Linux-libre 4.8.2-gnupck-4.8.2-gnu

1 files changed, 701 insertions, 0 deletions

diff --git a/arch/mips/kvm/entry.c b/arch/mips/kvm/entry.c
new file mode 100644
index 000000000..6a02b3a3f
--- /dev/null
+++ b/arch/mips/kvm/entry.c
@@ -0,0 +1,701 @@
+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Generation of main entry point for the guest, exception handling.
+ *
+ * Copyright (C) 2012  MIPS Technologies, Inc.
+ * Authors: Sanjay Lal <sanjayl@kymasys.com>
+ *
+ * Copyright (C) 2016 Imagination Technologies Ltd.
+ */
+
+#include <linux/kvm_host.h>
+#include <asm/msa.h>
+#include <asm/setup.h>
+#include <asm/uasm.h>
+
+/* Register names */
+#define ZERO		0
+#define AT		1
+#define V0		2
+#define V1		3
+#define A0		4
+#define A1		5
+
+#if _MIPS_SIM == _MIPS_SIM_ABI32
+#define T0		8
+#define T1		9
+#define T2		10
+#define T3		11
+#endif /* _MIPS_SIM == _MIPS_SIM_ABI32 */
+
+#if _MIPS_SIM == _MIPS_SIM_ABI64 || _MIPS_SIM == _MIPS_SIM_NABI32
+#define T0		12
+#define T1		13
+#define T2		14
+#define T3		15
+#endif /* _MIPS_SIM == _MIPS_SIM_ABI64 || _MIPS_SIM == _MIPS_SIM_NABI32 */
+
+#define S0		16
+#define S1		17
+#define T9		25
+#define K0		26
+#define K1		27
+#define GP		28
+#define SP		29
+#define RA		31
+
+/* Some CP0 registers */
+#define C0_HWRENA	7, 0
+#define C0_BADVADDR	8, 0
+#define C0_ENTRYHI	10, 0
+#define C0_STATUS	12, 0
+#define C0_CAUSE	13, 0
+#define C0_EPC		14, 0
+#define C0_EBASE	15, 1
+#define C0_CONFIG5	16, 5
+#define C0_DDATA_LO	28, 3
+#define C0_ERROREPC	30, 0
+
+#define CALLFRAME_SIZ   32
+
+#ifdef CONFIG_64BIT
+#define ST0_KX_IF_64	ST0_KX
+#else
+#define ST0_KX_IF_64	0
+#endif
+
+static unsigned int scratch_vcpu[2] = { C0_DDATA_LO };
+static unsigned int scratch_tmp[2] = { C0_ERROREPC };
+
+enum label_id {
+	label_fpu_1 = 1,
+	label_msa_1,
+	label_return_to_host,
+	label_kernel_asid,
+	label_exit_common,
+};
+
+UASM_L_LA(_fpu_1)
+UASM_L_LA(_msa_1)
+UASM_L_LA(_return_to_host)
+UASM_L_LA(_kernel_asid)
+UASM_L_LA(_exit_common)
+
+static void *kvm_mips_build_enter_guest(void *addr);
+static void *kvm_mips_build_ret_from_exit(void *addr);
+static void *kvm_mips_build_ret_to_guest(void *addr);
+static void *kvm_mips_build_ret_to_host(void *addr);
+
+/**
+ * kvm_mips_entry_setup() - Perform global setup for entry code.
+ *
+ * Perform global setup for entry code, such as choosing a scratch register.
+ *
+ * Returns:	0 on success.
+ *		-errno on failure.
+ */
+int kvm_mips_entry_setup(void)
+{
+	/*
+	 * We prefer to use KScratchN registers if they are available over the
+	 * defaults above, which may not work on all cores.
