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// 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 <linux/jump_label.h>
#include <linux/printk.h>
#include <asm/xen/hypercall.h>
#include "xen-ops.h"
#define MC_BATCH 32
#define MC_ARGS (MC_BATCH * 16)
struct mc_buffer {
unsigned mcidx, argidx, cbidx;
struct multicall_entry entries[MC_BATCH];
unsigned char args[MC_ARGS];
struct callback {
void (*fn)(void *);
void *data;
} callbacks[MC_BATCH];
};
struct mc_debug_data {
struct multicall_entry entries[MC_BATCH];
void *caller[MC_BATCH];
size_t argsz[MC_BATCH];
unsigned long *args[MC_BATCH];
};
static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
static struct mc_debug_data mc_debug_data_early __initdata;
static DEFINE_PER_CPU(struct mc_debug_data *, mc_debug_data) =
&mc_debug_data_early;
static struct mc_debug_data __percpu *mc_debug_data_ptr;
DEFINE_PER_CPU(unsigned long, xen_mc_irq_flags);
static struct static_key mc_debug __ro_after_init;
static bool mc_debug_enabled __initdata;
static int __init xen_parse_mc_debug(char *arg)
{
mc_debug_enabled = true;
static_key_slow_inc(&mc_debug);
return 0;
}
early_param("xen_mc_debug", xen_parse_mc_debug);
void mc_percpu_init(unsigned int cpu)
{
per_cpu(mc_debug_data, cpu) = per_cpu_ptr(mc_debug_data_ptr, cpu);
}
static int __init mc_debug_enable(void)
{
unsigned long flags;
if (!mc_debug_enabled)
return 0;
mc_debug_data_ptr = alloc_percpu(struct mc_debug_data);
if (!mc_debug_data_ptr) {
pr_err("xen_mc_debug inactive\n");
static_key_slow_dec(&mc_debug);
return -ENOMEM;
}
/* Be careful when switching to percpu debug data. */
local_irq_save(flags);
xen_mc_flush();
mc_percpu_init(0);
local_irq_restore(flags);
pr_info("xen_mc_debug active\n");
return 0;
}
early_initcall(mc_debug_enable);
/* Number of parameters of hypercalls used via multicalls. */
static const uint8_t hpcpars[] = {
[__HYPERVISOR_mmu_update] = 4,
[__HYPERVISOR_stack_switch] = 2,
[__HYPERVISOR_fpu_taskswitch] = 1,
[__HYPERVISOR_update_descriptor] = 2,
[__HYPERVISOR_update_va_mapping] = 3,
[__HYPERVISOR_mmuext_op] = 4,
};
static void print_debug_data(struct mc_buffer *b, struct mc_debug_data *mcdb,
int idx)
{
unsigned int arg;
unsigned int opidx = mcdb->entries[idx].op & 0xff;
unsigned int pars = 0;
pr_err(" call %2d: op=%lu result=%ld caller=%pS ", idx + 1,
mcdb->entries[idx].op, b->entries[idx].result,
mcdb->caller[idx]);
if (opidx < ARRAY_SIZE(hpcpars))
pars = hpcpars[opidx];
if (pars) {
pr_cont("pars=");
for (arg = 0; arg < pars; arg++)
pr_cont("%lx ", mcdb->entries[idx].args[arg]);
}
if (mcdb->argsz[idx]) {
pr_cont("args=");
for (arg = 0; arg < mcdb->argsz[idx] / 8; arg++)
pr_cont("%lx ", mcdb->args[idx][arg]);
}
pr_cont("\n");
}
void xen_mc_flush(void)
{
struct mc_buffer *b = this_cpu_ptr(&mc_buffer);
struct multicall_entry *mc;
struct mc_debug_data *mcdb = NULL;
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 (static_key_false(&mc_debug)) {
mcdb = __this_cpu_read(mc_debug_data);
memcpy(mcdb->entries, b->entries,
b->mcidx * sizeof(struct multicall_entry));
}
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 (static_key_false(&mc_debug)) {
print_debug_data(b, mcdb, i);
} else if (b->entries[i].result < 0) {
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);
}
}
}
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 (static_key_false(&mc_debug)) {
struct mc_debug_data *mcdb = __this_cpu_read(mc_debug_data);
mcdb->caller[b->mcidx] = __builtin_return_address(0);
mcdb->argsz[b->mcidx] = args;
mcdb->args[b->mcidx] = (unsigned long *)(&b->args[argidx]);
}
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;
}