icswx.c

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/*
 *  ICSWX and ACOP Management
 *
 *  Copyright (C) 2011 Anton Blanchard, IBM Corp. <[email protected]>
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 *
 */

#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/spinlock.h>
#include <linux/module.h>
#include <linux/uaccess.h>

#include "icswx.h"

/*
 * The processor and its L2 cache cause the icswx instruction to
 * generate a COP_REQ transaction on PowerBus. The transaction has no
 * address, and the processor does not perform an MMU access to
 * authenticate the transaction. The command portion of the PowerBus
 * COP_REQ transaction includes the LPAR_ID (LPID) and the coprocessor
 * Process ID (PID), which the coprocessor compares to the authorized
 * LPID and PID held in the coprocessor, to determine if the process
 * is authorized to generate the transaction.  The data of the COP_REQ
 * transaction is 128-byte or less in size and is placed in cacheable
 * memory on a 128-byte cache line boundary.
 *
 * The task to use a coprocessor should use use_cop() to mark the use
 * of the Coprocessor Type (CT) and context switching. On a server
 * class processor, the PID register is used only for coprocessor
 * management + * and so a coprocessor PID is allocated before
 * executing icswx + * instruction. Drop_cop() is used to free the
 * coprocessor PID.
 *
 * Example:
 * Host Fabric Interface (HFI) is a PowerPC network coprocessor.
 * Each HFI have multiple windows. Each HFI window serves as a
 * network device sending to and receiving from HFI network.
 * HFI immediate send function uses icswx instruction. The immediate
 * send function allows small (single cache-line) packets be sent
 * without using the regular HFI send FIFO and doorbell, which are
 * much slower than immediate send.
 *
 * For each task intending to use HFI immediate send, the HFI driver
 * calls use_cop() to obtain a coprocessor PID for the task.
 * The HFI driver then allocate a free HFI window and save the
 * coprocessor PID to the HFI window to allow the task to use the
 * HFI window.
 *
 * The HFI driver repeatedly creates immediate send packets and
 * issues icswx instruction to send data through the HFI window.
 * The HFI compares the coprocessor PID in the CPU PID register
 * to the PID held in the HFI window to determine if the transaction
 * is allowed.
 *
 * When the task to release the HFI window, the HFI driver calls
 * drop_cop() to release the coprocessor PID.
 */

void switch_cop(struct mm_struct *next)
{
#ifdef CONFIG_ICSWX_PID
    mtspr(SPRN_PID, next->context.cop_pid);
#endif
    mtspr(SPRN_ACOP, next->context.acop);
}

int use_cop(unsigned long acop, struct mm_struct *mm)
{
    int ret;

    if (!cpu_has_feature(CPU_FTR_ICSWX))
        return -ENODEV;

    if (!mm || !acop)
        return -EINVAL;

    /* The page_table_lock ensures mm_users won't change under us */
    spin_lock(&mm->page_table_lock);
    spin_lock(mm->context.cop_lockp);

    ret = get_cop_pid(mm);
    if (ret < 0)
        goto out;

    /* update acop */
    mm->context.acop |= acop;

    sync_cop(mm);

    /*
     * If this is a threaded process then there might be other threads
     * running. We need to send an IPI to force them to pick up any
     * change in PID and ACOP.
     */
    if (atomic_read(&mm->mm_users) > 1)
        smp_call_function(sync_cop, mm, 1);

out:
    spin_unlock(mm->context.cop_lockp);
    spin_unlock(&mm->page_table_lock);

    return ret;
}
EXPORT_SYMBOL_GPL(use_cop);

void drop_cop(unsigned long acop, struct mm_struct *mm)
{
    int free_pid;

    if (!cpu_has_feature(CPU_FTR_ICSWX))
        return;

    if (WARN_ON_ONCE(!mm))
        return;

    /* The page_table_lock ensures mm_users won't change under us */
    spin_lock(&mm->page_table_lock);
    spin_lock(mm->context.cop_lockp);

    mm->context.acop &= ~acop;

    free_pid = disable_cop_pid(mm);
    sync_cop(mm);