+	 */
+	unsigned int kscratch_mask = cpu_data[0].kscratch_mask & 0xfc;
+
+	/* Pick a scratch register for storing VCPU */
+	if (kscratch_mask) {
+		scratch_vcpu[0] = 31;
+		scratch_vcpu[1] = ffs(kscratch_mask) - 1;
+		kscratch_mask &= ~BIT(scratch_vcpu[1]);
+	}
+
+	/* Pick a scratch register to use as a temp for saving state */
+	if (kscratch_mask) {
+		scratch_tmp[0] = 31;
+		scratch_tmp[1] = ffs(kscratch_mask) - 1;
+		kscratch_mask &= ~BIT(scratch_tmp[1]);
+	}
+
+	return 0;
+}
+
+static void kvm_mips_build_save_scratch(u32 **p, unsigned int tmp,
+					unsigned int frame)
+{
+	/* Save the VCPU scratch register value in cp0_epc of the stack frame */
+	UASM_i_MFC0(p, tmp, scratch_vcpu[0], scratch_vcpu[1]);
+	UASM_i_SW(p, tmp, offsetof(struct pt_regs, cp0_epc), frame);
+
+	/* Save the temp scratch register value in cp0_cause of stack frame */
+	if (scratch_tmp[0] == 31) {
+		UASM_i_MFC0(p, tmp, scratch_tmp[0], scratch_tmp[1]);
+		UASM_i_SW(p, tmp, offsetof(struct pt_regs, cp0_cause), frame);
+	}
+}
+
+static void kvm_mips_build_restore_scratch(u32 **p, unsigned int tmp,
+					   unsigned int frame)
+{
+	/*
+	 * Restore host scratch register values saved by
+	 * kvm_mips_build_save_scratch().
+	 */
+	UASM_i_LW(p, tmp, offsetof(struct pt_regs, cp0_epc), frame);
+	UASM_i_MTC0(p, tmp, scratch_vcpu[0], scratch_vcpu[1]);
+
+	if (scratch_tmp[0] == 31) {
+		UASM_i_LW(p, tmp, offsetof(struct pt_regs, cp0_cause), frame);
+		UASM_i_MTC0(p, tmp, scratch_tmp[0], scratch_tmp[1]);
+	}
+}
+
+/**
+ * build_set_exc_base() - Assemble code to write exception base address.
+ * @p:		Code buffer pointer.
+ * @reg:	Source register (generated code may set WG bit in @reg).
+ *
+ * Assemble code to modify the exception base address in the EBase register,
+ * using the appropriately sized access and setting the WG bit if necessary.
+ */
+static inline void build_set_exc_base(u32 **p, unsigned int reg)
+{
+	if (cpu_has_ebase_wg) {
+		/* Set WG so that all the bits get written */
+		uasm_i_ori(p, reg, reg, MIPS_EBASE_WG);
+		UASM_i_MTC0(p, reg, C0_EBASE);
+	} else {
+		uasm_i_mtc0(p, reg, C0_EBASE);
+	}
+}
+
+/**
+ * kvm_mips_build_vcpu_run() - Assemble function to start running a guest VCPU.
+ * @addr:	Address to start writing code.
+ *
+ * Assemble the start of the vcpu_run function to run a guest VCPU. The function
+ * conforms to the following prototype:
+ *
+ * int vcpu_run(struct kvm_run *run, struct kvm_vcpu *vcpu);
+ *
+ * The exit from the guest and return to the caller is handled by the code
+ * generated by kvm_mips_build_ret_to_host().
+ *
+ * Returns:	Next address after end of written function.
+ */
+void *kvm_mips_build_vcpu_run(void *addr)
+{
+	u32 *p = addr;
+	unsigned int i;
+
+	/*
+	 * A0: run
+	 * A1: vcpu
+	 */
+
+	/* k0/k1 not being used in host kernel context */
+	UASM_i_ADDIU(&p, K1, SP, -(int)sizeof(struct pt_regs));
+	for (i = 16; i < 32; ++i) {
+		if (i == 24)
+			i = 28;
+		UASM_i_SW(&p, i, offsetof(struct pt_regs, regs[i]), K1);
+	}
+
+	/* Save host status */
+	uasm_i_mfc0(&p, V0, C0_STATUS);
+	UASM_i_SW(&p, V0, offsetof(struct pt_regs, cp0_status), K1);
+
+	/* Save scratch registers, will be used to store pointer to vcpu etc */
