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Frozen
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The XTheadMae extension is stable.
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Extension version: 1.0.
The XTheadMae ISA extension provides a way to configure memory page attributes.
These attributes are set in the page tabale entries (PTEs).
The XTheadMae extension is a non-standard non-conforming extension.
XTheadMae uses preserved [60:63] bits of the PTE, which have later been
allocted to the Svpbmt and Svnapot standard extensions.
This conflict is not on purpose, but the result of issues in the past that have been resolved since.
Therefore, the XTheadMae extension and the Svpbmt or Svnapot are in conflict.
In other words, tools should not allow to enable the XTheadMae extension and
the Svpbmt or Svnapot extensions at the same time and should report an error
if both are enabled by the user.
The table below describes the page attributes corresponding to each memory type:
| Memory type | SO | C | B |
|---|---|---|---|
Cacheable memory |
0 |
1 |
1 |
Non-cacheable memory |
0 |
0 |
1 |
Bufferable device |
1 |
0 |
1 |
Non-bufferable device |
1 |
0 |
0 |
The table below describes extend page attributes in PTE:
| Fields | Bit | Meaning |
|---|---|---|
SO |
63 |
Strong order |
C |
62 |
Cacheable |
B |
61 |
Bufferable |
T |
60 |
Trustable |
The XTheadMae extension’s availability can be probed via the
th.sxstatus.MAEE bit (bit 21).
The XTheadMae extension is available if and only if this bit is 1.
Refer to [xtheadsxstatus] for more information about the th.sxstatus CSR.