Merge tag 'trace-printf-v6.13' of git://git.kernel.org/pub/scm/linux/kernel/git/trace...

[drm/drm-misc.git] / arch / arc / mm / tlb.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * TLB Management (flush/create/diagnostics) for MMUv3 and MMUv4
 *
 * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
 *
 */

#include <linux/module.h>
#include <linux/bug.h>
#include <linux/mm_types.h>

#include <asm/arcregs.h>
#include <asm/setup.h>
#include <asm/mmu_context.h>
#include <asm/mmu.h>

/* A copy of the ASID from the PID reg is kept in asid_cache */
DEFINE_PER_CPU(unsigned int, asid_cache) = MM_CTXT_FIRST_CYCLE;

static struct cpuinfo_arc_mmu {
        unsigned int ver, pg_sz_k, s_pg_sz_m, pae, sets, ways;
} mmuinfo;

/*
 * Utility Routine to erase a J-TLB entry
 * Caller needs to setup Index Reg (manually or via getIndex)
 */
static inline void __tlb_entry_erase(void)
{
        write_aux_reg(ARC_REG_TLBPD1, 0);

        if (is_pae40_enabled())
                write_aux_reg(ARC_REG_TLBPD1HI, 0);

        write_aux_reg(ARC_REG_TLBPD0, 0);
        write_aux_reg(ARC_REG_TLBCOMMAND, TLBWrite);
}

static void utlb_invalidate(void)
{
        write_aux_reg(ARC_REG_TLBCOMMAND, TLBIVUTLB);
}

#ifdef CONFIG_ARC_MMU_V3

static inline unsigned int tlb_entry_lkup(unsigned long vaddr_n_asid)
{
        unsigned int idx;

        write_aux_reg(ARC_REG_TLBPD0, vaddr_n_asid);

        write_aux_reg(ARC_REG_TLBCOMMAND, TLBProbe);
        idx = read_aux_reg(ARC_REG_TLBINDEX);

        return idx;
}

static void tlb_entry_erase(unsigned int vaddr_n_asid)
{
        unsigned int idx;

        /* Locate the TLB entry for this vaddr + ASID */
        idx = tlb_entry_lkup(vaddr_n_asid);

        /* No error means entry found, zero it out */
        if (likely(!(idx & TLB_LKUP_ERR))) {
                __tlb_entry_erase();
        } else {
                /* Duplicate entry error */
                WARN(idx == TLB_DUP_ERR, "Probe returned Dup PD for %x\n",
                                           vaddr_n_asid);
        }
}

static void tlb_entry_insert(unsigned int pd0, phys_addr_t pd1)
{
        unsigned int idx;

        /*
         * First verify if entry for this vaddr+ASID already exists
         * This also sets up PD0 (vaddr, ASID..) for final commit
         */
        idx = tlb_entry_lkup(pd0);

        /*
         * If Not already present get a free slot from MMU.
         * Otherwise, Probe would have located the entry and set INDEX Reg
         * with existing location. This will cause Write CMD to over-write
         * existing entry with new PD0 and PD1
         */
        if (likely(idx & TLB_LKUP_ERR))
                write_aux_reg(ARC_REG_TLBCOMMAND, TLBGetIndex);

        /* setup the other half of TLB entry (pfn, rwx..) */
        write_aux_reg(ARC_REG_TLBPD1, pd1);

        /*
         * Commit the Entry to MMU
         * It doesn't sound safe to use the TLBWriteNI cmd here
         * which doesn't flush uTLBs. I'd rather be safe than sorry.
         */
        write_aux_reg(ARC_REG_TLBCOMMAND, TLBWrite);
}

