Re: [PATCH] UefiCpuPkg/LocalApicLib: Exclude second SendIpi sequence on AMD processors.

[Laszlo Ersek <lersek@redhat.com>]

Hello Leo,

On 06/13/18 22:11, Leo Duran wrote:
> On AMD processors the second SendIpi in the SendInitSipiSipi and
> SendInitSipiSipiAllExcludingSelf routines is not required, and may cause
> undesired side-effects during MP initialization.
> 
> This patch leverages the StandardSignatureIsAuthenticAMD check to exclude
> the second SendIpi and its associated MicroSecondDelay (200).

QEMU and KVM emulate some AMD processors too; of particular interest is
the recent EPYC addition, I believe (for SME/SEV, minimally).

Did you check whether the StandardSignatureIsAuthenticAMD() check
applies to those QEMU VCPU models, and if so, whether omitting the
second Startup IPI interferes with *V*CPU startup in OVMF guests? (In
multiprocessing modules, such as CpuMpPei, CpuDxe, and PiSmmCpuDxeSmm.)

Adding Brijesh, Paolo and Igor.

Thanks!
Laszlo

> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Leo Duran <leo.duran@amd.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Jeff Fan <jeff.fan@intel.com>
> Cc: Liming Gao <liming.gao@intel.com>
> ---
>  UefiCpuPkg/Library/BaseXApicLib/BaseXApicLib.c             | 12 ++++++++----
>  UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c | 12 ++++++++----
>  2 files changed, 16 insertions(+), 8 deletions(-)
> 
> diff --git a/UefiCpuPkg/Library/BaseXApicLib/BaseXApicLib.c b/UefiCpuPkg/Library/BaseXApicLib/BaseXApicLib.c
> index b0b7e32..6e80536 100644
> --- a/UefiCpuPkg/Library/BaseXApicLib/BaseXApicLib.c
> +++ b/UefiCpuPkg/Library/BaseXApicLib/BaseXApicLib.c
> @@ -554,8 +554,10 @@ SendInitSipiSipi (
>    IcrLow.Bits.DeliveryMode = LOCAL_APIC_DELIVERY_MODE_STARTUP;
>    IcrLow.Bits.Level = 1;
>    SendIpi (IcrLow.Uint32, ApicId);
> -  MicroSecondDelay (200);
> -  SendIpi (IcrLow.Uint32, ApicId);
> +  if (!StandardSignatureIsAuthenticAMD()) {
> +    MicroSecondDelay (200);
> +    SendIpi (IcrLow.Uint32, ApicId);
> +  }
>  }
>  
>  /**
> @@ -588,8 +590,10 @@ SendInitSipiSipiAllExcludingSelf (
>    IcrLow.Bits.Level = 1;
>    IcrLow.Bits.DestinationShorthand = LOCAL_APIC_DESTINATION_SHORTHAND_ALL_EXCLUDING_SELF;
>    SendIpi (IcrLow.Uint32, 0);
> -  MicroSecondDelay (200);
> -  SendIpi (IcrLow.Uint32, 0);
> +  if (!StandardSignatureIsAuthenticAMD()) {
> +    MicroSecondDelay (200);
> +    SendIpi (IcrLow.Uint32, 0);
> +  }
>  }
>  
>  /**
> diff --git a/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c b/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
> index 1f4dcf7..5d82836 100644
> --- a/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
> +++ b/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
> @@ -649,8 +649,10 @@ SendInitSipiSipi (
>    IcrLow.Bits.DeliveryMode = LOCAL_APIC_DELIVERY_MODE_STARTUP;
>    IcrLow.Bits.Level = 1;
>    SendIpi (IcrLow.Uint32, ApicId);
> -  MicroSecondDelay (200);
> -  SendIpi (IcrLow.Uint32, ApicId);
> +  if (!StandardSignatureIsAuthenticAMD()) {
> +    MicroSecondDelay (200);
> +    SendIpi (IcrLow.Uint32, ApicId);
> +  }
>  }
>  
>  /**
> @@ -683,8 +685,10 @@ SendInitSipiSipiAllExcludingSelf (
>    IcrLow.Bits.Level = 1;
>    IcrLow.Bits.DestinationShorthand = LOCAL_APIC_DESTINATION_SHORTHAND_ALL_EXCLUDING_SELF;
>    SendIpi (IcrLow.Uint32, 0);
> -  MicroSecondDelay (200);
> -  SendIpi (IcrLow.Uint32, 0);
> +  if (!StandardSignatureIsAuthenticAMD()) {
> +    MicroSecondDelay (200);
> +    SendIpi (IcrLow.Uint32, 0);
> +  }
>  }
>  
>  /**
>