/*
 * 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 <linux/log2.h>
#include <asm/mmu_context.h>
#include <asm/msa.h>
#include <asm/setup.h>
#include <asm/tlbex.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_PWBASE       5, 5
#define C0_HWRENA       7, 0
#define C0_BADVADDR     8, 0
#define C0_BADINSTR     8, 1
#define C0_BADINSTRP    8, 2
#define C0_PGD          9, 7
#define C0_ENTRYHI      10, 0
#define C0_GUESTCTL1    10, 4
#define C0_STATUS       12, 0
#define C0_GUESTCTL0    12, 6
#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);

/*
 * The version of this function in tlbex.c uses current_cpu_type(), but for KVM
 * we assume symmetry.
 */
static int c0_kscratch(void)
{
        switch (boot_cpu_type()) {
        case CPU_XLP:
        case CPU_XLR:
                return 22;
        default:
                return 31;
        }
}

/**
 * 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;

        if (pgd_reg != -1)
                kscratch_mask &= ~BIT(pgd_reg);

        /* Pick a scratch register for storing VCPU */
        if (kscratch_mask) {
                scratch_vcpu[0] = c0_kscratch();
                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] = c0_kscratch();
                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] == c0_kscratch()) {
                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] == c0_kscratch()) {
                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_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: 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, A0, scratch_vcpu[0], scratch_vcpu[1]);

        /* Offset into vcpu->arch */
        UASM_i_ADDIU(&p, K1, A0, 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 __maybe_unused *l = labels;
        struct uasm_reloc __maybe_unused *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);

        /* Save normal linux process pgd (VZ guarantees pgd_reg is set) */
        if (cpu_has_ldpte)
                UASM_i_MFC0(&p, K0, C0_PWBASE);
        else
                UASM_i_MFC0(&p, K0, c0_kscratch(), pgd_reg);
        UASM_i_SW(&p, K0, offsetof(struct kvm_vcpu_arch, host_pgd), K1);

        /*
         * Set up KVM GPA pgd.
         * This does roughly the same as TLBMISS_HANDLER_SETUP_PGD():
         * - call tlbmiss_handler_setup_pgd(mm->pgd)
         * - write mm->pgd into CP0_PWBase
         *
         * We keep S0 pointing at struct kvm so we can load the ASID below.
         */
        UASM_i_LW(&p, S0, (int)offsetof(struct kvm_vcpu, kvm) -
                          (int)offsetof(struct kvm_vcpu, arch), K1);
        UASM_i_LW(&p, A0, offsetof(struct kvm, arch.gpa_mm.pgd), S0);
        UASM_i_LA(&p, T9, (unsigned long)tlbmiss_handler_setup_pgd);
        uasm_i_jalr(&p, RA, T9);
        /* delay slot */
        if (cpu_has_htw)
                UASM_i_MTC0(&p, A0, C0_PWBASE);
        else
                uasm_i_nop(&p);

        /* Set GM bit to setup eret to VZ guest context */
        uasm_i_addiu(&p, V1, ZERO, 1);
        uasm_i_mfc0(&p, K0, C0_GUESTCTL0);
        uasm_i_ins(&p, K0, V1, MIPS_GCTL0_GM_SHIFT, 1);
        uasm_i_mtc0(&p, K0, C0_GUESTCTL0);

        if (cpu_has_guestid) {
                /*
                 * Set root mode GuestID, so that root TLB refill handler can
                 * use the correct GuestID in the root TLB.
                 */

                /* Get current GuestID */
                uasm_i_mfc0(&p, T0, C0_GUESTCTL1);
                /* Set GuestCtl1.RID = GuestCtl1.ID */
                uasm_i_ext(&p, T1, T0, MIPS_GCTL1_ID_SHIFT,
                           MIPS_GCTL1_ID_WIDTH);
                uasm_i_ins(&p, T0, T1, MIPS_GCTL1_RID_SHIFT,
                           MIPS_GCTL1_RID_WIDTH);
                uasm_i_mtc0(&p, T0, C0_GUESTCTL1);

                /* GuestID handles dealiasing so we don't need to touch ASID */
                goto skip_asid_restore;
        }

        /* Root ASID Dealias (RAD) */

        /* Save host ASID */
        UASM_i_MFC0(&p, K0, C0_ENTRYHI);
        UASM_i_SW(&p, K0, offsetof(struct kvm_vcpu_arch, host_entryhi),
                  K1);

        /* Set the root ASID for the Guest */
        UASM_i_ADDIU(&p, T1, S0,
                     offsetof(struct kvm, arch.gpa_mm.context.asid));

        /* 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);
        /* index the ASID array */
        uasm_i_sll(&p, T2, T2, ilog2(sizeof(long)));
        UASM_i_ADDU(&p, T3, T1, T2);
        UASM_i_LW(&p, K0, 0, T3);
#ifdef CONFIG_MIPS_ASID_BITS_VARIABLE
        /*
         * reuse ASID array offset
         * cpuinfo_mips is a multiple of sizeof(long)
         */
        uasm_i_addiu(&p, T3, ZERO, sizeof(struct cpuinfo_mips)/sizeof(long));
        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

        /* Set up KVM VZ root ASID (!guestid) */
        uasm_i_mtc0(&p, K0, C0_ENTRYHI);
skip_asid_restore:
        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_tlb_refill_exception() - Assemble TLB refill handler.
 * @addr:       Address to start writing code.
 * @handler:    Address of common handler (within range of @addr).
 *
 * Assemble TLB refill exception fast path handler for guest execution.
 *
 * Returns:     Next address after end of written function.
 */
void *kvm_mips_build_tlb_refill_exception(void *addr, void *handler)
{
        u32 *p = addr;
        struct uasm_label labels[2];
        struct uasm_reloc relocs[2];
#ifndef CONFIG_CPU_LOONGSON64
        struct uasm_label *l = labels;
        struct uasm_reloc *r = relocs;
#endif