#else   /* MMUv4 */

static void tlb_entry_erase(unsigned int vaddr_n_asid)
{
        write_aux_reg(ARC_REG_TLBPD0, vaddr_n_asid | _PAGE_PRESENT);
        write_aux_reg(ARC_REG_TLBCOMMAND, TLBDeleteEntry);
}

static void tlb_entry_insert(unsigned int pd0, phys_addr_t pd1)
{
        write_aux_reg(ARC_REG_TLBPD0, pd0);

        if (!is_pae40_enabled()) {
                write_aux_reg(ARC_REG_TLBPD1, pd1);
        } else {
                write_aux_reg(ARC_REG_TLBPD1, pd1 & 0xFFFFFFFF);
                write_aux_reg(ARC_REG_TLBPD1HI, (u64)pd1 >> 32);
        }

        write_aux_reg(ARC_REG_TLBCOMMAND, TLBInsertEntry);
}

#endif

/*
 * Un-conditionally (without lookup) erase the entire MMU contents
 */

noinline void local_flush_tlb_all(void)
{
        struct cpuinfo_arc_mmu *mmu = &mmuinfo;
        unsigned long flags;
        unsigned int entry;
        int num_tlb = mmu->sets * mmu->ways;

        local_irq_save(flags);

        /* Load PD0 and PD1 with template for a Blank Entry */
        write_aux_reg(ARC_REG_TLBPD1, 0);

        if (is_pae40_enabled())
                write_aux_reg(ARC_REG_TLBPD1HI, 0);

        write_aux_reg(ARC_REG_TLBPD0, 0);

        for (entry = 0; entry < num_tlb; entry++) {
                /* write this entry to the TLB */
                write_aux_reg(ARC_REG_TLBINDEX, entry);
                write_aux_reg(ARC_REG_TLBCOMMAND, TLBWriteNI);
        }

        if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
                const int stlb_idx = 0x800;

                /* Blank sTLB entry */
                write_aux_reg(ARC_REG_TLBPD0, _PAGE_HW_SZ);

                for (entry = stlb_idx; entry < stlb_idx + 16; entry++) {
                        write_aux_reg(ARC_REG_TLBINDEX, entry);
                        write_aux_reg(ARC_REG_TLBCOMMAND, TLBWriteNI);
                }
        }

        utlb_invalidate();

        local_irq_restore(flags);
}

/*
 * Flush the entire MM for userland. The fastest way is to move to Next ASID
 */
noinline void local_flush_tlb_mm(struct mm_struct *mm)
{
        /*
         * Small optimisation courtesy IA64
         * flush_mm called during fork,exit,munmap etc, multiple times as well.
         * Only for fork( ) do we need to move parent to a new MMU ctxt,
         * all other cases are NOPs, hence this check.
         */
        if (atomic_read(&mm->mm_users) == 0)
                return;

        /*
         * - Move to a new ASID, but only if the mm is still wired in
         *   (Android Binder ended up calling this for vma->mm != tsk->mm,
         *    causing h/w - s/w ASID to get out of sync)
         * - Also get_new_mmu_context() new implementation allocates a new
         *   ASID only if it is not allocated already - so unallocate first
         */
        destroy_context(mm);
        if (current->mm == mm)
                get_new_mmu_context(mm);
}

/*
 * Flush a Range of TLB entries for userland.
 * @start is inclusive, while @end is exclusive
 * Difference between this and Kernel Range Flush is
 *  -Here the fastest way (if range is too large) is to move to next ASID
 *      without doing any explicit Shootdown
 *  -In case of kernel Flush, entry has to be shot down explicitly
 */
void local_flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
                           unsigned long end)
{
        const unsigned int cpu = smp_processor_id();
        unsigned long flags;

        /* If range @start to @end is more than 32 TLB entries deep,
         * it's better to move to a new ASID rather than searching for
         * individual entries and then shooting them down
         *
         * The calc above is rough, doesn't account for unaligned parts,
         * since this is heuristics based anyways
         */
        if (unlikely((end - start) >= PAGE_SIZE * 32)) {
                local_flush_tlb_mm(vma->vm_mm);
                return;
        }

