arm64: Initial SVE support
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Authored by andrew on Jan 4 2024, 12:32 PM.

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kib
markj
manu

Group Reviewers

arm64

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rG2c5961fff4e5: arm64: Initial SVE support
rG332c426328db: arm64: Initial SVE support

Summary

Add initial kernel support for SVE. This detects if SVE is present on
all CPUs, and if so allows for the use of SVE in the future.

As the SVE registers are a superset of the VFP registers we don't need
to restore the VFP registers when SVE is enabled.

Ths interface to enable SVE is provided, but not used until SVE is
supported in signals and with ptrace.

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rG FreeBSD src repository

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Buildable 55236
Build 52125: arc lint + arc unit

Event Timeline

andrew created this revision.Jan 4 2024, 12:32 PM

Herald added a reviewer: manu. · View Herald TranscriptJan 4 2024, 12:32 PM

Herald added subscribers: emaste, imp. · View Herald Transcript

andrew requested review of this revision.Jan 4 2024, 12:32 PM

andrew added a parent revision: D43305: arm64: Create a version of vfp_save_state for cpu_switch.

Harbormaster completed remote builds in B55236: Diff 132253.Jan 4 2024, 12:32 PM

andrew added a child revision: D43307: arm64: Add the SVE registers to the signal frame.Jan 4 2024, 12:32 PM

This one seems reasonable, but it would be best to get others to say so too.

sys/arm64/arm64/vfp.c
111	Do you want to leave this in?
622	should you free the svesaved memory instead?

andrew added a parent revision: D44807: arm64: Clear td_frame when returning to userspace.Apr 16 2024, 3:43 PM

Rework to not guarentee the SVE registers are saved over a syscall other than sigreturn.
The ABI doesn't require SVE registers to be saved on a function call so extend this to a system call.
As dropping the SVE state on all system calls could get expensive only do it on context switch when in one.

Harbormaster completed remote builds in B57123: Diff 137103.Apr 16 2024, 3:47 PM

In D43306#1021418, @andrew wrote:

Rework to not guarentee the SVE registers are saved over a syscall other than sigreturn.
The ABI doesn't require SVE registers to be saved on a function call so extend this to a system call.
As dropping the SVE state on all system calls could get expensive only do it on context switch when in one.

I read this as disallowing use of rtld for any custom ABI. Imagine that rtld bind is called to resolve a symbol which use custom calling conventions (namely, preserving SVE state). Then, if rtld ever needed to issue a syscall while working, it corrupts the SVE state of the caller.

Functions that take an SVE register as an argument, or use one for the return value are marked with STO_AARCH64_VARIANT_PCS [1]. In glibc it looks like they avoid lazy resolution for all variant pcs functions. As there are more reasons than just SVE for a function to be marked as a variant, and more reasons could be added in the future I think it's the only safe option.

[1] https://github.com/ARM-software/abi-aa/blob/main/aaelf64/aaelf64.rst#st_other-values

rebase + remove tf_flags to detect when we are in a syscall

Harbormaster completed remote builds in B58161: Diff 139800.Jun 13 2024, 1:23 PM

fuz added a subscriber: fuz.Jul 29 2024, 1:25 PM

This revision was not accepted when it landed; it landed in state Needs Review.Sep 30 2024, 12:23 PM

Closed by commit rG332c426328db: arm64: Initial SVE support (authored by andrew). · Explain Why

This revision was automatically updated to reflect the committed changes.

andrew added a commit: rG332c426328db: arm64: Initial SVE support.

andrew added a commit: rG2c5961fff4e5: arm64: Initial SVE support.Oct 21 2024, 3:05 PM