Re: [PATCH v3 0/8] KVM: arm64: FPSIMD/SVE/SME fixes

On Mon, Feb 10, 2025 at 07:52:18PM +0000, Mark Rutland wrote:

These patches fix some issues with the way KVM manages FPSIMD/SVE/SME
state. The series supersedes my earlier attempt at fixing the host SVE
state corruption issue:

  https://lore.kernel.org/linux-arm-kernel/20250121100026.3974971-1-mark.rutland@arm.com/ (local)

Patch 1 addresses the host SVE state corruption issue by always saving
and unbinding the host state when loading a vCPU, as discussed on the
earlier patch:

  https://lore.kernel.org/linux-arm-kernel/Z4--YuG5SWrP_pW7@J2N7QTR9R3/ (local)
  https://lore.kernel.org/linux-arm-kernel/86plkful48.wl-maz@kernel.org/ (local)

Patches 2 to 4 remove code made redundant by patch 1. These probably
warrant backporting along with patch 1 as there is some historical
brokenness in the code they remove.

Patches 5 to 7 are preparatory refactoring for patch 8, and are not
intended to have any functional impact.

Patch 8 addresses some mismanagement of ZCR_EL{1,2} which can result in
the host VMM unexpectedly receiving a SIGKILL. To fix this, we eagerly
switch ZCR_EL{1,2} at guest<->host transitions, as discussed on another
series:

  https://lore.kernel.org/linux-arm-kernel/Z4pAMaEYvdLpmbg2@J2N7QTR9R3/ (local)
  https://lore.kernel.org/linux-arm-kernel/86o6zzukwr.wl-maz@kernel.org/ (local)
  https://lore.kernel.org/linux-arm-kernel/Z5Dc-WMu2azhTuMn@J2N7QTR9R3/ (local)

The end result is that KVM loses ~100 lines of code, and becomes a bit
simpler to reason about.

LGTM, although a minor nitpick would be to repack the host data flags at
the end of purging SVE/SME.

Reviewed-by: Oliver Upton <redacted>

-- 
Thanks,
Oliver