+	kvm_mips_build_save_scratch(&p, V1, K1);
+
+	/* VCPU scratch register has pointer to vcpu */
+	UASM_i_MTC0(&p, A1, scratch_vcpu[0], scratch_vcpu[1]);
+
+	/* Offset into vcpu->arch */
+	UASM_i_ADDIU(&p, K1, A1, offsetof(struct kvm_vcpu, arch));
+
+	/*
+	 * Save the host stack to VCPU, used for exception processing
+	 * when we exit from the Guest
+	 */
+	UASM_i_SW(&p, SP, offsetof(struct kvm_vcpu_arch, host_stack), K1);
+
+	/* Save the kernel gp as well */
+	UASM_i_SW(&p, GP, offsetof(struct kvm_vcpu_arch, host_gp), K1);
+
+	/*
+	 * Setup status register for running the guest in UM, interrupts
+	 * are disabled
+	 */
+	UASM_i_LA(&p, K0, ST0_EXL | KSU_USER | ST0_BEV | ST0_KX_IF_64);
+	uasm_i_mtc0(&p, K0, C0_STATUS);
+	uasm_i_ehb(&p);
+
+	/* load up the new EBASE */
+	UASM_i_LW(&p, K0, offsetof(struct kvm_vcpu_arch, guest_ebase), K1);
+	build_set_exc_base(&p, K0);
+
+	/*
+	 * Now that the new EBASE has been loaded, unset BEV, set
+	 * interrupt mask as it was but make sure that timer interrupts
+	 * are enabled
+	 */
+	uasm_i_addiu(&p, K0, ZERO, ST0_EXL | KSU_USER | ST0_IE | ST0_KX_IF_64);
+	uasm_i_andi(&p, V0, V0, ST0_IM);
+	uasm_i_or(&p, K0, K0, V0);
+	uasm_i_mtc0(&p, K0, C0_STATUS);
+	uasm_i_ehb(&p);
+
+	p = kvm_mips_build_enter_guest(p);
+
+	return p;
+}
+
+/**
+ * kvm_mips_build_enter_guest() - Assemble code to resume guest execution.
+ * @addr:	Address to start writing code.
+ *
+ * Assemble the code to resume guest execution. This code is common between the
+ * initial entry into the guest from the host, and returning from the exit
+ * handler back to the guest.
+ *
+ * Returns:	Next address after end of written function.
+ */
+static void *kvm_mips_build_enter_guest(void *addr)
+{
+	u32 *p = addr;
+	unsigned int i;
+	struct uasm_label labels[2];
+	struct uasm_reloc relocs[2];
+	struct uasm_label *l = labels;
+	struct uasm_reloc *r = relocs;
+
+	memset(labels, 0, sizeof(labels));
+	memset(relocs, 0, sizeof(relocs));
+
+	/* Set Guest EPC */
+	UASM_i_LW(&p, T0, offsetof(struct kvm_vcpu_arch, pc), K1);
+	UASM_i_MTC0(&p, T0, C0_EPC);
+
+	/* Set the ASID for the Guest Kernel */
+	UASM_i_LW(&p, T0, offsetof(struct kvm_vcpu_arch, cop0), K1);
+	UASM_i_LW(&p, T0, offsetof(struct mips_coproc, reg[MIPS_CP0_STATUS][0]),
+		  T0);
+	uasm_i_andi(&p, T0, T0, KSU_USER | ST0_ERL | ST0_EXL);
+	uasm_i_xori(&p, T0, T0, KSU_USER);
+	uasm_il_bnez(&p, &r, T0, label_kernel_asid);
+	 UASM_i_ADDIU(&p, T1, K1,
+		      offsetof(struct kvm_vcpu_arch, guest_kernel_asid));
+	/* else user */
+	UASM_i_ADDIU(&p, T1, K1,
+		     offsetof(struct kvm_vcpu_arch, guest_user_asid));
+	uasm_l_kernel_asid(&l, p);
+
+	/* t1: contains the base of the ASID array, need to get the cpu id  */
+	/* smp_processor_id */
+	uasm_i_lw(&p, T2, offsetof(struct thread_info, cpu), GP);
+	/* x4 */
+	uasm_i_sll(&p, T2, T2, 2);
+	UASM_i_ADDU(&p, T3, T1, T2);
+	uasm_i_lw(&p, K0, 0, T3);
+#ifdef CONFIG_MIPS_ASID_BITS_VARIABLE
+	/* x sizeof(struct cpuinfo_mips)/4 */
+	uasm_i_addiu(&p, T3, ZERO, sizeof(struct cpuinfo_mips)/4);
+	uasm_i_mul(&p, T2, T2, T3);
+
+	UASM_i_LA_mostly(&p, AT, (long)&cpu_data[0].asid_mask);
+	UASM_i_ADDU(&p, AT, AT, T2);
