riscv: Add support for enabling SV48 mode
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Authored by markj on Feb 14 2022, 10:31 PM.

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jhb

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rG31218f3209ac: riscv: Add support for enabling SV48 mode

Summary

This increases the size of the user map from 256GB to 128TB. The kernel
map is left unchanged for now.

For now SV48 mode is left disabled by default, but can be enabled with a
tunable. Note that extant hardware does not implement SV48, but QEMU
does.

In pmap_bootstrap(), allocate a L0 page and attempt to enable SV48 mode. If the write to SATP doesn't take, the kernel continues to run in SV39 mode.
Define VM_MAX_USER_ADDRESS to refer to the SV48 limit. In SV39 mode, the region [VM_MAX_USER_ADDRESS_SV39, VM_MAX_USER_ADDRESS_SV48] is not mappable.

Repository

rS FreeBSD src repository - subversion

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Build Status

Buildable 44449
Build 41337: arc lint + arc unit

markj requested review of this revision.Feb 14 2022, 10:31 PM

jhb added a subscriber: jhb.

jhb added inline comments.

sys/riscv/include/riscvreg.h
153	These changes seem like an unrelated cleanup that could be earlier? Also, does this constant need UL? Perhaps it is auto-promoted as it is already bigger than MAX_INT?
sys/riscv/include/vmparam.h
212	Hmm, I guess I can see from this why you added _SV39 when you did. I would maybe still say to add PS_STRINGS_SV39 in the earlier commit?

This revision is now accepted and ready to land.Feb 15 2022, 12:23 AM

sys/riscv/include/riscvreg.h
153	Yeah, this is here just because this commit adds the first use of SATP_MODE_M. I don't think there's another suitable commit to squash this into. I suppose I could have a separate commit for this part. I'll add the UL suffix here too just for consistency, but yeah I believe it's correct as is.