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change Zmct checking to PCC bounds in legacy mode, and change JVTC reset value #178

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merged 3 commits into from
Apr 5, 2024

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fixes #110

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@arichardson arichardson left a comment

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I still think this is data and should probably use DDC rather than PCC in legacy mode (even though the base extension requires X permission). I also don't believe we should be requiring X permission in the capability. The base extension has X required in the page tables/pmp which should be enough to keep "weird" uarches working.

I'd also like to see a review from @jrtc27 before merging.

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Zcmt defines that the fetch from the table is from instruction memory. The overall instruction executed is effectively 48-bit, with 16-bits from CM.JALT/CM.JT, the other 32-bits (for RV32) from the table.

Therefore PCC is used to authorise in legacy mode, as the fetch is designated to be from instruction memory in the risc-v specification.

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LGTM with the note explaining why PCC is used instead of DDC.

@tariqkurd-repo tariqkurd-repo merged commit 35fadd2 into riscv:main Apr 5, 2024
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Behaviour of JVTC in legacy mode
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