// SPDX-License-Identifier: GPL-2.0
/*
 * Xen hypercall batching.
 *
 * Xen allows multiple hypercalls to be issued at once, using the
 * multicall interface.  This allows the cost of trapping into the
 * hypervisor to be amortized over several calls.
 *
 * This file implements a simple interface for multicalls.  There's a
 * per-cpu buffer of outstanding multicalls.  When you want to queue a
 * multicall for issuing, you can allocate a multicall slot for the
 * call and its arguments, along with storage for space which is
 * pointed to by the arguments (for passing pointers to structures,
 * etc).  When the multicall is actually issued, all the space for the
 * commands and allocated memory is freed for reuse.
 *
 * Multicalls are flushed whenever any of the buffers get full, or
 * when explicitly requested.  There's no way to get per-multicall
 * return results back.  It will BUG if any of the multicalls fail.
 *
 * Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
 */
#include <linux/percpu.h>
#include <linux/hardirq.h>
#include <linux/debugfs.h>

#include <asm/xen/hypercall.h>

#include "multicalls.h"
#include "debugfs.h"

#define MC_BATCH        32

#define MC_DEBUG        0

#define MC_ARGS         (MC_BATCH * 16)


struct mc_buffer {
        unsigned mcidx, argidx, cbidx;
        struct multicall_entry entries[MC_BATCH];
#if MC_DEBUG
        struct multicall_entry debug[MC_BATCH];
        void *caller[MC_BATCH];
#endif
        unsigned char args[MC_ARGS];
        struct callback {
                void (*fn)(void *);
                void *data;
        } callbacks[MC_BATCH];
};

static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);

void xen_mc_flush(void)
{
        struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
        struct multicall_entry *mc;
        int ret = 0;
        unsigned long flags;
        int i;

        BUG_ON(preemptible());

        /* Disable interrupts in case someone comes in and queues
           something in the middle */
        local_irq_save(flags);

        trace_xen_mc_flush(b->mcidx, b->argidx, b->cbidx);

#if MC_DEBUG
        memcpy(b->debug, b->entries,
               b->mcidx * sizeof(struct multicall_entry));
#endif

        switch (b->mcidx) {
        case 0:
                /* no-op */
                BUG_ON(b->argidx != 0);
                break;

        case 1:
                /* Singleton multicall - bypass multicall machinery
                   and just do the call directly. */
                mc = &b->entries[0];

                mc->result = xen_single_call(mc->op, mc->args[0], mc->args[1],
                                             mc->args[2], mc->args[3],
                                             mc->args[4]);
                ret = mc->result < 0;
                break;

        default:
                if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
                        BUG();
                for (i = 0; i < b->mcidx; i++)
                        if (b->entries[i].result < 0)
                                ret++;
        }

        if (WARN_ON(ret)) {
                pr_err("%d of %d multicall(s) failed: cpu %d\n",
                       ret, b->mcidx, smp_processor_id());
                for (i = 0; i < b->mcidx; i++) {
                        if (b->entries[i].result < 0) {
#if MC_DEBUG
                                pr_err("  call %2d: op=%lu arg=[%lx] result=%ld\t%pS\n",
                                       i + 1,
                                       b->debug[i].op,
                                       b->debug[i].args[0],
                                       b->entries[i].result,
                                       b->caller[i]);
#else
                                pr_err("  call %2d: op=%lu arg=[%lx] result=%ld\n",
                                       i + 1,
                                       b->entries[i].op,
                                       b->entries[i].args[0],
                                       b->entries[i].result);
#endif
                        }
                }
        }

        b->mcidx = 0;
        b->argidx = 0;

        for (i = 0; i < b->cbidx; i++) {
                struct callback *cb = &b->callbacks[i];

                (*cb->fn)(cb->data);
        }
        b->cbidx = 0;

        local_irq_restore(flags);
}

struct multicall_space __xen_mc_entry(size_t args)
{
        struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
        struct multicall_space ret;
        unsigned argidx = roundup(b->argidx, sizeof(u64));

        trace_xen_mc_entry_alloc(args);

        BUG_ON(preemptible());
        BUG_ON(b->argidx >= MC_ARGS);

        if (unlikely(b->mcidx == MC_BATCH ||
                     (argidx + args) >= MC_ARGS)) {
                trace_xen_mc_flush_reason((b->mcidx == MC_BATCH) ?
                                          XEN_MC_FL_BATCH : XEN_MC_FL_ARGS);
                xen_mc_flush();
                argidx = roundup(b->argidx, sizeof(u64));
        }

        ret.mc = &b->entries[b->mcidx];
#if MC_DEBUG
        b->caller[b->mcidx] = __builtin_return_address(0);
#endif
        b->mcidx++;
        ret.args = &b->args[argidx];
        b->argidx = argidx + args;

        BUG_ON(b->argidx >= MC_ARGS);
        return ret;
}

struct multicall_space xen_mc_extend_args(unsigned long op, size_t size)
{
        struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
        struct multicall_space ret = { NULL, NULL };

        BUG_ON(preemptible());
        BUG_ON(b->argidx >= MC_ARGS);

        if (unlikely(b->mcidx == 0 ||
                     b->entries[b->mcidx - 1].op != op)) {
                trace_xen_mc_extend_args(op, size, XEN_MC_XE_BAD_OP);
                goto out;
        }

        if (unlikely((b->argidx + size) >= MC_ARGS)) {
                trace_xen_mc_extend_args(op, size, XEN_MC_XE_NO_SPACE);
                goto out;
        }

        ret.mc = &b->entries[b->mcidx - 1];
        ret.args = &b->args[b->argidx];
        b->argidx += size;

        BUG_ON(b->argidx >= MC_ARGS);

        trace_xen_mc_extend_args(op, size, XEN_MC_XE_OK);
out:
        return ret;
}

void xen_mc_callback(void (*fn)(void *), void *data)
{
        struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
        struct callback *cb;

        if (b->cbidx == MC_BATCH) {
                trace_xen_mc_flush_reason(XEN_MC_FL_CALLBACK);
                xen_mc_flush();
        }

        trace_xen_mc_callback(fn, data);

        cb = &b->callbacks[b->cbidx++];
        cb->fn = fn;
        cb->data = data;
}