arm64: KVM: Implement fpsimd save/restore

Implement the fpsimd save restore, keeping the lazy part in
assembler (as returning to C would be overkill).

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>

arch/arm64/kvm/hyp/Makefile

@@ -9,3 +9,4 @@ obj-$(CONFIG_KVM_ARM_HOST) += sysreg-sr.o
 obj-$(CONFIG_KVM_ARM_HOST) += debug-sr.o
 obj-$(CONFIG_KVM_ARM_HOST) += entry.o
 obj-$(CONFIG_KVM_ARM_HOST) += switch.o
+obj-$(CONFIG_KVM_ARM_HOST) += fpsimd.o

arch/arm64/kvm/hyp/entry.S

@@ -27,6 +27,7 @@
 
 #define CPU_GP_REG_OFFSET(x)	(CPU_GP_REGS + x)
 #define CPU_XREG_OFFSET(x)	CPU_GP_REG_OFFSET(CPU_USER_PT_REGS + 8*x)
+#define CPU_SYSREG_OFFSET(x)	(CPU_SYSREGS + 8*x)
 
 	.text
 	.pushsection	.hyp.text, "ax"
@@ -127,4 +128,33 @@ ENTRY(__guest_exit)
 	ret
 ENDPROC(__guest_exit)
 
-	/* Insert fault handling here */
+ENTRY(__fpsimd_guest_restore)
+	stp	x4, lr, [sp, #-16]!
+
+	mrs	x2, cptr_el2
+	bic	x2, x2, #CPTR_EL2_TFP
+	msr	cptr_el2, x2
+	isb
+
+	mrs	x3, tpidr_el2
+
+	ldr	x0, [x3, #VCPU_HOST_CONTEXT]
+	kern_hyp_va x0
+	add	x0, x0, #CPU_GP_REG_OFFSET(CPU_FP_REGS)
+	bl	__fpsimd_save_state
+
+	add	x2, x3, #VCPU_CONTEXT
+	add	x0, x2, #CPU_GP_REG_OFFSET(CPU_FP_REGS)
+	bl	__fpsimd_restore_state
+
+	mrs	x1, hcr_el2
+	tbnz	x1, #HCR_RW_SHIFT, 1f
+	ldr	x4, [x2, #CPU_SYSREG_OFFSET(FPEXC32_EL2)]
+	msr	fpexc32_el2, x4
+1:
+	ldp	x4, lr, [sp], #16
+	ldp	x2, x3, [sp], #16
+	ldp	x0, x1, [sp], #16
+
+	eret
+ENDPROC(__fpsimd_guest_restore)

arch/arm64/kvm/hyp/fpsimd.S

@@ -0,0 +1,33 @@
+/*
+ * Copyright (C) 2015 - ARM Ltd
+ * Author: Marc Zyngier <marc.zyngier@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/linkage.h>
+
+#include <asm/fpsimdmacros.h>
+
+	.text
+	.pushsection	.hyp.text, "ax"
+
+ENTRY(__fpsimd_save_state)
+	fpsimd_save	x0, 1
+	ret
+ENDPROC(__fpsimd_save_state)
+
+ENTRY(__fpsimd_restore_state)
+	fpsimd_restore	x0, 1
+	ret
+ENDPROC(__fpsimd_restore_state)

arch/arm64/kvm/hyp/hyp.h

@@ -76,6 +76,13 @@ void __debug_restore_state(struct kvm_vcpu *vcpu,
 void __debug_cond_save_host_state(struct kvm_vcpu *vcpu);
 void __debug_cond_restore_host_state(struct kvm_vcpu *vcpu);
 
+void __fpsimd_save_state(struct user_fpsimd_state *fp_regs);
+void __fpsimd_restore_state(struct user_fpsimd_state *fp_regs);
+static inline bool __fpsimd_enabled(void)
+{
+	return !(read_sysreg(cptr_el2) & CPTR_EL2_TFP);
+}
+
 u64 __guest_enter(struct kvm_vcpu *vcpu, struct kvm_cpu_context *host_ctxt);
 
 #endif /* __ARM64_KVM_HYP_H__ */

arch/arm64/kvm/hyp/switch.c

@@ -89,6 +89,7 @@ int __hyp_text __guest_run(struct kvm_vcpu *vcpu)
 {
 	struct kvm_cpu_context *host_ctxt;
 	struct kvm_cpu_context *guest_ctxt;
+	bool fp_enabled;
 	u64 exit_code;
 
 	vcpu = kern_hyp_va(vcpu);
@@ -118,6 +119,8 @@ int __hyp_text __guest_run(struct kvm_vcpu *vcpu)
 	exit_code = __guest_enter(vcpu, host_ctxt);
 	/* And we're baaack! */
 
+	fp_enabled = __fpsimd_enabled();
+
 	__sysreg_save_state(guest_ctxt);
 	__sysreg32_save_state(vcpu);
 	__timer_save_state(vcpu);
@@ -128,6 +131,11 @@ int __hyp_text __guest_run(struct kvm_vcpu *vcpu)
 
 	__sysreg_restore_state(host_ctxt);
 
+	if (fp_enabled) {
+		__fpsimd_save_state(&guest_ctxt->gp_regs.fp_regs);
+		__fpsimd_restore_state(&host_ctxt->gp_regs.fp_regs);
+	}
+
 	__debug_save_state(vcpu, kern_hyp_va(vcpu->arch.debug_ptr), guest_ctxt);
 	__debug_cond_restore_host_state(vcpu);
 

arch/arm64/kvm/hyp/sysreg-sr.c

@@ -107,7 +107,7 @@ 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 (!(read_sysreg(cptr_el2) & CPTR_EL2_TFP))
+	if (__fpsimd_enabled())
 		sysreg[FPEXC32_EL2] = read_sysreg(fpexc32_el2);
 
 	if (vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY)