[PATCH v3 31/41] KVM: arm64: Defer saving/restoring 32-bit sysregs to vcpu load/put

[Christoffer Dall]

When running a 32-bit VM (EL1 in AArch32), the AArch32 system registers
can be deferred to vcpu load/put on VHE systems because neither
the host kernel nor host userspace uses these registers.

Note that we can no longer save/restore DBGVCR32_EL2 conditionally based
on the state of the debug dirty flag on VHE, but since we do the
load/put pretty rarely, this comes out as a win anyway.

Signed-off-by: Christoffer Dall <christoffer.dall at linaro.org>
---
 arch/arm64/kvm/hyp/switch.c    |  6 ------
 arch/arm64/kvm/hyp/sysreg-sr.c | 12 ++++++++++--
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/kvm/hyp/switch.c b/arch/arm64/kvm/hyp/switch.c
index 2e04d404ac82..05f266b505ce 100644
--- a/arch/arm64/kvm/hyp/switch.c
+++ b/arch/arm64/kvm/hyp/switch.c
@@ -355,11 +355,6 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
 
 	__vgic_restore_state(vcpu);
 
-	/*
-	 * We must restore the 32-bit state before the sysregs, thanks
-	 * to erratum #852523 (Cortex-A57) or #853709 (Cortex-A72).
-	 */
-	__sysreg32_restore_state(vcpu);
 	sysreg_restore_guest_state_vhe(guest_ctxt);
 	__debug_switch_to_guest(vcpu);
 
@@ -371,7 +366,6 @@ int kvm_vcpu_run_vhe(struct kvm_vcpu *vcpu)
 	} while (fixup_guest_exit(vcpu, &exit_code));
 
 	sysreg_save_guest_state_vhe(guest_ctxt);
-	__sysreg32_save_state(vcpu);
 	__vgic_save_state(vcpu);
 
 	__deactivate_traps(vcpu);
diff --git a/arch/arm64/kvm/hyp/sysreg-sr.c b/arch/arm64/kvm/hyp/sysreg-sr.c
index eabd35154232..d225f5797651 100644
--- a/arch/arm64/kvm/hyp/sysreg-sr.c
+++ b/arch/arm64/kvm/hyp/sysreg-sr.c
@@ -195,7 +195,7 @@ void __hyp_text __sysreg32_save_state(struct kvm_vcpu *vcpu)
 	sysreg[DACR32_EL2] = read_sysreg(dacr32_el2);
 	sysreg[IFSR32_EL2] = read_sysreg(ifsr32_el2);
 
-	if (vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY)
+	if (has_vhe() || vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY)
 		sysreg[DBGVCR32_EL2] = read_sysreg(dbgvcr32_el2);
 }
 
@@ -217,7 +217,7 @@ void __hyp_text __sysreg32_restore_state(struct kvm_vcpu *vcpu)
 	write_sysreg(sysreg[DACR32_EL2], dacr32_el2);
 	write_sysreg(sysreg[IFSR32_EL2], ifsr32_el2);
 
-	if (vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY)
+	if (has_vhe() || vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY)
 		write_sysreg(sysreg[DBGVCR32_EL2], dbgvcr32_el2);
 }
 
@@ -242,6 +242,13 @@ void kvm_vcpu_load_sysregs(struct kvm_vcpu *vcpu)
 
 	__sysreg_save_user_state(host_ctxt);
 
+	/*
+	 * Load guest EL1 and user state
+	 *
+	 * We must restore the 32-bit state before the sysregs, thanks
+	 * to erratum #852523 (Cortex-A57) or #853709 (Cortex-A72).
+	 */
+	__sysreg32_restore_state(vcpu);
 	__sysreg_restore_user_state(guest_ctxt);
 	__sysreg_restore_el1_state(guest_ctxt);
 
@@ -280,6 +287,7 @@ void kvm_vcpu_put_sysregs(struct kvm_vcpu *vcpu)
 
 	__sysreg_save_el1_state(guest_ctxt);
 	__sysreg_save_user_state(guest_ctxt);
+	__sysreg32_save_state(vcpu);
 
 	/* Restore host user state */
 	__sysreg_restore_user_state(host_ctxt);
-- 
2.14.2