[PATCH 2/2] KVM/arm: enable armv7 fp/simd lazy switch

[Mario Smarduch]

Adds code to enable fp/simd lazy switch. On each entry check if fp/simd
registers have been switched to guest, if no set the trap flag. On trap 
switch fp/simd registers and set vfp_lazy to true and disable trapping. 
When the vcpu is about to be put, then context switch fp/simd registers
save guest and restore host and reset the vfp_lazy state to enable trapping 
again.

Signed-off-by: Mario Smarduch <m.smarduch at samsung.com>
---
 arch/arm/kvm/arm.c        | 17 +++++++++++++++++
 arch/arm/kvm/interrupts.S | 40 +++++++++++++++++++++++++++++-----------
 2 files changed, 46 insertions(+), 11 deletions(-)

diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
index ce404a5..0acbb69 100644
--- a/arch/arm/kvm/arm.c
+++ b/arch/arm/kvm/arm.c
@@ -105,6 +105,20 @@ void kvm_arch_check_processor_compat(void *rtn)
 	*(int *)rtn = 0;
 }
 
+/**
+ * kvm_switch_fp_regs() - switch guest/host VFP/SIMD registers
+ * @vcpu:      pointer to vcpu structure.
+ *
+ */
+static void kvm_switch_fp_regs(struct kvm_vcpu *vcpu)
+{
+#ifdef CONFIG_ARM
+	if (vcpu->arch.vfp_lazy == 1) {
+		kvm_call_hyp(__kvm_restore_host_vfp_state, vcpu);
+		vcpu->arch.vfp_lazy = 0;
+	}
+#endif
+}
 
 /**
  * kvm_arch_init_vm - initializes a VM data structure
@@ -295,6 +309,9 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 {
+	/* Check if Guest accessed VFP registers */
+	kvm_switch_fp_regs(vcpu);
+
 	/*
 	 * The arch-generic KVM code expects the cpu field of a vcpu to be -1
 	 * if the vcpu is no longer assigned to a cpu.  This is used for the
diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S
index 900ef6d..a47acc1 100644
--- a/arch/arm/kvm/interrupts.S
+++ b/arch/arm/kvm/interrupts.S
@@ -96,6 +96,24 @@ ENTRY(__kvm_flush_vm_context)
 	bx	lr
 ENDPROC(__kvm_flush_vm_context)
 
+/**
+ * void __kvm_restore_host_vfp_state(struct vcpu *vcpu) - Executes a lazy
+ *	fp/simd switch, saves the guest, restores host.
+ *
+ */
+ENTRY(__kvm_restore_host_vfp_state)
+	push    {r3-r7}
+
+	add     r7, r0, #VCPU_VFP_GUEST
+	store_vfp_state r7
+
+	add     r7, r0, #VCPU_VFP_HOST
+	ldr     r7, [r7]
+	restore_vfp_state r7
+
+	pop     {r3-r7}
+	bx      lr
+ENDPROC(__kvm_restore_host_vfp_state)
 
 /********************************************************************
  *  Hypervisor world-switch code
@@ -131,7 +149,14 @@ ENTRY(__kvm_vcpu_run)
 
 	@ Trap coprocessor CRx accesses
 	set_hstr vmentry
+
+	ldr     r1, [vcpu, #VCPU_VFP_LAZY]
+	cmp     r1, #1
+	beq     skip_guest_vfp_trap
+
 	set_hcptr vmentry, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11))
+skip_guest_vfp_trap:
+
 	set_hdcr vmentry
 
 	@ Write configured ID register into MIDR alias
@@ -170,22 +195,12 @@ __kvm_vcpu_return:
 	@ Don't trap coprocessor accesses for host kernel
 	set_hstr vmexit
 	set_hdcr vmexit
-	set_hcptr vmexit, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11)), after_vfp_restore
+	set_hcptr vmexit, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11))
 
 #ifdef CONFIG_VFPv3
-	@ Switch VFP/NEON hardware state to the host's
-	add	r7, vcpu, #VCPU_VFP_GUEST
-	store_vfp_state r7
-	add	r7, vcpu, #VCPU_VFP_HOST
-	ldr	r7, [r7]
-	restore_vfp_state r7
-
-after_vfp_restore:
 	@ Restore FPEXC_EN which we clobbered on entry
 	pop	{r2}
 	VFPFMXR FPEXC, r2
-#else
-after_vfp_restore:
 #endif
 
 	@ Reset Hyp-role
@@ -485,6 +500,9 @@ switch_to_guest_vfp:
 	@ NEON/VFP used.  Turn on VFP access.
 	set_hcptr vmtrap, (HCPTR_TCP(10) | HCPTR_TCP(11))
 
+	mov     r1, #1
+	str     r1, [vcpu, #VCPU_VFP_LAZY]
+
 	@ Switch VFP/NEON hardware state to the guest's
 	add	r7, r0, #VCPU_VFP_HOST
 	ldr	r7, [r7]
-- 
1.9.1