        /*
         * @start moved to page start: this alone suffices for checking
         * loop end condition below, w/o need for aligning @end to end
         * e.g. 2000 to 4001 will anyhow loop twice
         */
        start &= PAGE_MASK;

        local_irq_save(flags);

        if (asid_mm(vma->vm_mm, cpu) != MM_CTXT_NO_ASID) {
                while (start < end) {
                        tlb_entry_erase(start | hw_pid(vma->vm_mm, cpu));
                        start += PAGE_SIZE;
                }
        }

        local_irq_restore(flags);
}

/* Flush the kernel TLB entries - vmalloc/modules (Global from MMU perspective)
 *  @start, @end interpreted as kvaddr
 * Interestingly, shared TLB entries can also be flushed using just
 * @start,@end alone (interpreted as user vaddr), although technically SASID
 * is also needed. However our smart TLbProbe lookup takes care of that.
 */
void local_flush_tlb_kernel_range(unsigned long start, unsigned long end)
{
        unsigned long flags;

        /* exactly same as above, except for TLB entry not taking ASID */

        if (unlikely((end - start) >= PAGE_SIZE * 32)) {
                local_flush_tlb_all();
                return;
        }

        start &= PAGE_MASK;

        local_irq_save(flags);
        while (start < end) {
                tlb_entry_erase(start);
                start += PAGE_SIZE;
        }

        local_irq_restore(flags);
}

/*
 * Delete TLB entry in MMU for a given page (??? address)
 * NOTE One TLB entry contains translation for single PAGE
 */

void local_flush_tlb_page(struct vm_area_struct *vma, unsigned long page)
{
        const unsigned int cpu = smp_processor_id();
        unsigned long flags;

        /* Note that it is critical that interrupts are DISABLED between
         * checking the ASID and using it flush the TLB entry
         */
        local_irq_save(flags);

        if (asid_mm(vma->vm_mm, cpu) != MM_CTXT_NO_ASID) {
                tlb_entry_erase((page & PAGE_MASK) | hw_pid(vma->vm_mm, cpu));
        }

        local_irq_restore(flags);
}

#ifdef CONFIG_SMP

struct tlb_args {
        struct vm_area_struct *ta_vma;
        unsigned long ta_start;
        unsigned long ta_end;
};

static inline void ipi_flush_tlb_page(void *arg)
{
        struct tlb_args *ta = arg;

        local_flush_tlb_page(ta->ta_vma, ta->ta_start);
}

static inline void ipi_flush_tlb_range(void *arg)
{
        struct tlb_args *ta = arg;

        local_flush_tlb_range(ta->ta_vma, ta->ta_start, ta->ta_end);
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
static inline void ipi_flush_pmd_tlb_range(void *arg)
{
        struct tlb_args *ta = arg;

        local_flush_pmd_tlb_range(ta->ta_vma, ta->ta_start, ta->ta_end);
}
#endif

static inline void ipi_flush_tlb_kernel_range(void *arg)
{
        struct tlb_args *ta = (struct tlb_args *)arg;

        local_flush_tlb_kernel_range(ta->ta_start, ta->ta_end);
}

void flush_tlb_all(void)
{
        on_each_cpu((smp_call_func_t)local_flush_tlb_all, NULL, 1);
}

void flush_tlb_mm(struct mm_struct *mm)
{
        on_each_cpu_mask(mm_cpumask(mm), (smp_call_func_t)local_flush_tlb_mm,
                         mm, 1);
}

void flush_tlb_page(struct vm_area_struct *vma, unsigned long uaddr)
{
        struct tlb_args ta = {
                .ta_vma = vma,
                .ta_start = uaddr
        };

        on_each_cpu_mask(mm_cpumask(vma->vm_mm), ipi_flush_tlb_page, &ta, 1);
}

void flush_tlb_range(struct vm_area_struct *vma, unsigned long start,
                     unsigned long end)
{
        struct tlb_args ta = {
                .ta_vma = vma,
                .ta_start = start,
                .ta_end = end
        };