+	UASM_i_LW(&p, T2, uasm_rel_lo((long)&cpu_data[0].asid_mask), AT);
+	uasm_i_and(&p, K0, K0, T2);
+#else
+	uasm_i_andi(&p, K0, K0, MIPS_ENTRYHI_ASID);
+#endif
+	uasm_i_mtc0(&p, K0, C0_ENTRYHI);
+	uasm_i_ehb(&p);
+
+	/* Disable RDHWR access */
+	uasm_i_mtc0(&p, ZERO, C0_HWRENA);
+
+	/* load the guest context from VCPU and return */
+	for (i = 1; i < 32; ++i) {
+		/* Guest k0/k1 loaded later */
+		if (i == K0 || i == K1)
+			continue;
+		UASM_i_LW(&p, i, offsetof(struct kvm_vcpu_arch, gprs[i]), K1);
+	}
+
+#ifndef CONFIG_CPU_MIPSR6
+	/* Restore hi/lo */
+	UASM_i_LW(&p, K0, offsetof(struct kvm_vcpu_arch, hi), K1);
+	uasm_i_mthi(&p, K0);
+
+	UASM_i_LW(&p, K0, offsetof(struct kvm_vcpu_arch, lo), K1);
+	uasm_i_mtlo(&p, K0);
+#endif
+
+	/* Restore the guest's k0/k1 registers */
+	UASM_i_LW(&p, K0, offsetof(struct kvm_vcpu_arch, gprs[K0]), K1);
+	UASM_i_LW(&p, K1, offsetof(struct kvm_vcpu_arch, gprs[K1]), K1);
+
+	/* Jump to guest */
+	uasm_i_eret(&p);
+
+	uasm_resolve_relocs(relocs, labels);
+
+	return p;
+}
+
+/**
+ * kvm_mips_build_exception() - Assemble first level guest exception handler.
+ * @addr:	Address to start writing code.
+ * @handler:	Address of common handler (within range of @addr).
+ *
+ * Assemble exception vector code for guest execution. The generated vector will
+ * branch to the common exception handler generated by kvm_mips_build_exit().
+ *
+ * Returns:	Next address after end of written function.
+ */
+void *kvm_mips_build_exception(void *addr, void *handler)
+{
+	u32 *p = addr;
+	struct uasm_label labels[2];
+	struct uasm_reloc relocs[2];
+	struct uasm_label *l = labels;
+	struct uasm_reloc *r = relocs;
+
+	memset(labels, 0, sizeof(labels));
+	memset(relocs, 0, sizeof(relocs));
+
+	/* Save guest k1 into scratch register */
+	UASM_i_MTC0(&p, K1, scratch_tmp[0], scratch_tmp[1]);
+
+	/* Get the VCPU pointer from the VCPU scratch register */
+	UASM_i_MFC0(&p, K1, scratch_vcpu[0], scratch_vcpu[1]);
+	UASM_i_ADDIU(&p, K1, K1, offsetof(struct kvm_vcpu, arch));
+
+	/* Save guest k0 into VCPU structure */
+	UASM_i_SW(&p, K0, offsetof(struct kvm_vcpu_arch, gprs[K0]), K1);
+
+	/* Branch to the common handler */
+	uasm_il_b(&p, &r, label_exit_common);
+	 uasm_i_nop(&p);
+
+	uasm_l_exit_common(&l, handler);
+	uasm_resolve_relocs(relocs, labels);
+
+	return p;
+}
+
+/**
+ * kvm_mips_build_exit() - Assemble common guest exit handler.
+ * @addr:	Address to start writing code.
+ *
+ * Assemble the generic guest exit handling code. This is called by the
+ * exception vectors (generated by kvm_mips_build_exception()), and calls
+ * kvm_mips_handle_exit(), then either resumes the guest or returns to the host
+ * depending on the return value.
+ *
+ * Returns:	Next address after end of written function.
+ */
+void *kvm_mips_build_exit(void *addr)
+{
+	u32 *p = addr;
+	unsigned int i;
+	struct uasm_label labels[3];
+	struct uasm_reloc relocs[3];
+	struct uasm_label *l = labels;
+	struct uasm_reloc *r = relocs;
+
+	memset(labels, 0, sizeof(labels));
+	memset(relocs, 0, sizeof(relocs));
+
+	/*
+	 * Generic Guest exception handler. We end up here when the guest
+	 * does something that causes a trap to kernel mode.
