arm64: KVM: Implement guest entry

Contrary to the previous patch, the guest entry is fairly different
from its assembly counterpart, mostly because it is only concerned
with saving/restoring the GP registers, and nothing else.
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm64/kvm/hyp/Makefile

@@ -7,3 +7,4 @@ obj-$(CONFIG_KVM_ARM_HOST) += vgic-v3-sr.o
 obj-$(CONFIG_KVM_ARM_HOST) += timer-sr.o
 obj-$(CONFIG_KVM_ARM_HOST) += sysreg-sr.o
 obj-$(CONFIG_KVM_ARM_HOST) += debug-sr.o
+obj-$(CONFIG_KVM_ARM_HOST) += entry.o

arch/arm64/kvm/hyp/entry.S

+/*
+ * 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/asm-offsets.h>
+#include <asm/assembler.h>
+#include <asm/fpsimdmacros.h>
+#include <asm/kvm.h>
+#include <asm/kvm_arm.h>
+#include <asm/kvm_asm.h>
+#include <asm/kvm_mmu.h>
+
+#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)
+
+	.text
+	.pushsection	.hyp.text, "ax"
+
+.macro save_callee_saved_regs ctxt
+	stp	x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)]
+	stp	x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)]
+	stp	x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)]
+	stp	x25, x26, [\ctxt, #CPU_XREG_OFFSET(25)]
+	stp	x27, x28, [\ctxt, #CPU_XREG_OFFSET(27)]
+	stp	x29, lr,  [\ctxt, #CPU_XREG_OFFSET(29)]
+.endm
+
+.macro restore_callee_saved_regs ctxt
+	ldp	x19, x20, [\ctxt, #CPU_XREG_OFFSET(19)]
+	ldp	x21, x22, [\ctxt, #CPU_XREG_OFFSET(21)]
+	ldp	x23, x24, [\ctxt, #CPU_XREG_OFFSET(23)]
+	ldp	x25, x26, [\ctxt, #CPU_XREG_OFFSET(25)]
+	ldp	x27, x28, [\ctxt, #CPU_XREG_OFFSET(27)]
+	ldp	x29, lr,  [\ctxt, #CPU_XREG_OFFSET(29)]
+.endm
+
+/*
+ * u64 __guest_enter(struct kvm_vcpu *vcpu,
+ *		     struct kvm_cpu_context *host_ctxt);
+ */
+ENTRY(__guest_enter)
+	// x0: vcpu
+	// x1: host/guest context
+	// x2-x18: clobbered by macros
+
+	// Store the host regs
+	save_callee_saved_regs x1
+
+	// Preserve vcpu & host_ctxt for use at exit time
+	stp	x0, x1, [sp, #-16]!
+
+	add	x1, x0, #VCPU_CONTEXT
+
+	// Prepare x0-x1 for later restore by pushing them onto the stack
+	ldp	x2, x3, [x1, #CPU_XREG_OFFSET(0)]
+	stp	x2, x3, [sp, #-16]!
+
+	// x2-x18
+	ldp	x2, x3,   [x1, #CPU_XREG_OFFSET(2)]
+	ldp	x4, x5,   [x1, #CPU_XREG_OFFSET(4)]
+	ldp	x6, x7,   [x1, #CPU_XREG_OFFSET(6)]
+	ldp	x8, x9,   [x1, #CPU_XREG_OFFSET(8)]
+	ldp	x10, x11, [x1, #CPU_XREG_OFFSET(10)]
+	ldp	x12, x13, [x1, #CPU_XREG_OFFSET(12)]
+	ldp	x14, x15, [x1, #CPU_XREG_OFFSET(14)]
+	ldp	x16, x17, [x1, #CPU_XREG_OFFSET(16)]
+	ldr	x18,      [x1, #CPU_XREG_OFFSET(18)]
+
+	// x19-x29, lr
+	restore_callee_saved_regs x1
+
+	// Last bits of the 64bit state
+	ldp	x0, x1, [sp], #16
+
+	// Do not touch any register after this!
+	eret
+ENDPROC(__guest_enter)
+
+ENTRY(__guest_exit)
+	// x0: vcpu
+	// x1: return code
+	// x2-x3: free
+	// x4-x29,lr: vcpu regs
+	// vcpu x0-x3 on the stack
+
+	add	x2, x0, #VCPU_CONTEXT
+
+	stp	x4, x5,   [x2, #CPU_XREG_OFFSET(4)]
+	stp	x6, x7,   [x2, #CPU_XREG_OFFSET(6)]
+	stp	x8, x9,   [x2, #CPU_XREG_OFFSET(8)]
+	stp	x10, x11, [x2, #CPU_XREG_OFFSET(10)]
+	stp	x12, x13, [x2, #CPU_XREG_OFFSET(12)]
+	stp	x14, x15, [x2, #CPU_XREG_OFFSET(14)]
+	stp	x16, x17, [x2, #CPU_XREG_OFFSET(16)]
+	str	x18,      [x2, #CPU_XREG_OFFSET(18)]
+
+	ldp	x6, x7, [sp], #16	// x2, x3
+	ldp	x4, x5, [sp], #16	// x0, x1
+
+	stp	x4, x5, [x2, #CPU_XREG_OFFSET(0)]
+	stp	x6, x7, [x2, #CPU_XREG_OFFSET(2)]
+
+	save_callee_saved_regs x2
+
+	// Restore vcpu & host_ctxt from the stack
+	// (preserving return code in x1)
+	ldp	x0, x2, [sp], #16
+	// Now restore the host regs
+	restore_callee_saved_regs x2
+
+	mov	x0, x1
+	ret
+ENDPROC(__guest_exit)
+
+	/* Insert fault handling here */

arch/arm64/kvm/hyp/hyp.h

@@ -52,5 +52,7 @@ 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);
 
+u64 __guest_enter(struct kvm_vcpu *vcpu, struct kvm_cpu_context *host_ctxt);
+
 #endif /* __ARM64_KVM_HYP_H__ */