Re: [PATCH 05/10] KVM: arm64: Rework SVE host-save/guest-restore

On Wed, 17 Mar 2021 14:29:39 +0000,
Will Deacon [off-list ref] wrote:

On Tue, Mar 16, 2021 at 10:13:07AM +0000, Marc Zyngier wrote:

quoted

In order to keep the code readable, move the host-save/guest-restore
sequences in their own functions, with the following changes:
- the hypervisor ZCR is now set from C code
- ZCR_EL2 is always used as the EL2 accessor

This results in some minor assembler macro rework.
No functional change intended.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/include/asm/fpsimdmacros.h   |  8 +++--
 arch/arm64/include/asm/kvm_hyp.h        |  2 +-
 arch/arm64/kvm/hyp/fpsimd.S             |  2 +-
 arch/arm64/kvm/hyp/include/hyp/switch.h | 41 +++++++++++++++----------
 4 files changed, 33 insertions(+), 20 deletions(-)

[...]

quoted

diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
index fb68271c1a0f..d34dc220a1ce 100644
--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h

@@ -196,6 +196,25 @@ static inline bool __populate_fault_info(struct kvm_vcpu *vcpu)
 	return true;
 }
 
+static inline void __hyp_sve_save_host(struct kvm_vcpu *vcpu)
+{
+	struct thread_struct *thread;
+
+	thread = container_of(vcpu->arch.host_fpsimd_state, struct thread_struct,
+			      uw.fpsimd_state);
+
+	__sve_save_state(sve_pffr(thread), &vcpu->arch.host_fpsimd_state->fpsr);
+}
+
+static inline void __hyp_sve_restore_guest(struct kvm_vcpu *vcpu)
+{
+	if (read_sysreg_s(SYS_ZCR_EL2) != (vcpu_sve_vq(vcpu) - 1))

Strictly speaking, we should probably be extracting the LEN field from
ZCR_EL2, otherwise this has the potential to go horribly wrong if any of
the RES0 bits are allocated in future.

Good point, the equivalent asm macro has a BIC to that effect. I'll
fix that in the next round, as there are similar patterns in a number
of places.

Other than that:

Acked-by: Will Deacon <will@kernel.org>

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.

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