        on_each_cpu_mask(mm_cpumask(vma->vm_mm), ipi_flush_tlb_range, &ta, 1);
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
void flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
                         unsigned long end)
{
        struct tlb_args ta = {
                .ta_vma = vma,
                .ta_start = start,
                .ta_end = end
        };

        on_each_cpu_mask(mm_cpumask(vma->vm_mm), ipi_flush_pmd_tlb_range, &ta, 1);
}
#endif

void flush_tlb_kernel_range(unsigned long start, unsigned long end)
{
        struct tlb_args ta = {
                .ta_start = start,
                .ta_end = end
        };

        on_each_cpu(ipi_flush_tlb_kernel_range, &ta, 1);
}
#endif

/*
 * Routine to create a TLB entry
 */
static void create_tlb(struct vm_area_struct *vma, unsigned long vaddr, pte_t *ptep)
{
        unsigned long flags;
        unsigned int asid_or_sasid, rwx;
        unsigned long pd0;
        phys_addr_t pd1;

        /*
         * create_tlb() assumes that current->mm == vma->mm, since
         * -it ASID for TLB entry is fetched from MMU ASID reg (valid for curr)
         * -completes the lazy write to SASID reg (again valid for curr tsk)
         *
         * Removing the assumption involves
         * -Using vma->mm->context{ASID,SASID}, as opposed to MMU reg.
         * -More importantly it makes this handler inconsistent with fast-path
         *  TLB Refill handler which always deals with "current"
         *
         * Let's see the use cases when current->mm != vma->mm and we land here
         *  1. execve->copy_strings()->__get_user_pages->handle_mm_fault
         *     Here VM wants to pre-install a TLB entry for user stack while
         *     current->mm still points to pre-execve mm (hence the condition).
         *     However the stack vaddr is soon relocated (randomization) and
         *     move_page_tables() tries to undo that TLB entry.
         *     Thus not creating TLB entry is not any worse.
         *
         *  2. ptrace(POKETEXT) causes a CoW - debugger(current) inserting a
         *     breakpoint in debugged task. Not creating a TLB now is not
         *     performance critical.
         *
         * Both the cases above are not good enough for code churn.
         */
        if (current->active_mm != vma->vm_mm)
                return;

        local_irq_save(flags);

        vaddr &= PAGE_MASK;

        /* update this PTE credentials */
        pte_val(*ptep) |= (_PAGE_PRESENT | _PAGE_ACCESSED);

        /* Create HW TLB(PD0,PD1) from PTE  */

        /* ASID for this task */
        asid_or_sasid = read_aux_reg(ARC_REG_PID) & 0xff;

        pd0 = vaddr | asid_or_sasid | (pte_val(*ptep) & PTE_BITS_IN_PD0);

        /*
         * ARC MMU provides fully orthogonal access bits for K/U mode,
         * however Linux only saves 1 set to save PTE real-estate
         * Here we convert 3 PTE bits into 6 MMU bits:
         * -Kernel only entries have Kr Kw Kx 0 0 0
         * -User entries have mirrored K and U bits
         */
        rwx = pte_val(*ptep) & PTE_BITS_RWX;

        if (pte_val(*ptep) & _PAGE_GLOBAL)
                rwx <<= 3;              /* r w x => Kr Kw Kx 0 0 0 */
        else
                rwx |= (rwx << 3);      /* r w x => Kr Kw Kx Ur Uw Ux */

        pd1 = rwx | (pte_val(*ptep) & PTE_BITS_NON_RWX_IN_PD1);

        tlb_entry_insert(pd0, pd1);

