How to do virtual address translation when satp is not active

[trdthg]

12.4.1. Addressing and Memory Protection said:

A virtual address va is translated into a physical address pa as follows:

1. Let a be satp.ppn×PAGESIZE, and let i=LEVELS-1. (For Sv32, PAGESIZE=212 and LEVELS=2.) The satp register >must be active, i.e., the effective privilege mode must be S-mode or U-mode.

So when satp is not active, how should the translatAddr be implemented?

Convert to paddr with zero_extend directly (Like SBare)?

[gfavor]

If satp is architecturally not "active", then one can't be executing in S/HS and/or U modes (and hence any question about how translation is implemented in these modes is meaningless).

If satp is active and satp.MODE=Bare, then SPA[63:0]=VA[63:0]. Any limitations on the SPA (system physical address) are only imposed downstream by PMAs and/or PMPs. For example, PMAs may effectively say that all >48-bit physical addresses are invalid (and will result in an Access Fault).

[trdthg]

So, for example, in S mode, it is expected that there are only two types of behavior?

• don't perform any operations that require translateAddr
• or satp must be in an active state if needed

[gfavor]

If you're in S-mode, then satp is "active". The only question is what is the satp.MODE field's value, e.g. Bare mode or some translated mode. Whatever that mode is, determines how VAs are "translated/converted" to SPAs.