Re: [Patch] MdeModulePkg DxeCore: Fix for missing MAT update


Liming Gao
 

Laszlo:

-----Original Message-----
From: Laszlo Ersek [mailto:lersek@redhat.com]
Sent: Saturday, August 17, 2019 2:54 AM
To: Gao, Liming <liming.gao@intel.com>; devel@edk2.groups.io; Kinney,
Michael D <michael.d.kinney@intel.com>
Cc: Mike Turner <miketur@microsoft.com>; Wang, Jian J
<jian.j.wang@intel.com>; Wu, Hao A <hao.a.wu@intel.com>; Bi, Dandan
<dandan.bi@intel.com>
Subject: Re: [edk2-devel] [Patch] MdeModulePkg DxeCore: Fix for missing
MAT update

On 08/16/19 17:24, Gao, Liming wrote:
Laszlo:

-----Original Message-----
From: devel@edk2.groups.io [mailto:devel@edk2.groups.io] On Behalf Of
Laszlo Ersek
Sent: Friday, August 16, 2019 11:18 PM
To: Gao, Liming <liming.gao@intel.com>; devel@edk2.groups.io; Kinney,
Michael D <michael.d.kinney@intel.com>
Cc: Mike Turner <miketur@microsoft.com>; Wang, Jian J
<jian.j.wang@intel.com>; Wu, Hao A <hao.a.wu@intel.com>; Bi, Dandan
<dandan.bi@intel.com>
Subject: Re: [edk2-devel] [Patch] MdeModulePkg DxeCore: Fix for
missing MAT update

On 08/14/19 17:55, Gao, Liming wrote:

If Platform PEIM doesn't build HOB, DxeIpl will not build HOB,
My reading of the code is the opposite. If the platform PEIM does not
build the HOB, then the DXE IPL PEIM will attempt to build the HOB,
from the UEFI variable.

At commit caa7d3a896f6, in file
"MdeModulePkg/Core/DxeIplPeim/DxeLoad.c", function DxeLoadCore(),
we
have:

363 if (GetFirstGuidHob ((CONST EFI_GUID
*)&gEfiMemoryTypeInformationGuid) == NULL) {
364 //
365 // Don't build GuidHob if GuidHob has been installed.
366 //
367 Status = PeiServicesLocatePpi (
368 &gEfiPeiReadOnlyVariable2PpiGuid,
369 0,
370 NULL,
371 (VOID **)&Variable
372 );
373 if (!EFI_ERROR (Status)) {
374 DataSize = sizeof (MemoryData);
375 Status = Variable->GetVariable (
376 Variable,
377 EFI_MEMORY_TYPE_INFORMATION_VARIABLE_NAME,
378 &gEfiMemoryTypeInformationGuid,
379 NULL,
380 &DataSize,
381 &MemoryData
382 );
383 if (!EFI_ERROR (Status) &&
ValidateMemoryTypeInfoVariable(MemoryData, DataSize)) {

Only when this variable exists, Hob will be built. But, if no PEIM
builds Hob, BDS will not set the variable.
So, there is still no HOB.
So how is a platform supposed to enable this feature?

If PlatformPei never builds the HOB, the variable will never be created,
so the DXE IPL PEIM will also not build the HOB, ever.

If PlatformPei builds the HOB with static data, then BDS will set
(update) the variable, yes, but the DXE IPL PEIM will ignore the
variable, because PlatformPei already built the HOB.

So... Is PlatformPei supposed to use the Variable PPI, check if the
variable exists, and create the static HOB only if the variable is
absent?

... Ugh, wait. I've actually implemented this for OVMF almost 2 years
ago! And the answer to my question is "yes":

https://bugzilla.tianocore.org/show_bug.cgi?id=386
https://lists.01.org/pipermail/edk2-devel/2017-November/018312.html

See the OnReadOnlyVariable2Available() function:

+ //
+ // Check if the "MemoryTypeInformation" variable exists, in the
+ // gEfiMemoryTypeInformationGuid namespace.
+ //
+ ReadOnlyVariable2 = Ppi;
+ DataSize = 0;
+ Status = ReadOnlyVariable2->GetVariable (
+ ReadOnlyVariable2,
+ EFI_MEMORY_TYPE_INFORMATION_VARIABLE_NAME,
+ &gEfiMemoryTypeInformationGuid,
+ NULL,
+ &DataSize,
+ NULL
+ );
+ if (Status == EFI_BUFFER_TOO_SMALL) {
+ //
+ // The variable exists; the DXE IPL PEIM will build the HOB from it.
+ //
+ return EFI_SUCCESS;
+ }
+ //
+ // Install the default memory type information HOB.
+ //
+ BuildMemTypeInfoHob ();

Apologies for forgetting about this; you are right.

Too bad my work for TianoCore#386 was rejected. :(
So, this is one value to add PEI variable support in OVMF.
Do you consider to approve this feature request?

Thanks
Liming

Thanks
Laszlo

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