        local_irq_restore(flags);
}

/*
 * Called at the end of pagefault, for a userspace mapped page
 *  -pre-install the corresponding TLB entry into MMU
 *  -Finalize the delayed D-cache flush of kernel mapping of page due to
 *      flush_dcache_page(), copy_user_page()
 *
 * Note that flush (when done) involves both WBACK - so physical page is
 * in sync as well as INV - so any non-congruent aliases don't remain
 */
void update_mmu_cache_range(struct vm_fault *vmf, struct vm_area_struct *vma,
                unsigned long vaddr_unaligned, pte_t *ptep, unsigned int nr)
{
        unsigned long vaddr = vaddr_unaligned & PAGE_MASK;
        phys_addr_t paddr = pte_val(*ptep) & PAGE_MASK_PHYS;
        struct page *page = pfn_to_page(pte_pfn(*ptep));

        create_tlb(vma, vaddr, ptep);

        if (page == ZERO_PAGE(0))
                return;

        /*
         * For executable pages, since icache doesn't snoop dcache, any
         * dirty K-mapping of a code page needs to be wback+inv so that
         * icache fetch by userspace sees code correctly.
         */
        if (vma->vm_flags & VM_EXEC) {
                struct folio *folio = page_folio(page);
                int dirty = !test_and_set_bit(PG_dc_clean, &folio->flags);
                if (dirty) {
                        unsigned long offset = offset_in_folio(folio, paddr);
                        nr = folio_nr_pages(folio);
                        paddr -= offset;
                        vaddr -= offset;
                        /* wback + inv dcache lines (K-mapping) */
                        __flush_dcache_pages(paddr, paddr, nr);

                        /* invalidate any existing icache lines (U-mapping) */
                        if (vma->vm_flags & VM_EXEC)
                                __inv_icache_pages(paddr, vaddr, nr);
                }
        }
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

/*
 * MMUv4 in HS38x cores supports Super Pages which are basis for Linux THP
 * support.
 *
 * Normal and Super pages can co-exist (ofcourse not overlap) in TLB with a
 * new bit "SZ" in TLB page descriptor to distinguish between them.
 * Super Page size is configurable in hardware (4K to 16M), but fixed once
 * RTL builds.
 *
 * The exact THP size a Linux configuration will support is a function of:
 *  - MMU page size (typical 8K, RTL fixed)
 *  - software page walker address split between PGD:PTE:PFN (typical
 *    11:8:13, but can be changed with 1 line)
 * So for above default, THP size supported is 8K * (2^8) = 2M
 *
 * Default Page Walker is 2 levels, PGD:PTE:PFN, which in THP regime
 * reduces to 1 level (as PTE is folded into PGD and canonically referred
 * to as PMD).
 * Thus THP PMD accessors are implemented in terms of PTE (just like sparc)
 */

void update_mmu_cache_pmd(struct vm_area_struct *vma, unsigned long addr,
                                 pmd_t *pmd)
{
        pte_t pte = __pte(pmd_val(*pmd));
        update_mmu_cache_range(NULL, vma, addr, &pte, HPAGE_PMD_NR);
}

void local_flush_pmd_tlb_range(struct vm_area_struct *vma, unsigned long start,
                               unsigned long end)
{
        unsigned int cpu;
        unsigned long flags;

        local_irq_save(flags);

        cpu = smp_processor_id();

        if (likely(asid_mm(vma->vm_mm, cpu) != MM_CTXT_NO_ASID)) {
                unsigned int asid = hw_pid(vma->vm_mm, cpu);

