Re: [edk2-devel] [PATCH 2/3] OvmfPkg/PlatformPei: rewrite page table calculation

["Laszlo Ersek" <lersek@redhat.com>]

On 1/31/24 16:13, Laszlo Ersek wrote:

> (3) I'm sorry, these +1 additions *really* annoy me, not to mention the
> fact that we *include* those increments in the further shifting. Can we do:
> 
>   UINT64  End;
>   UINT64  Level2Pages, Level3Pages, Level4Pages, Level5Pages;
> 
>   End         = 1LLU << PlatformInfoHob->PhysMemAddressWidth;
>   Level2Pages = Page1GSupport ? 0LLU : End >> 30;
>   Level3Pages = MAX (End >> 39, 1LLU);
>   Level4Pages = MAX (End >> 48, 1LLU);
>   Level5Pages = 1;
> 
> This doesn't seem any more complicated, and it's exact, I believe.

Sorry, I forgot about an edk2 portability rule here. We shouldn't do
64-bit wide "native" shifts in code that may be compiled for 32-bit.
Instead, we're supposed to use LShiftU64() and RShiftU64(), from
BaseLib. Thus:

  UINT64  End;
  UINT64  Level2Pages, Level3Pages, Level4Pages, Level5Pages;

  End         = LShiftU64 (1, PlatformInfoHob->PhysMemAddressWidth);
  Level2Pages = Page1GSupport ? 0LLU : RShiftU64 (End, 30);
  Level3Pages = MAX (RShiftU64 (End, 39), 1LLU);
  Level4Pages = MAX (RShiftU64 (End, 48), 1LLU);
  Level5Pages = 1;

Laszlo



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