Re: [edk2-devel] [Patch V3 0/8] Create page table by CpuPageTableLib in DxeIpl

["Ard Biesheuvel" <ardb@kernel.org>]

On Mon, 24 Apr 2023 at 19:51, Kinney, Michael D
<michael.d.kinney@intel.com> wrote:
>
> Hi Ard,
>
> Thanks for the feedback.  Let's work on this approach.
>
> Are there similar needs for CPU related services in the DXE Core before
> the CPU AP is loaded?
>
> If we are going to define a new lib class to abstract DXE IPL requirements,
> it would be good to cover DXE Core requirements too.
>

Yeah, excellent point.

The problem I have had to work around in my strict permissions series
(which includes the linked patch) is that there is a window from the
moment DXE core is dispatched until the moment the CPU arch protocol
DXE driver is dispatched where we don't have an architectural means to
manipulate memory permissions.

So what we'd need here is a library version of the following method

typedef
EFI_STATUS
(EFIAPI *EFI_CPU_SET_MEMORY_ATTRIBUTES)(
  IN EFI_CPU_ARCH_PROTOCOL              *This,
  IN  EFI_PHYSICAL_ADDRESS              BaseAddress,
  IN  UINT64                            Length,
  IN  UINT64                            Attributes
  );

*However*, I am aware that the X86 DXE IPL code deviates from this, as
it needs to build long mode compatible page tables before switching
from IA32 to X64, right?
So whether that use case can be served with this prototype is
doubtful, but I guess it /would/ make sense to define a single library
abstraction that can accommodate all of these use cases.

Happy to discuss this in more detail,



>
> > -----Original Message-----
> > From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Ard Biesheuvel
> > Sent: Monday, April 24, 2023 10:24 AM
> > To: devel@edk2.groups.io; Tan, Dun <dun.tan@intel.com>
> > Subject: Re: [edk2-devel] [Patch V3 0/8] Create page table by CpuPageTableLib in DxeIpl
> >
> > On Mon, 24 Apr 2023 at 12:06, duntan <dun.tan@intel.com> wrote:
> > >
> > > In V3 patch set:
> > > 1. Add a new patch 'MdePkg: Move CpuPageTableLib defination to MdePkg' to Move CpuPageTableLib defination from UefiCpuPkg to
> > MdePkg.
> > >    So that MdeModulePkg doesn't need to depend on UefiCpuPkg.
> >
> > As I replied to the other patch, I think adding CpuPageTableLib to
> > MdePkg in its current form (even only the interface) is not the right
> > approach here. The function protoypes and enums exposed by this
> > library are highly specific to a particular implementation.
> >
> > There is a clear use case here, which is the DXE IPL code, and as has
> > been suggested in the other thread, it would be more appropriate to
> > define an abstraction regarding this use case, and define it as a
> > library class (with a NULL implementation) in MdeModulePkg. That way,
> > UefiCpuPkg can provide the x86 implementation based on
> > CpuPageTableLilb, and other architectures can do likewise.
> >
> > Please refer to the patch below, which illustrates why there are other
> > requirements in this area:
> >
> > https://edk2.groups.io/g/devel/message/101122
> >
> > --
> > Ard.
> >
> >
> >
> >
> > > 2. Modify the patch 'MdeModulePkg/DxeIpl: Create page table by CpuPageTableLib' to set GHCB page to be mapped as unencrypted
> > for each CPU for AMD SEV feature.
> > >
> > > Dun Tan (8):
> > >   MdePkg: Move CpuPageTableLib defination to MdePkg
> > >   EmulatorPkg: Add CpuPageTableLib required by DxeIpl in DSC
> > >   IntelFsp2Pkg: Add CpuPageTableLib required by DxeIpl in DSC
> > >   MdeModulePkg: Add CpuPageTableLib required by DxeIpl in DSC
> > >   OvmfPkg: Add CpuPageTableLib required by DxeIpl in DSC file
> > >   MdeModulePkg/DxeIpl: Create page table by CpuPageTableLib
> > >   MdeModulePkg/DxeIpl: Remove duplicated code to enable NX
> > >   MdeModulePkg/DxeIpl: Refinement to the code to set PageTable as RO
> > >
> > >  EmulatorPkg/EmulatorPkg.dsc                              |   3 ++-
> > >  IntelFsp2Pkg/Tools/Tests/QemuFspPkg.dsc                  |   3 ++-
> > >  MdeModulePkg/Core/DxeIplPeim/DxeIpl.h                    |   3 ++-
> > >  MdeModulePkg/Core/DxeIplPeim/DxeIpl.inf                  |   5 ++++-
> > >  MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c          | 112 ++++----------------------------------------------------------
> > --------------------------------------------------
> > >  MdeModulePkg/Core/DxeIplPeim/X64/DxeLoadFunc.c           |   5 +++--
> > >  MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.c         | 720
> > ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> > ++++++++++++++++++++++++++++++++++++++++----------------------------------------------------------------------------------------
> > --------------------------------------------------------------------------------------------------------------------------------
> > --------------------------------------------------------------------------------------------------------------------------------
> > --------------------------------------------------------------------------------------------------------------------------------
> > --------------------------------------------------------------------------------
> > >  MdeModulePkg/Core/DxeIplPeim/X64/VirtualMemory.h         | 182 ++++++++++----------------------------------------------------
> > ------------------------------------------------------------------------------------------------------------------------
> > >  MdeModulePkg/MdeModulePkg.dsc                            |   3 ++-
> > >  {UefiCpuPkg => MdePkg}/Include/Library/CpuPageTableLib.h |   0
> > >  MdePkg/MdePkg.dec                                        |   5 ++++-
> > >  OvmfPkg/AmdSev/AmdSevX64.dsc                             |   2 +-
> > >  OvmfPkg/Bhyve/BhyveX64.dsc                               |   3 ++-
> > >  OvmfPkg/CloudHv/CloudHvX64.dsc                           |   2 +-
> > >  OvmfPkg/Microvm/MicrovmX64.dsc                           |   2 +-
> > >  OvmfPkg/OvmfPkgIa32.dsc                                  |   3 ++-
> > >  OvmfPkg/OvmfPkgIa32X64.dsc                               |   2 +-
> > >  OvmfPkg/OvmfPkgX64.dsc                                   |   2 +-
> > >  OvmfPkg/OvmfXen.dsc                                      |   2 +-
> > >  UefiCpuPkg/UefiCpuPkg.dec                                |   3 ---
> > >  20 files changed, 211 insertions(+), 851 deletions(-)
> > >  rename {UefiCpuPkg => MdePkg}/Include/Library/CpuPageTableLib.h (100%)
> > >
> > > --
> > > 2.31.1.windows.1
> > >
> > >
> > >
> > >
> > >
> > >
> >
> >
> > 
> >
>