...@intel.com>; Laszlo
> Ersek <ler...@redhat.com>
> Subject: [Patch 2/4] UefiCpuPkg/MpInitLib: Avoid MSR_IA32_APIC_BASE for
> single core
>
> Avoid access to MSR_IA32_APIC_BASE that may not be supported
> on single core CPUs. If PcdCpuMaxLogicalProcessorNumber is 1,
> then there is only one CPU that must be the BSP.
>
> Cc: Eric Dong <eric.d...@intel.com>
> Cc: Ray Ni <ray...@intel.com>
> Cc: Laszlo Ersek <ler...@redhat.com>
> Signed-off-by: Michael D Kinney <michael.d.kin...@intel.com>
> ---
> UefiCpuPkg/Library/MpInitLib/PeiMpLib.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/UefiCpuPkg/Library/MpInitLib/PeiMpLib.c
> b/UefiCpuPkg/Library/MpInitLib/PeiMpLib.c
> index 35dff91fd2..5488049c08 100644
> --- a/UefiCpuPkg/Library/MpInitLib/PeiMpLib.c
> +++ b/UefiCpuPkg/Library/MpInitLib/PeiMpLib.c
> @@ -1,7 +1,7 @@
> /** @file
> MP initialize support functions for PEI phase.
>
> - Copyright (c) 2016 - 2018, Intel Corporation. All rights reserved.<BR>
> + Copyright (c) 2016 - 2019, Intel Corporation. All rights reserved.<BR>
> SPDX-License-Identifier: BSD-2-Clause-Patent
>
> **/
> @@ -101,6 +101,19 @@ GetCpuMpData (
> MSR_IA32_APIC_BASE_REGISTER ApicBaseMsr;
> IA32_DESCRIPTOR Idtr;
>
> + //
> + // If there is only 1 CPU, then it must be the BSP. This avoids an access
> to
> + // MSR_IA32_APIC_BASE that may not be supported on single core CPUs.
> + //
> + if (PcdGet32 (PcdCpuMaxLogicalProcessorNumber) == 1) {
> + CpuMpData = GetCpuMpDataFromGuidedHob ();
> + ASSERT (CpuMpData != NULL);
> + return CpuMpData;
> + }
> +
> + //
> + // Otherwise use MSR_IA32_APIC_BASE to determine if the CPU is BSP or
> AP.
> + //
> ApicBaseMsr.Uint64 = AsmReadMsr64 (MSR_IA32_APIC_BASE);
> if (ApicBaseMsr.Bits.BSP == 1) {
> CpuMpData = GetCpuMpDataFromGuidedHob ();
> --
> 2.21.0.windows.1
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