Re: [Patch v2 0/6] Add "test then write" mechanism.

["Laszlo Ersek" <lersek@redhat.com>]

On 08/12/19 12:31, Eric Dong wrote:
> V2 changes:
> 1. Split CR read/write action in to one discrete patch
> 2. Keep the old logic which continue the process if error found.
> 
> Below code is current implementation:
>   if (MsrRegister[ProcessorNumber].Bits.Lock == 0) {
>     CPU_REGISTER_TABLE_WRITE_FIELD (
>       ProcessorNumber,
>       Msr,
>       MSR_IA32_FEATURE_CONTROL,
>       MSR_IA32_FEATURE_CONTROL_REGISTER,
>       Bits.Lock,
>       1
>     );
>   }
> 
> With below steps, the Bits.Lock bit will lose its value:
> 1. Trig normal boot, the Bits.Lock is 0. 1 will be added
>    into the register table and then will set to the MSR.
> 2. Trig warm reboot, MSR value preserves. After normal boot phase,
>    the Bits.Lock is 1, so it will not be added into the register
>    table during the warm reboot phase.
> 3. Trig S3 then resume, the Bits.Lock change to 0 and Bits.Lock is
>    not added in register table during normal boot phase. so it's
>    still 0 after resume. 
> This is not an expect behavior. The expect result is the value should
> always 1 after booting or resuming from S3.
> 
> The root cause for this issue is
> 1. driver bases on current value to insert the "set value action" to
>    the register table.
> 2. Some MSRs may reserve their value during warm reboot. So the insert
>    action may be skip after warm reboot.
> 
> The solution for this issue is:
> 1. Always add "Test then Set" action for above referred MSRs.
> 2. Detect current value before set new value. Only set new value when
>    current value not same as new value.
> 
> Cc: Ray Ni <ray.ni@intel.com>
> Cc: Laszlo Ersek <lersek@redhat.com>
> 
> Eric Dong (6):
>   UefiCpuPkg/RegisterCpuFeaturesLib: Add "Test Then Write" Macros.
>   UefiCpuPkg/PiSmmCpuDxeSmm: Combine CR read/write action in one
>     function.
>   UefiCpuPkg/PiSmmCpuDxeSmm: Supports test then write new value logic.
>   UefiCpuPkg/RegisterCpuFeaturesLib: Combine CR read/write action in one
>     function.
>   UefiCpuPkg/RegisterCpuFeaturesLib: Supports test then write new value
>     logic.
>   UefiCpuPkg/CpuCommonFeaturesLib: Use new macros.
> 
>  UefiCpuPkg/Include/AcpiCpuData.h              |   1 +
>  .../Include/Library/RegisterCpuFeaturesLib.h  |  77 +++++++++-
>  .../CpuCommonFeaturesLib/CpuCommonFeatures.h  |  15 --
>  .../CpuCommonFeaturesLib.c                    |   8 +-
>  .../CpuCommonFeaturesLib/FeatureControl.c     | 141 ++++++------------
>  .../CpuCommonFeaturesLib/MachineCheck.c       |  23 ++-
>  .../CpuFeaturesInitialize.c                   | 141 ++++++++++++------
>  .../RegisterCpuFeaturesLib.c                  |  14 +-
>  UefiCpuPkg/PiSmmCpuDxeSmm/CpuS3.c             | 135 +++++++++++------
>  9 files changed, 323 insertions(+), 232 deletions(-)
> 

Please don't forget to build-test this series for IA32 too.

Thanks
Laszlo