// SPDX-License-Identifier: GPL-2.0
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/*
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* Xen hypercall batching.
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*
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* Xen allows multiple hypercalls to be issued at once, using the
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* multicall interface. This allows the cost of trapping into the
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* hypervisor to be amortized over several calls.
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*
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* This file implements a simple interface for multicalls. There's a
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* per-cpu buffer of outstanding multicalls. When you want to queue a
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* multicall for issuing, you can allocate a multicall slot for the
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* call and its arguments, along with storage for space which is
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* pointed to by the arguments (for passing pointers to structures,
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* etc). When the multicall is actually issued, all the space for the
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* commands and allocated memory is freed for reuse.
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*
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* Multicalls are flushed whenever any of the buffers get full, or
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* when explicitly requested. There's no way to get per-multicall
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* return results back. It will BUG if any of the multicalls fail.
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*
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* Jeremy Fitzhardinge <jeremy@xensource.com>, XenSource Inc, 2007
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*/
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#include <linux/percpu.h>
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#include <linux/hardirq.h>
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#include <linux/debugfs.h>
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#include <asm/xen/hypercall.h>
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#include "multicalls.h"
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#include "debugfs.h"
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#define MC_BATCH 32
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#define MC_DEBUG 0
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#define MC_ARGS (MC_BATCH * 16)
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struct mc_buffer {
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unsigned mcidx, argidx, cbidx;
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struct multicall_entry entries[MC_BATCH];
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#if MC_DEBUG
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struct multicall_entry debug[MC_BATCH];
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void *caller[MC_BATCH];
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#endif
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unsigned char args[MC_ARGS];
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struct callback {
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void (*fn)(void *);
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void *data;
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} callbacks[MC_BATCH];
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};
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static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
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DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
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void xen_mc_flush(void)
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{
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struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
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struct multicall_entry *mc;
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int ret = 0;
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unsigned long flags;
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int i;
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BUG_ON(preemptible());
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/* Disable interrupts in case someone comes in and queues
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something in the middle */
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local_irq_save(flags);
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trace_xen_mc_flush(b->mcidx, b->argidx, b->cbidx);
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switch (b->mcidx) {
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case 0:
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/* no-op */
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BUG_ON(b->argidx != 0);
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break;
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case 1:
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/* Singleton multicall - bypass multicall machinery
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and just do the call directly. */
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mc = &b->entries[0];
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mc->result = xen_single_call(mc->op, mc->args[0], mc->args[1],
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mc->args[2], mc->args[3],
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mc->args[4]);
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ret = mc->result < 0;
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break;
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default:
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#if MC_DEBUG
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memcpy(b->debug, b->entries,
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b->mcidx * sizeof(struct multicall_entry));
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#endif
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if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
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BUG();
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for (i = 0; i < b->mcidx; i++)
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if (b->entries[i].result < 0)
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ret++;
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#if MC_DEBUG
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if (ret) {
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printk(KERN_ERR "%d multicall(s) failed: cpu %d\n",
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ret, smp_processor_id());
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dump_stack();
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for (i = 0; i < b->mcidx; i++) {
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printk(KERN_DEBUG " call %2d/%d: op=%lu arg=[%lx] result=%ld\t%pF\n",
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i+1, b->mcidx,
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b->debug[i].op,
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b->debug[i].args[0],
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b->entries[i].result,
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b->caller[i]);
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}
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}
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#endif
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}
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b->mcidx = 0;
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b->argidx = 0;
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for (i = 0; i < b->cbidx; i++) {
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struct callback *cb = &b->callbacks[i];
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(*cb->fn)(cb->data);
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}
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b->cbidx = 0;
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local_irq_restore(flags);
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WARN_ON(ret);
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}
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struct multicall_space __xen_mc_entry(size_t args)
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{
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struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
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struct multicall_space ret;
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unsigned argidx = roundup(b->argidx, sizeof(u64));
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trace_xen_mc_entry_alloc(args);
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BUG_ON(preemptible());
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BUG_ON(b->argidx >= MC_ARGS);
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if (unlikely(b->mcidx == MC_BATCH ||
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(argidx + args) >= MC_ARGS)) {
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trace_xen_mc_flush_reason((b->mcidx == MC_BATCH) ?
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XEN_MC_FL_BATCH : XEN_MC_FL_ARGS);
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xen_mc_flush();
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argidx = roundup(b->argidx, sizeof(u64));
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}
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ret.mc = &b->entries[b->mcidx];
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#if MC_DEBUG
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b->caller[b->mcidx] = __builtin_return_address(0);
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#endif
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b->mcidx++;
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ret.args = &b->args[argidx];
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b->argidx = argidx + args;
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BUG_ON(b->argidx >= MC_ARGS);
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return ret;
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}
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struct multicall_space xen_mc_extend_args(unsigned long op, size_t size)
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{
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struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
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struct multicall_space ret = { NULL, NULL };
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BUG_ON(preemptible());
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BUG_ON(b->argidx >= MC_ARGS);
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if (unlikely(b->mcidx == 0 ||
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b->entries[b->mcidx - 1].op != op)) {
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trace_xen_mc_extend_args(op, size, XEN_MC_XE_BAD_OP);
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goto out;
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}
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if (unlikely((b->argidx + size) >= MC_ARGS)) {
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trace_xen_mc_extend_args(op, size, XEN_MC_XE_NO_SPACE);
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goto out;
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}
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ret.mc = &b->entries[b->mcidx - 1];
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ret.args = &b->args[b->argidx];
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b->argidx += size;
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BUG_ON(b->argidx >= MC_ARGS);
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trace_xen_mc_extend_args(op, size, XEN_MC_XE_OK);
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out:
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return ret;
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}
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void xen_mc_callback(void (*fn)(void *), void *data)
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{
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struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
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struct callback *cb;
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if (b->cbidx == MC_BATCH) {
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trace_xen_mc_flush_reason(XEN_MC_FL_CALLBACK);
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xen_mc_flush();
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}
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trace_xen_mc_callback(fn, data);
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cb = &b->callbacks[b->cbidx++];
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cb->fn = fn;
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cb->data = data;
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}
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