+	 *
+	 * Both k0/k1 registers will have already been saved (k0 into the vcpu
+	 * structure, and k1 into the scratch_tmp register).
+	 *
+	 * The k1 register will already contain the kvm_vcpu_arch pointer.
+	 */
+
+	/* Start saving Guest context to VCPU */
+	for (i = 0; i < 32; ++i) {
+		/* Guest k0/k1 saved later */
+		if (i == K0 || i == K1)
+			continue;
+		UASM_i_SW(&p, i, offsetof(struct kvm_vcpu_arch, gprs[i]), K1);
+	}
+
+#ifndef CONFIG_CPU_MIPSR6
+	/* We need to save hi/lo and restore them on the way out */
+	uasm_i_mfhi(&p, T0);
+	UASM_i_SW(&p, T0, offsetof(struct kvm_vcpu_arch, hi), K1);
+
+	uasm_i_mflo(&p, T0);
+	UASM_i_SW(&p, T0, offsetof(struct kvm_vcpu_arch, lo), K1);
+#endif
+
+	/* Finally save guest k1 to VCPU */
+	uasm_i_ehb(&p);
+	UASM_i_MFC0(&p, T0, scratch_tmp[0], scratch_tmp[1]);
+	UASM_i_SW(&p, T0, offsetof(struct kvm_vcpu_arch, gprs[K1]), K1);
+
+	/* Now that context has been saved, we can use other registers */
+
+	/* Restore vcpu */
+	UASM_i_MFC0(&p, A1, scratch_vcpu[0], scratch_vcpu[1]);
+	uasm_i_move(&p, S1, A1);
+
+	/* Restore run (vcpu->run) */
+	UASM_i_LW(&p, A0, offsetof(struct kvm_vcpu, run), A1);
+	/* Save pointer to run in s0, will be saved by the compiler */
+	uasm_i_move(&p, S0, A0);
+
+	/*
+	 * Save Host level EPC, BadVaddr and Cause to VCPU, useful to process
+	 * the exception
+	 */
+	UASM_i_MFC0(&p, K0, C0_EPC);
+	UASM_i_SW(&p, K0, offsetof(struct kvm_vcpu_arch, pc), K1);
+
+	UASM_i_MFC0(&p, K0, C0_BADVADDR);
+	UASM_i_SW(&p, K0, offsetof(struct kvm_vcpu_arch, host_cp0_badvaddr),
+		  K1);
+
+	uasm_i_mfc0(&p, K0, C0_CAUSE);
+	uasm_i_sw(&p, K0, offsetof(struct kvm_vcpu_arch, host_cp0_cause), K1);
+
+	/* Now restore the host state just enough to run the handlers */
+
+	/* Switch EBASE to the one used by Linux */
+	/* load up the host EBASE */
+	uasm_i_mfc0(&p, V0, C0_STATUS);
+
+	uasm_i_lui(&p, AT, ST0_BEV >> 16);
+	uasm_i_or(&p, K0, V0, AT);
+
+	uasm_i_mtc0(&p, K0, C0_STATUS);
+	uasm_i_ehb(&p);
+
+	UASM_i_LA_mostly(&p, K0, (long)&ebase);
+	UASM_i_LW(&p, K0, uasm_rel_lo((long)&ebase), K0);
+	build_set_exc_base(&p, K0);
+
+	if (raw_cpu_has_fpu) {
+		/*
+		 * If FPU is enabled, save FCR31 and clear it so that later
+		 * ctc1's don't trigger FPE for pending exceptions.
+		 */
+		uasm_i_lui(&p, AT, ST0_CU1 >> 16);
+		uasm_i_and(&p, V1, V0, AT);
+		uasm_il_beqz(&p, &r, V1, label_fpu_1);
+		 uasm_i_nop(&p);
+		uasm_i_cfc1(&p, T0, 31);
+		uasm_i_sw(&p, T0, offsetof(struct kvm_vcpu_arch, fpu.fcr31),
+			  K1);
+		uasm_i_ctc1(&p, ZERO, 31);
+		uasm_l_fpu_1(&l, p);
+	}
+
+	if (cpu_has_msa) {
+		/*
+		 * If MSA is enabled, save MSACSR and clear it so that later
+		 * instructions don't trigger MSAFPE for pending exceptions.