    /*
     * If this is a threaded process then there might be other threads
     * running. We need to send an IPI to force them to pick up any
     * change in PID and ACOP.
     */
    if (atomic_read(&mm->mm_users) > 1)
        smp_call_function(sync_cop, mm, 1);

    if (free_pid != COP_PID_NONE)
        free_cop_pid(free_pid);

    spin_unlock(mm->context.cop_lockp);
    spin_unlock(&mm->page_table_lock);
}
EXPORT_SYMBOL_GPL(drop_cop);

static int acop_use_cop(int ct)
{
    /* There is no alternate policy, yet */
    return -1;
}

/*
 * Get the instruction word at the NIP
 */
static u32 acop_get_inst(struct pt_regs *regs)
{
    u32 inst;
    u32 __user *p;

    p = (u32 __user *)regs->nip;
    if (!access_ok(VERIFY_READ, p, sizeof(*p)))
        return 0;

    if (__get_user(inst, p))
        return 0;

    return inst;
}

int acop_handle_fault(struct pt_regs *regs, unsigned long address,
              unsigned long error_code)
{
    int ct;
    u32 inst = 0;

    if (!cpu_has_feature(CPU_FTR_ICSWX)) {
        pr_info("No coprocessors available");
        _exception(SIGILL, regs, ILL_ILLOPN, address);
    }

    if (!user_mode(regs)) {
        /* this could happen if the HV denies the
         * kernel access, for now we just die */
        die("ICSWX from kernel failed", regs, SIGSEGV);
    }

    /* Some implementations leave us a hint for the CT */
    ct = ICSWX_GET_CT_HINT(error_code);
    if (ct < 0) {
        /* we have to peek at the instruction word to figure out CT */
        u32 ccw;
        u32 rs;

        inst = acop_get_inst(regs);
        if (inst == 0)
            return -1;

        rs = (inst >> (31 - 10)) & 0x1f;
        ccw = regs->gpr[rs];
        ct = (ccw >> 16) & 0x3f;
    }

    /*
     * We could be here because another thread has enabled acop
     * but the ACOP register has yet to be updated.
     *
     * This should have been taken care of by the IPI to sync all
     * the threads (see smp_call_function(sync_cop, mm, 1)), but
     * that could take forever if there are a significant amount
     * of threads.
     *
     * Given the number of threads on some of these systems,
     * perhaps this is the best way to sync ACOP rather than whack
     * every thread with an IPI.
     */
    if ((acop_copro_type_bit(ct) & current->active_mm->context.acop) != 0) {
        sync_cop(current->active_mm);
        return 0;
    }

    /* check for alternate policy */
    if (!acop_use_cop(ct))
        return 0;

    /* at this point the CT is unknown to the system */
    pr_warn("%s[%d]: Coprocessor %d is unavailable\n",
        current->comm, current->pid, ct);

    /* get inst if we don't already have it */
    if (inst == 0) {
        inst = acop_get_inst(regs);
        if (inst == 0)
            return -1;
    }

    /* Check if the instruction is the "record form" */
    if (inst & 1) {
        /*
         * the instruction is "record" form so we can reject
         * using CR0
         */
        regs->ccr &= ~(0xful << 28);
        regs->ccr |= ICSWX_RC_NOT_FOUND << 28;

        /* Move on to the next instruction */
        regs->nip += 4;
    } else {
        /*
         * There is no architected mechanism to report a bad
         * CT so we could either SIGILL or report nothing.
         * Since the non-record version should only bu used
         * for "hints" or "don't care" we should probably do
         * nothing.  However, I could see how some people
         * might want an SIGILL so it here if you want it.
         */
#ifdef CONFIG_PPC_ICSWX_USE_SIGILL
        _exception(SIGILL, regs, ILL_ILLOPN, address);
#else
        regs->nip += 4;
#endif
    }

    return 0;
}
EXPORT_SYMBOL_GPL(acop_handle_fault);