[PATCH v3 0/6] KVM: arm64: Rework FPSIMD/SVE tracking

Marc Zyngier
2021-12-01T12:04:49Z

This is v3 of this series aiming at simplifying the FP handling.

It recently became apparent that we are mapping each vcpu thread's
thread_info structure at EL2 for the sole purpose of checking on the
TIF_FOREIGN_FPSTATE flag.

Given that this looks like a slightly over-engineered way of sharing a
single bit of information, let's move to a slightly more obvious
implementation by maintaining a vcpu-private shadow flag that
represents the same state.

In the same vein, it appears that the code that deals with saving the
host SVE state when used by the guest can never run, and that's by
construction. This is actually a good thing, because it be guaranteed
to explode on nVHE. Let's get rid of it.

I also take this opportunity to add what looks like a missing, and
nonetheless crucial piece of information to the FPSIMD code regarding
the way KVM (ab)uses the TIF_FOREIGN_FPSTATE.

Lightly tested on an A53 box with a bunch of paranoia instances
running in both host and guests, and more heavily on a FVP to check
the SVE behaviour (using the sve-test selftest running in both host
and guest at the same time).

I plan to take this series for a spin in -next immediately.

* From v2 [2]:
- Removed obsolete comments
- Removed __sve_save_state which is now unused

* From v1 [1]:
- New patch getting rid of the host SVE save code
- Reworded the documentation update patch

[1] https://lore.kernel.org/r/20211021151124.3098113-1-maz@kernel.org
[2] https://lore.kernel.org/r/20211028111640.3663631-1-maz@kernel.org

Marc Zyngier (6):
KVM: arm64: Reorder vcpu flag definitions
KVM: arm64: Get rid of host SVE tracking/saving
KVM: arm64: Remove unused __sve_save_state
KVM: arm64: Introduce flag shadowing TIF_FOREIGN_FPSTATE
KVM: arm64: Stop mapping current thread_info at EL2
arm64/fpsimd: Document the use of TIF_FOREIGN_FPSTATE by KVM

arch/arm64/include/asm/kvm_host.h | 29 +++++++++---------
arch/arm64/include/asm/kvm_hyp.h | 1 -
arch/arm64/kernel/fpsimd.c | 6 +++-
arch/arm64/kvm/arm.c | 1 +
arch/arm64/kvm/fpsimd.c | 40 +++++++++----------------
arch/arm64/kvm/hyp/fpsimd.S | 6 ----
arch/arm64/kvm/hyp/include/hyp/switch.h | 30 +++----------------
arch/arm64/kvm/hyp/nvhe/switch.c | 1 -
arch/arm64/kvm/hyp/vhe/switch.c | 1 -
9 files changed, 38 insertions(+), 77 deletions(-)

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2.30.2