+		 */
+		uasm_i_mfc0(&p, T0, C0_CONFIG5);
+		uasm_i_ext(&p, T0, T0, 27, 1); /* MIPS_CONF5_MSAEN */
+		uasm_il_beqz(&p, &r, T0, label_msa_1);
+		 uasm_i_nop(&p);
+		uasm_i_cfcmsa(&p, T0, MSA_CSR);
+		uasm_i_sw(&p, T0, offsetof(struct kvm_vcpu_arch, fpu.msacsr),
+			  K1);
+		uasm_i_ctcmsa(&p, MSA_CSR, ZERO);
+		uasm_l_msa_1(&l, p);
+	}
+
+	/* Now that the new EBASE has been loaded, unset BEV and KSU_USER */
+	uasm_i_addiu(&p, AT, ZERO, ~(ST0_EXL | KSU_USER | ST0_IE));
+	uasm_i_and(&p, V0, V0, AT);
+	uasm_i_lui(&p, AT, ST0_CU0 >> 16);
+	uasm_i_or(&p, V0, V0, AT);
+	uasm_i_mtc0(&p, V0, C0_STATUS);
+	uasm_i_ehb(&p);
+
+	/* Load up host GP */
+	UASM_i_LW(&p, GP, offsetof(struct kvm_vcpu_arch, host_gp), K1);
+
+	/* Need a stack before we can jump to "C" */
+	UASM_i_LW(&p, SP, offsetof(struct kvm_vcpu_arch, host_stack), K1);
+
+	/* Saved host state */
+	UASM_i_ADDIU(&p, SP, SP, -(int)sizeof(struct pt_regs));
+
+	/*
+	 * XXXKYMA do we need to load the host ASID, maybe not because the
+	 * kernel entries are marked GLOBAL, need to verify
+	 */
+
+	/* Restore host scratch registers, as we'll have clobbered them */
+	kvm_mips_build_restore_scratch(&p, K0, SP);
+
+	/* Restore RDHWR access */
+	UASM_i_LA_mostly(&p, K0, (long)&hwrena);
+	uasm_i_lw(&p, K0, uasm_rel_lo((long)&hwrena), K0);
+	uasm_i_mtc0(&p, K0, C0_HWRENA);
+
+	/* Jump to handler */
+	/*
+	 * XXXKYMA: not sure if this is safe, how large is the stack??
+	 * Now jump to the kvm_mips_handle_exit() to see if we can deal
+	 * with this in the kernel
+	 */
+	UASM_i_LA(&p, T9, (unsigned long)kvm_mips_handle_exit);
+	uasm_i_jalr(&p, RA, T9);
+	 UASM_i_ADDIU(&p, SP, SP, -CALLFRAME_SIZ);
+
+	uasm_resolve_relocs(relocs, labels);
+
+	p = kvm_mips_build_ret_from_exit(p);
+
+	return p;
+}
+
+/**
+ * kvm_mips_build_ret_from_exit() - Assemble guest exit return handler.
+ * @addr:	Address to start writing code.
+ *
+ * Assemble the code to handle the return from kvm_mips_handle_exit(), either
+ * resuming the guest or returning to the host depending on the return value.
+ *
+ * Returns:	Next address after end of written function.
+ */
+static void *kvm_mips_build_ret_from_exit(void *addr)
+{
+	u32 *p = addr;
+	struct uasm_label labels[2];
+	struct uasm_reloc relocs[2];
+	struct uasm_label *l = labels;
+	struct uasm_reloc *r = relocs;
+
+	memset(labels, 0, sizeof(labels));
+	memset(relocs, 0, sizeof(relocs));
+
+	/* Return from handler Make sure interrupts are disabled */
+	uasm_i_di(&p, ZERO);
+	uasm_i_ehb(&p);
+
+	/*
+	 * XXXKYMA: k0/k1 could have been blown away if we processed
+	 * an exception while we were handling the exception from the
+	 * guest, reload k1
+	 */
+
+	uasm_i_move(&p, K1, S1);
+	UASM_i_ADDIU(&p, K1, K1, offsetof(struct kvm_vcpu, arch));
+
+	/*
+	 * Check return value, should tell us if we are returning to the
+	 * host (handle I/O etc)or resuming the guest
+	 */
+	uasm_i_andi(&p, T0, V0, RESUME_HOST);
+	uasm_il_bnez(&p, &r, T0, label_return_to_host);
+	 uasm_i_nop(&p);
+
+	p = kvm_mips_build_ret_to_guest(p);
+
+	uasm_l_return_to_host(&l, p);
+	p = kvm_mips_build_ret_to_host(p);
+
+	uasm_resolve_relocs(relocs, labels);
+
+	return p;
+}
+
+/**
+ * kvm_mips_build_ret_to_guest() - Assemble code to return to the guest.
