KVM: arm64: Convert lazy FPSIMD context switch trap to C

To make the lazy FPSIMD context switch trap code easier to hack on,
this patch converts it to C.

This is not amazingly efficient, but the trap should typically only
be taken once per host context switch.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm64/kvm/hyp/entry.S

@@ -172,40 +172,27 @@ ENTRY(__fpsimd_guest_restore)
 	// x1: vcpu
 	// x2-x29,lr: vcpu regs
 	// vcpu x0-x1 on the stack
-	stp	x2, x3, [sp, #-16]!
-	stp	x4, lr, [sp, #-16]!
-
-alternative_if_not ARM64_HAS_VIRT_HOST_EXTN
-	mrs	x2, cptr_el2
-	bic	x2, x2, #CPTR_EL2_TFP
-	msr	cptr_el2, x2
-alternative_else
-	mrs	x2, cpacr_el1
-	orr	x2, x2, #CPACR_EL1_FPEN
-	msr	cpacr_el1, x2
-alternative_endif
-	isb
-
-	mov	x3, x1
-
-	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
-
-	// Skip restoring fpexc32 for AArch64 guests
-	mrs	x1, hcr_el2
-	tbnz	x1, #HCR_RW_SHIFT, 1f
-	ldr	x4, [x3, #VCPU_FPEXC32_EL2]
-	msr	fpexc32_el2, x4
-1:
-	ldp	x4, lr, [sp], #16
-	ldp	x2, x3, [sp], #16
-	ldp	x0, x1, [sp], #16
-
+	stp	x2, x3, [sp, #-144]!
+	stp	x4, x5, [sp, #16]
+	stp	x6, x7, [sp, #32]
+	stp	x8, x9, [sp, #48]
+	stp	x10, x11, [sp, #64]
+	stp	x12, x13, [sp, #80]
+	stp	x14, x15, [sp, #96]
+	stp	x16, x17, [sp, #112]
+	stp	x18, lr, [sp, #128]
+
+	bl	__hyp_switch_fpsimd
+
+	ldp	x4, x5, [sp, #16]
+	ldp	x6, x7, [sp, #32]
+	ldp	x8, x9, [sp, #48]
+	ldp	x10, x11, [sp, #64]
+	ldp	x12, x13, [sp, #80]
+	ldp	x14, x15, [sp, #96]
+	ldp	x16, x17, [sp, #112]
+	ldp	x18, lr, [sp, #128]
+	ldp	x0, x1, [sp, #144]
+	ldp	x2, x3, [sp], #160
 	eret
 ENDPROC(__fpsimd_guest_restore)

arch/arm64/kvm/hyp/switch.c

@@ -318,6 +318,30 @@ static bool __hyp_text __skip_instr(struct kvm_vcpu *vcpu)
 	}
 }
 
+void __hyp_text __hyp_switch_fpsimd(u64 esr __always_unused,
+				    struct kvm_vcpu *vcpu)
+{
+	kvm_cpu_context_t *host_ctxt;
+
+	if (has_vhe())
+		write_sysreg(read_sysreg(cpacr_el1) | CPACR_EL1_FPEN,
+			     cpacr_el1);
+	else
+		write_sysreg(read_sysreg(cptr_el2) & ~(u64)CPTR_EL2_TFP,
+			     cptr_el2);
+
+	isb();
+
+	host_ctxt = kern_hyp_va(vcpu->arch.host_cpu_context);
+	__fpsimd_save_state(&host_ctxt->gp_regs.fp_regs);
+	__fpsimd_restore_state(&vcpu->arch.ctxt.gp_regs.fp_regs);
+
+	/* Skip restoring fpexc32 for AArch64 guests */
+	if (!(read_sysreg(hcr_el2) & HCR_RW))
+		write_sysreg(vcpu->arch.ctxt.sys_regs[FPEXC32_EL2],
+			     fpexc32_el2);
+}
+
 /*
  * Return true when we were able to fixup the guest exit and should return to
  * the guest, false when we should restore the host state and return to the