                /* No need to loop here: this will always be for 1 Huge Page */
                tlb_entry_erase(start | _PAGE_HW_SZ | asid);
        }

        local_irq_restore(flags);
}

#endif

/* Read the Cache Build Configuration Registers, Decode them and save into
 * the cpuinfo structure for later use.
 * No Validation is done here, simply read/convert the BCRs
 */
int arc_mmu_mumbojumbo(int c, char *buf, int len)
{
        struct cpuinfo_arc_mmu *mmu = &mmuinfo;
        unsigned int bcr, u_dtlb, u_itlb, sasid;
        struct bcr_mmu_3 *mmu3;
        struct bcr_mmu_4 *mmu4;
        char super_pg[64] = "";
        int n = 0;

        bcr = read_aux_reg(ARC_REG_MMU_BCR);
        mmu->ver = (bcr >> 24);

        if (is_isa_arcompact() && mmu->ver == 3) {
                mmu3 = (struct bcr_mmu_3 *)&bcr;
                mmu->pg_sz_k = 1 << (mmu3->pg_sz - 1);
                mmu->sets = 1 << mmu3->sets;
                mmu->ways = 1 << mmu3->ways;
                u_dtlb = mmu3->u_dtlb;
                u_itlb = mmu3->u_itlb;
                sasid = mmu3->sasid;
        } else {
                mmu4 = (struct bcr_mmu_4 *)&bcr;
                mmu->pg_sz_k = 1 << (mmu4->sz0 - 1);
                mmu->s_pg_sz_m = 1 << (mmu4->sz1 - 11);
                mmu->sets = 64 << mmu4->n_entry;
                mmu->ways = mmu4->n_ways * 2;
                u_dtlb = mmu4->u_dtlb * 4;
                u_itlb = mmu4->u_itlb * 4;
                sasid = mmu4->sasid;
                mmu->pae = mmu4->pae;
        }

        if (mmu->s_pg_sz_m)
                scnprintf(super_pg, 64, "/%dM%s",
                          mmu->s_pg_sz_m,
                          IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) ? " (THP enabled)":"");

        n += scnprintf(buf + n, len - n,
                      "MMU [v%x]\t: %dk%s, swalk %d lvl, JTLB %dx%d, uDTLB %d, uITLB %d%s%s%s\n",
                       mmu->ver, mmu->pg_sz_k, super_pg, CONFIG_PGTABLE_LEVELS,
                       mmu->sets, mmu->ways,
                       u_dtlb, u_itlb,
                       IS_AVAIL1(sasid, ", SASID"),
                       IS_AVAIL2(mmu->pae, ", PAE40 ", CONFIG_ARC_HAS_PAE40));

        return n;
}

int pae40_exist_but_not_enab(void)
{
        return mmuinfo.pae && !is_pae40_enabled();
}

void arc_mmu_init(void)
{
        struct cpuinfo_arc_mmu *mmu = &mmuinfo;
        int compat = 0;

        /*
         * Can't be done in processor.h due to header include dependencies
         */
        BUILD_BUG_ON(!IS_ALIGNED((CONFIG_ARC_KVADDR_SIZE << 20), PMD_SIZE));

        /*
         * stack top size sanity check,
         * Can't be done in processor.h due to header include dependencies
         */
        BUILD_BUG_ON(!IS_ALIGNED(STACK_TOP, PMD_SIZE));

        /*
         * Ensure that MMU features assumed by kernel exist in hardware.
         *  - For older ARC700 cpus, only v3 supported
         *  - For HS cpus, v4 was baseline and v5 is backwards compatible
         *    (will run older software).
         */
        if (is_isa_arcompact() && mmu->ver == 3)
                compat = 1;
        else if (is_isa_arcv2() && mmu->ver >= 4)
                compat = 1;

        if (!compat)
                panic("MMU ver %d doesn't match kernel built for\n", mmu->ver);

        if (mmu->pg_sz_k != TO_KB(PAGE_SIZE))
                panic("MMU pg size != PAGE_SIZE (%luk)\n", TO_KB(PAGE_SIZE));

        if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) &&
            mmu->s_pg_sz_m != TO_MB(HPAGE_PMD_SIZE))
                panic("MMU Super pg size != Linux HPAGE_PMD_SIZE (%luM)\n",
                      (unsigned long)TO_MB(HPAGE_PMD_SIZE));

        if (IS_ENABLED(CONFIG_ARC_HAS_PAE40) && !mmu->pae)
                panic("Hardware doesn't support PAE40\n");

