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/*
* 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 <asm/xen/hypercall.h>
#include "multicalls.h"
#define MC_BATCH 8
#define MC_ARGS (MC_BATCH * 32 / sizeof(u64))
struct mc_buffer {
struct multicall_entry entries[MC_BATCH];
u64 args[MC_ARGS];
unsigned mcidx, argidx;
};
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 = &__get_cpu_var(mc_buffer);
int ret = 0;
unsigned long flags;
BUG_ON(preemptible());
/* Disable interrupts in case someone comes in and queues
something in the middle */
local_irq_save(flags);
if (b->mcidx) {
int i;
if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
BUG();
for (i = 0; i < b->mcidx; i++)
if (b->entries[i].result < 0)
ret++;
b->mcidx = 0;
b->argidx = 0;
} else
BUG_ON(b->argidx != 0);
local_irq_restore(flags);
BUG_ON(ret);
}
struct multicall_space __xen_mc_entry(size_t args)
{
struct mc_buffer *b = &__get_cpu_var(mc_buffer);
struct multicall_space ret;
unsigned argspace = (args + sizeof(u64) - 1) / sizeof(u64);
BUG_ON(preemptible());
BUG_ON(argspace > MC_ARGS);
if (b->mcidx == MC_BATCH ||
(b->argidx + argspace) > MC_ARGS)
xen_mc_flush();
ret.mc = &b->entries[b->mcidx];
b->mcidx++;
ret.args = &b->args[b->argidx];
b->argidx += argspace;
return ret;
}
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