Re: [edk2] KVM: MTRR: fix memory type handling if MTRR is completely disabled

[Laszlo Ersek <lersek@redhat.com>]

Hi,

On 10/20/15 19:27, Janusz wrote:
> W dniu 15.10.2015 o 20:46, Laszlo Ersek pisze:
>> On 10/15/15 18:53, Kinney, Michael D wrote:
>>> Laszlo,
>>>
>>> There is already a PCD for this timeout that is used by CpuMpPei.
>>>
>>> 	gUefiCpuPkgTokenSpaceGuid.PcdCpuApInitTimeOutInMicroSeconds
>>>
>>> I noticed that CpuDxe is using a hard coded AP timeout.  I think we should just use this same PCD for both the PEI and DXE CPU module and then set it for OVMF to the compatible value.
>> Perfect, thank you!
>>
>> (I notice the default in the DEC file is 50000, which is half of what
>> the DXE driver hardcodes.)
>>
>> Now we only need a recommended (or experimental) value for it, and an
>> explanation why 100*1000 is no longer sufficient on KVM :)
>>
>> Thanks!
>> Laszlo
>>
>>
>>
> Laszlo,
> 
> I saw that there is already some change in ovmf for MicroSecondDelay
> https://github.com/tianocore/edk2/commit/1e410eadd80c328e66868263b3006a274ce81ae0
> Is that a fix for it? Because I tried it and it still doesn't work for
> me: https://bpaste.net/show/2514b51bf41f
> I still get internal error

I think you guys are now "mature enough OVMF users" to start employing
the correct terminology.

"edk2" (also spelled as "EDK II") is: "a modern, feature-rich,
cross-platform firmware development environment for the UEFI and PI
specifications".

The source tree contains a whole bunch of modules (drivers,
applications, libraries), organized into packages.

"OVMF" usually denotes a firmware binary built from one of the
OvmfPkg/OvmfPkg*.dsc "platform description files". Think of them as "top
level makefiles". The difference between them is the target architecture
(there's Ia32, X64, and Ia32X64 -- the last one means that the SEC and
PEI phases are 32-bit, whereas the DXE and later phases are 64-bit.) In
practice you'll only care about full X64.

Now, each of OvmfPkg/OvmfPkg*.dsc builds the following three kinds of
modules into the final binary:
- platform-independent modules from various top-level packages
- platform- (ie. Ia32/X64-) dependent modules from various top-level
  packages
- modules from under OvmfPkg that are specific to QEMU/KVM (and Xen, if
  you happen to use OVMF with Xen)

Now, when you reference a commit like 1e410ead above, you can look at
the diffstat, and decide if it is OvmfPkg-specific (third category
above) or not. Here you see UefiCpuPkg, which happens to be the second
category.

The important point is: please do *not* call any and all edk2 patches
"OVMF changes", indiscriminately. That's super confusing for people who
understand the above distinctions. Which now you do too. :)

Let me add that in edk2, patches that straddle top level packages are
generally forbidden -- you can't have a patch that modifies OvmfPkg and
UefiCpuPkg at the same time, modulo *very* rare exceptions. If a feature
or bugfix needs to touch several top-level packages, the series must be
built up carefully in stages.

Knowing all of the above, you can tell that the patch you referenced had
only *enabled* OvmfPkg to customize UefiCpuPkg, via
"PcdCpuApInitTimeOutInMicroSeconds". But for that customization to occur
actually, a small patch for OvmfPkg will be necessary too, in order to
set "PcdCpuApInitTimeOutInMicroSeconds" differently from the default.

I plan to send that patch soon. If you'd like to be CC'd, that's great
(reporting back with a Tested-by is even better!), but I'll need your
real name for that. (Or any name that looks like a real name.)

Thanks!
Laszlo