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Ubuntu 25.10 Raises RISC-V Profile Requirements

(www.omgubuntu.co.uk)
126 points bundie | 1 comments | 01 Jul 25 08:32 UTC | HN request time: 0.301s | source
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csense ◴[03 Jul 25 22:42 UTC] No.44459751[source]▶
Can you write a kernel patch / driver to trap the unsupported instructions and provide software implementations?
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Findecanor ◴[04 Jul 25 07:09 UTC] No.44461893[source]▶
The profile includes not just additional instructions but also architectural requirements that can't be emulated. The size of cache lines and reservation sets must be 64 bytes (there is no instruction to query it, like there is on ARM). Data-independent execution latency is important for protecting cryptography against timing attacks.

Those were already in RVA22, and the difference from that to RVA23 could probably be emulated with traps though.

However, I think that some of the new instructions in RVA23 may potentially become very common in some binaries later on and could possibly trap so often that they would slow down those programs considerably.

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1. bobmcnamara ◴[04 Jul 25 14:07 UTC] No.44464709[source]▶
> The size of cache lines and reservation sets must be 64 bytes (there is no instruction to query it, like there is on ARM)

Thank goodness. What a colossal PITA trying to account for that across cluster switches.