        /* Enable the MMU with ASID 0 */
        mmu_setup_asid(NULL, 0);

        /* cache the pgd pointer in MMU SCRATCH reg (ARCv2 only) */
        mmu_setup_pgd(NULL, swapper_pg_dir);

        if (pae40_exist_but_not_enab())
                write_aux_reg(ARC_REG_TLBPD1HI, 0);
}

/*
 * TLB Programmer's Model uses Linear Indexes: 0 to {255, 511} for 128 x {2,4}
 * The mapping is Column-first.
 *              ---------------------   -----------
 *              |way0|way1|way2|way3|   |way0|way1|
 *              ---------------------   -----------
 * [set0]       |  0 |  1 |  2 |  3 |   |  0 |  1 |
 * [set1]       |  4 |  5 |  6 |  7 |   |  2 |  3 |
 *              ~                   ~   ~         ~
 * [set127]     | 508| 509| 510| 511|   | 254| 255|
 *              ---------------------   -----------
 * For normal operations we don't(must not) care how above works since
 * MMU cmd getIndex(vaddr) abstracts that out.
 * However for walking WAYS of a SET, we need to know this
 */
#define SET_WAY_TO_IDX(mmu, set, way)  ((set) * mmu->ways + (way))

/* Handling of Duplicate PD (TLB entry) in MMU.
 * -Could be due to buggy customer tapeouts or obscure kernel bugs
 * -MMU complaints not at the time of duplicate PD installation, but at the
 *      time of lookup matching multiple ways.
 * -Ideally these should never happen - but if they do - workaround by deleting
 *      the duplicate one.
 * -Knob to be verbose abt it.(TODO: hook them up to debugfs)
 */
volatile int dup_pd_silent; /* Be silent abt it or complain (default) */

void do_tlb_overlap_fault(unsigned long cause, unsigned long address,
                          struct pt_regs *regs)
{
        struct cpuinfo_arc_mmu *mmu = &mmuinfo;
        unsigned long flags;
        int set, n_ways = mmu->ways;

        n_ways = min(n_ways, 4);
        BUG_ON(mmu->ways > 4);

        local_irq_save(flags);

        /* loop thru all sets of TLB */
        for (set = 0; set < mmu->sets; set++) {

                int is_valid, way;
                unsigned int pd0[4];

                /* read out all the ways of current set */
                for (way = 0, is_valid = 0; way < n_ways; way++) {
                        write_aux_reg(ARC_REG_TLBINDEX,
                                          SET_WAY_TO_IDX(mmu, set, way));
                        write_aux_reg(ARC_REG_TLBCOMMAND, TLBRead);
                        pd0[way] = read_aux_reg(ARC_REG_TLBPD0);
                        is_valid |= pd0[way] & _PAGE_PRESENT;
                        pd0[way] &= PAGE_MASK;
                }

                /* If all the WAYS in SET are empty, skip to next SET */
                if (!is_valid)
                        continue;

                /* Scan the set for duplicate ways: needs a nested loop */
                for (way = 0; way < n_ways - 1; way++) {

                        int n;

                        if (!pd0[way])
                                continue;

                        for (n = way + 1; n < n_ways; n++) {
                                if (pd0[way] != pd0[n])
                                        continue;

                                if (!dup_pd_silent)
                                        pr_info("Dup TLB PD0 %08x @ set %d ways %d,%d\n",
                                                pd0[way], set, way, n);

                                /*
                                 * clear entry @way and not @n.
                                 * This is critical to our optimised loop
                                 */
                                pd0[way] = 0;
                                write_aux_reg(ARC_REG_TLBINDEX,
                                                SET_WAY_TO_IDX(mmu, set, way));
                                __tlb_entry_erase();
                        }
                }
        }

        local_irq_restore(flags);
}