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arm64: fpsimd: Move SME save/restore inline

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Currently the SVE register save/restore sequences are written in
out-of-line assembly routines. While this works, it's somewhat painful:

* For KVM to use the sequences, portions of the logic will need to be
  duplicated in KVM hyp code. While the common logic can be shared in
  assembly macros, this is very likely to lead to unnecessary divergence
  and be a maintenance burden.

* For historical reasons, the assembly macros take some register
  arguments as numerical indices (e.g. "sme_save_za 0, x2, 12" uses x0, x1, and
  x12), which is simply confusing.

* Address generation and control flow are far clearer in C than in
  assembly.

* The assembly sequences can't be instrumented, and so it's harder than
  necessary to catch memory safety issues.

To handle the above, move the SME register save/restore sequences
to inline assembly.

Neither GCC nor LLVM instrument memory arguments to inline assembly, so
explicit instrumentation is added in the same manner as other assembly
routines. This instrumentation is implicitly disabled by Kbuild for nVHE
hyp code.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Vladimir Murzin <vladimir.murzin@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Fuad Tabba <tabba@google.com>
Cc: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oupton@kernel.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Rutland 2026-06-03 12:06:29 +01:00 • committed by Will Deacon
commit bfdfafd907
4 changed files with 104 additions and 128 deletions
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