+ * @addr:	Address to start writing code.
+ *
+ * Assemble the code to handle return from the guest exit handler
+ * (kvm_mips_handle_exit()) back to the guest.
+ *
+ * Returns:	Next address after end of written function.
+ */
+static void *kvm_mips_build_ret_to_guest(void *addr)
+{
+	u32 *p = addr;
+
+	/* Put the saved pointer to vcpu (s1) back into the scratch register */
+	UASM_i_MTC0(&p, S1, scratch_vcpu[0], scratch_vcpu[1]);
+
+	/* Load up the Guest EBASE to minimize the window where BEV is set */
+	UASM_i_LW(&p, T0, offsetof(struct kvm_vcpu_arch, guest_ebase), K1);
+
+	/* Switch EBASE back to the one used by KVM */
+	uasm_i_mfc0(&p, V1, C0_STATUS);
+	uasm_i_lui(&p, AT, ST0_BEV >> 16);
+	uasm_i_or(&p, K0, V1, AT);
+	uasm_i_mtc0(&p, K0, C0_STATUS);
+	uasm_i_ehb(&p);
+	build_set_exc_base(&p, T0);
+
+	/* Setup status register for running guest in UM */
+	uasm_i_ori(&p, V1, V1, ST0_EXL | KSU_USER | ST0_IE);
+	UASM_i_LA(&p, AT, ~(ST0_CU0 | ST0_MX));
+	uasm_i_and(&p, V1, V1, AT);
+	uasm_i_mtc0(&p, V1, C0_STATUS);
+	uasm_i_ehb(&p);
+
+	p = kvm_mips_build_enter_guest(p);
+
+	return p;
+}
+
+/**
+ * kvm_mips_build_ret_to_host() - Assemble code to return to the host.
+ * @addr:	Address to start writing code.
+ *
+ * Assemble the code to handle return from the guest exit handler
+ * (kvm_mips_handle_exit()) back to the host, i.e. to the caller of the vcpu_run
+ * function generated by kvm_mips_build_vcpu_run().
+ *
+ * Returns:	Next address after end of written function.
+ */
+static void *kvm_mips_build_ret_to_host(void *addr)
+{
+	u32 *p = addr;
+	unsigned int i;
+
+	/* EBASE is already pointing to Linux */
+	UASM_i_LW(&p, K1, offsetof(struct kvm_vcpu_arch, host_stack), K1);
+	UASM_i_ADDIU(&p, K1, K1, -(int)sizeof(struct pt_regs));
+
+	/*
+	 * r2/v0 is the return code, shift it down by 2 (arithmetic)
+	 * to recover the err code
+	 */
+	uasm_i_sra(&p, K0, V0, 2);
+	uasm_i_move(&p, V0, K0);
+
+	/* Load context saved on the host stack */
+	for (i = 16; i < 31; ++i) {
+		if (i == 24)
+			i = 28;
+		UASM_i_LW(&p, i, offsetof(struct pt_regs, regs[i]), K1);
+	}
+
+	/* Restore RDHWR access */
+	UASM_i_LA_mostly(&p, K0, (long)&hwrena);
+	uasm_i_lw(&p, K0, uasm_rel_lo((long)&hwrena), K0);
+	uasm_i_mtc0(&p, K0, C0_HWRENA);
+
+	/* Restore RA, which is the address we will return to */
+	UASM_i_LW(&p, RA, offsetof(struct pt_regs, regs[RA]), K1);
+	uasm_i_jr(&p, RA);
+	 uasm_i_nop(&p);
+
+	return p;
+}
+