improvements to Zcheripte text #451
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arichardson
approved these changes
Nov 13, 2024
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Agreed
…On Wed, 13 Nov 2024, 21:04 Jessica Clarke, ***@***.***> wrote:
***@***.**** commented on this pull request.
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In src/cheri-pte-ext.adoc
<#451 (comment)>:
>
-NOTE: There is no explicit mechanism for enabling or disabling {cheri_pte_ext_name}. A VM-enabled legacy (non-CHERI) OS running in {cheri_int_mode_name} will not load or store capabilities, and so the default state of CW=0 causing loaded capabilities to have their tags cleared, and stored capabilities with their tags set to cause a page fault, won't occur. A CHERI-aware OS running a VM-enabled OS is required to support {cheri_pte_ext_name}, and the minimum level of support is to set CW to 1 in all PTEs and leave <<sstatusreg_pte,sstatus>>.CRG and CRG in all PTEs set to 0, which will allow capabilities with their tags set to be loaded and stored successfully.
+A CHERI-aware OS running a VM-enabled OS on an RV64 core is required to support {cheri_pte_ext_name}, and the minimum level of support is to set CW to 1 in all PTEs intended for storing capabilities (i.e. anonymous mappings) and leave <<sstatusreg_pte,sstatus>>.CRG and CRG in all PTEs set to 0, which will allow capabilities with their tags set to be loaded and stored successfully.
+
+Therefore Implementing any RV64 virtual memory translation scheme (_Sv39_, _Sv48_ or _Sv57_) and {cheri_base_ext_name} requires {cheri_pte_ext_name} to be implemented.
You would need to do so extremely early in boot. It'd be a big ugly wart
in the code to do so. Just because you technically can doesn't mean you
should.
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arichardson
approved these changes
Nov 14, 2024
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any objections to merging this? |
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