[edk2-devel] [RFC PATCH 05/28] OvmfPkg: Create GHCB pages for use during Pei and Dxe phase

[Laszlo Ersek]

On 08/21/19 23:42, Lendacky, Thomas wrote:
> On 8/21/19 9:31 AM, Laszlo Ersek wrote:
>> On 08/19/19 23:35, Lendacky, Thomas wrote:
>>> From: Tom Lendacky <thomas.lendacky at amd.com>
>>>
>>> Allocate memory for the GHCB pages during SEV initialization for use
>>> during Pei and Dxe phases. Since the GHCB pages must be mapped as shared
>>> pages, modify CreateIdentityMappingPageTables() so that pagetable entries
>>> are created without the encryption bit set.
>>>
>>> Signed-off-by: Tom Lendacky <thomas.lendacky at amd.com>
>>> ---
>>>  UefiCpuPkg/UefiCpuPkg.dec                     |  4 ++
>>>  OvmfPkg/OvmfPkgX64.dsc                        |  4 ++
>>>  MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf       |  3 +
>>>  OvmfPkg/PlatformPei/PlatformPei.inf           |  2 +
>>>  .../Core/DxeIplPeim/X64/VirtualMemory.h       | 12 +++-
>>>  .../Core/DxeIplPeim/Ia32/DxeLoadFunc.c        |  4 +-
>>>  .../Core/DxeIplPeim/X64/DxeLoadFunc.c         | 11 +++-
>>>  .../Core/DxeIplPeim/X64/VirtualMemory.c       | 49 ++++++++++----
>>>  .../MemEncryptSevLibInternal.c                |  1 -
>>>  .../BaseMemEncryptSevLib/X64/VirtualMemory.c  | 33 ++++++++--
>>>  OvmfPkg/PlatformPei/AmdSev.c                  | 64 +++++++++++++++++++
>>>  11 files changed, 164 insertions(+), 23 deletions(-)
>>
>> Should be split to at least four patches (UefiCpuPkg, MdeModulePkg,
>> OvmfPkg/BaseMemEncryptSevLib, OvmfPkg/PlatformPei).
>>
>> In addition, MdeModulePkg content must not depend on UefiCpuPkg content
>> -- if modules under both packages need to consume a new PCD, then the
>> PCD should be declared under MdeModulePkg. The rough dependency order is:
>>
>> - MdePkg (must be self-contained)
>> - MdeModulePkg (may consume MdePkg)
>> - UefiCpuPkg (may consume everything above, to my knowledge)
>> - OvmfPkg (may consume everything above)
>>
> 
> Ok, thanks for the guidance.
> 
> Ideally, I just would like to modify the newly created page tables after
> the call to CreateIdentityMappingPageTables() in MdeModulePkg/Core/
> DxeIplPeim/Ia32/DxeLoadFunc.c. Is there a preferred way to add a listener
> or callback or notification service so that the main changes would be
> limited to the OvmfPkg files and would that be acceptable?

* https://bugzilla.tianocore.org/show_bug.cgi?id=623

  Reported on 2017-07-07, resolved as WONTFIX on 2019-07-30 ("no
  resources").

  And it's not like patches had not been proposed -- Leo had implemented
  a notification service --; they were rejected.

* https://bugzilla.tianocore.org/show_bug.cgi?id=847

  Reported on 2018-01-11, marked "not high priority" as of 2019-07-23
  <https://www.mail-archive.com/devel@edk2.groups.io/msg05507.html>.

I don't know what to tell you. While nobody seems to disagree with the
necessity of such a service and/or library, core maintainers have
rejected all the code proposals thus far (= "don't do that"). And I'm
unaware of any constructive guidance (= "do this instead").

I suggest filing a Feature Request BZ for SEV-ES enablement (for
OvmfPkg), and referencing that as "dependent bug" in both of the
above-mentioned BZs. It might also help to dial in to the APAC/NAMO
design / bug triage meeting, and campaign for the feature there.

https://github.com/tianocore/tianocore.github.io/wiki/Bug-Triage

I have a bad track record at convincing core maintainers to do what they
don't want to do. And I see escalating such problems from email to phone
as a work-around, sort of "wear down your opponent by sheer
persistence". So I avoid that. But, I've seen the approach work for
others, so you might have better luck.

(The APAC/NAMO call is also at a bad time for me, in UTC+1 / UTC+2.)

I think the present RFC patches are a good way to re-raise these topics.

Laszlo

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