Re: [PATCH 1/1] OvmfPkg: Reserve the Ovmf work area as RT_DATA

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

On 8/23/22 03:40, Xu, Min M wrote:
> On August 23, 2022 3:38 PM, Gerd Hoffmann wrote:
>>    Hi,
>>
>>> Ah, I forget to reserve the work-area as RT_Data in below code:
>>>        BuildMemoryAllocationHob (
>>>          (EFI_PHYSICAL_ADDRESS)(UINTN)FixedPcdGet32
>> (PcdOvmfWorkAreaBase),
>>>          (UINT64)(UINTN)FixedPcdGet32 (PcdOvmfWorkAreaSize),
>>>          PlatformInfoHob->S3Supported ? EfiACPIMemoryNVS :
>> EfiRuntimeServicesData  <-- ACPI_NVS is not accessible either in OS-Runtime.
>>>          );
>>>
>> https://github.com/tianocore/edk2/blob/master/OvmfPkg/Library/Platform
>>> InitLib/MemDetect.c#L1022-L1026
>>
>> With that changed to use EfiRuntimeServicesData unconditionally the page
>> fault is gone.
>>
>>> Gerd, do you think we can reserve Ovmf WorkArea as RT_Data even when
>> S3 is supported?
>>
>> Hmm, not fully sure how the various memory types are handled when the
>> VM is suspended.
>>
> Tom suggested that the work area should not  be kept around. In stead a PCD should be used.
> https://edk2.groups.io/g/devel/message/92617
> 
> But the dynamic PCD is not thread-safe and it cannot be accessed by APs.
> 
> Now we have 2 solutions to fix this issue.
> 1. Reserve the Ovmf work area as RT_DATA.
> 2. Split the CcProbeLib into 2 instances. See https://edk2.groups.io/g/devel/message/91132
> 
> Gerd & Tom, what's your thought?

Runtime service call are restricted so that you don't have concurrent 
threads executing (see section 8.1 of the specification). Without that you 
would have problems with runtime services today.

Thanks,
Tom

> 
> Thanks
> Min
>