Rafael J. Wysocki wrote:
Well, "AMD64 Architecture Programmer’s Manual" says the following:
The choice of 2 Mbyte or 4 Mbyte as the large physical-page size
depends on the value of CR4.PSE and CR4.PAE, as follows:
- If physical-address extensions are enabled (CR4.PAE=1), the
large physical-page size is 2 Mbytes, regardless of the value
of CR4.PSE.
- If physical-address extensions are disabled (CR4.PAE=0)
and CR4.PSE=1, the large physical-page size is 4 Mbytes.
- If both CR4.PAE=0 and CR4.PSE=0, the only available page
size is 4 Kbytes.
That would be a retroactive redef on the part of AMD; it probably makes
sense for x86-64 if someone thinks that is may drop support for 4 MB
pages at some point in the distant future. Still, I'm not sure Intel
would agree with the definition as stated, although I haven't looked in
the docs.
This is all extremely theoretical, since there has never been a chip
with PAE=1 and PSE=0, and I wouldn't expect one to appear any time soon.
-hpa
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