        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]);

        /* Save guest k0 into VCPU structure */
        UASM_i_SW(&p, K0, offsetof(struct kvm_vcpu, arch.gprs[K0]), K1);

        /*
         * Some of the common tlbex code uses current_cpu_type(). For KVM we
         * assume symmetry and just disable preemption to silence the warning.
         */
        preempt_disable();

#ifdef CONFIG_CPU_LOONGSON64
        UASM_i_MFC0(&p, K1, C0_PGD);
        uasm_i_lddir(&p, K0, K1, 3);  /* global page dir */
#ifndef __PAGETABLE_PMD_FOLDED
        uasm_i_lddir(&p, K1, K0, 1);  /* middle page dir */
#endif
        uasm_i_ldpte(&p, K1, 0);      /* even */
        uasm_i_ldpte(&p, K1, 1);      /* odd */
        uasm_i_tlbwr(&p);
#else
        /*
         * Now for the actual refill bit. A lot of this can be common with the
         * Linux TLB refill handler, however we don't need to handle so many
         * cases. We only need to handle user mode refills, and user mode runs
         * with 32-bit addressing.
         *
         * Therefore the branch to label_vmalloc generated by build_get_pmde64()
         * that isn't resolved should never actually get taken and is harmless
         * to leave in place for now.
         */

#ifdef CONFIG_64BIT
        build_get_pmde64(&p, &l, &r, K0, K1); /* get pmd in K1 */
#else
        build_get_pgde32(&p, K0, K1); /* get pgd in K1 */
#endif

        /* we don't support huge pages yet */

        build_get_ptep(&p, K0, K1);
        build_update_entries(&p, K0, K1);
        build_tlb_write_entry(&p, &l, &r, tlb_random);
#endif

        preempt_enable();

        /* Get the VCPU pointer from the VCPU scratch register again */
        UASM_i_MFC0(&p, K1, scratch_vcpu[0], scratch_vcpu[1]);

        /* Restore the guest's k0/k1 registers */
        UASM_i_LW(&p, K0, offsetof(struct kvm_vcpu, arch.gprs[K0]), K1);
        uasm_i_ehb(&p);
        UASM_i_MFC0(&p, K1, scratch_tmp[0], scratch_tmp[1]);

        /* Jump to guest */
        uasm_i_eret(&p);

        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, S0, scratch_vcpu[0], scratch_vcpu[1]);

        /*
         * 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);

        if (cpu_has_badinstr) {
                uasm_i_mfc0(&p, K0, C0_BADINSTR);
                uasm_i_sw(&p, K0, offsetof(struct kvm_vcpu_arch,
                                           host_cp0_badinstr), K1);
        }

        if (cpu_has_badinstrp) {
                uasm_i_mfc0(&p, K0, C0_BADINSTRP);
                uasm_i_sw(&p, K0, offsetof(struct kvm_vcpu_arch,
                                           host_cp0_badinstrp), 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);
        }

        /* Restore host ASID */
        if (!cpu_has_guestid) {
                UASM_i_LW(&p, K0, offsetof(struct kvm_vcpu_arch, host_entryhi),
                          K1);
                UASM_i_MTC0(&p, K0, C0_ENTRYHI);
        }

        /*
         * Set up normal Linux process pgd.
         * This does roughly the same as TLBMISS_HANDLER_SETUP_PGD():
         * - call tlbmiss_handler_setup_pgd(mm->pgd)
         * - write mm->pgd into CP0_PWBase
         */
        UASM_i_LW(&p, A0,
                  offsetof(struct kvm_vcpu_arch, host_pgd), K1);
        UASM_i_LA(&p, T9, (unsigned long)tlbmiss_handler_setup_pgd);
        uasm_i_jalr(&p, RA, T9);
        /* delay slot */
        if (cpu_has_htw)
                UASM_i_MTC0(&p, A0, C0_PWBASE);
        else
                uasm_i_nop(&p);

        /* Clear GM bit so we don't enter guest mode when EXL is cleared */
        uasm_i_mfc0(&p, K0, C0_GUESTCTL0);
        uasm_i_ins(&p, K0, ZERO, MIPS_GCTL0_GM_SHIFT, 1);
        uasm_i_mtc0(&p, K0, C0_GUESTCTL0);

        /* Save GuestCtl0 so we can access GExcCode after CPU migration */
        uasm_i_sw(&p, K0,
                  offsetof(struct kvm_vcpu_arch, host_cp0_guestctl0), K1);

        if (cpu_has_guestid) {
                /*
                 * Clear root mode GuestID, so that root TLB operations use the
                 * root GuestID in the root TLB.
                 */
                uasm_i_mfc0(&p, T0, C0_GUESTCTL1);
                /* Set GuestCtl1.RID = MIPS_GCTL1_ROOT_GUESTID (i.e. 0) */
                uasm_i_ins(&p, T0, ZERO, MIPS_GCTL1_RID_SHIFT,
                           MIPS_GCTL1_RID_WIDTH);
                uasm_i_mtc0(&p, T0, C0_GUESTCTL1);
        }

        /* 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);
#ifdef CONFIG_64BIT
        uasm_i_ori(&p, V0, V0, ST0_SX | ST0_UX);
#endif
        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_move(&p, A0, S0);
        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, S0);
        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 (s0) back into the scratch register */
        UASM_i_MTC0(&p, S0, 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 | ST0_SX | ST0_UX));
        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;
}