On August 23, 2022 9:07 PM, Lendacky,Thomas wrote: > 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/Platfor > >> m > >>> 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. > One of the situation of CcProbe used is in BaseIoLib. https://github.com/tianocore/edk2/blob/master/MdePkg/Library/BaseIoLibIntrinsic/IoLibInternalTdx.c#L35-L40
BaseIoLib is a basic library and it may be called by APs. While dynamic PCD access is not allowed in APs. Of course we can cache the PCD in a variable but I think it is still not safe. Reserving the OVMF work area as RT_DATA breaks the original intention of the design. Then how about this solution? https://edk2.groups.io/g/devel/message/91132 We can design 2 instances of CcProbe. One is to read the OvmfWorkArea. The other is to call Cc guest specific way to determine the type. Thanks Min -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#92795): https://edk2.groups.io/g/devel/message/92795 Mute This Topic: https://groups.io/mt/93173995/21656 Group Owner: devel+ow...@edk2.groups.io Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com] -=-=-=-=-=-=-=-=-=-=-=-
