Re: [edk2-devel] [PATCH v2 4/5] OvmfPkg/ResetVector: add 5-level paging support

["Gerd Hoffmann" <kraxel@redhat.com>]

  Hi,

> Because of these CPUID instructions, this won't work for SEV-ES / SEV-SNP.
> To use these we'll need to have a (special 32-bit) #VC handler in place.
> Currently that is done in only in OvmfPkg/ResetVector/Ia32/AmdSev.asm for
> the CheckSevFeatures function, where the #VC handler is established at the
> beginning of the function, but it is removed when leaving the function.

Noted.  Uninstalling the exception handler later (probably just before
entering long mode) should be possible I think.

> The SEV support in general needs looking into in order to support 5-level
> paging. At the time the SEV support was developed, there wasn't a page table
> library and so there is some 4-level page table manipulation support in the
> BaseMemEncryptSevLib that really needs to be converted to use the page table
> library.

Right, I remember, and I think TDX has the same problem.

> I don't have an objection to the series, as long as PcdUse5LevelPageTable is
> not set to TRUE by default for the Ovmf packages.

The patch series does not add it to the Ovmf*.dsc files, and
MdeModulePkg/MdeModulePkg.dec declares with with default being FALSE, so
yes, it is disabled by default.

take care,
  Gerd



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