Re: [edk2-devel] [PATCH v2 3/4] OvmfPkg/PlatformPei: rewrite page table calculation

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

On 2/14/24 12:07, Gerd Hoffmann wrote:
> On Wed, Feb 14, 2024 at 11:48:57AM +0100, Laszlo Ersek wrote:
>> On 2/14/24 10:32, Gerd Hoffmann wrote:
>>>   Hi,
>>>
>>>> (3) I'm slightly disturbed by the fact that here we don't shift the
>>>> original MaxAddr by 48 bits, but Level3Pages by 9 bits. Namely, if
>>>> Level3Pages was set to 1 by the MAX (i.e., because the >> 39 resulted
>>>> in zero), then the input of *this* bit shift is nonsensical. It's a
>>>> happenstance that 1 >> 9 is zero too, for Level4Pages, and we're just
>>>> exploiting that practical result here.
>>>
>>> I had it that way initially.  Got failures for 32-bit builds in CI,
>>> because the compiler used 64-bit math intrinsics somewhere.
>>
>> Right, I had certainly expected that in advance. You must have missed my
>> earlier update on that, still in the v1 thread. My original proposal
>> there was indeed problematic in that sense, but a few minutes later I
>> posted an update, replacing the bit-shifts inside the MAX() macro
>> invocations with RShiftU64() calls:
> 
> Happened even with the RShiftU64() calls, must have been something else.

Huh! That's really strange! Thanks for trying it out!

Laszlo



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