diff options
Diffstat (limited to 'arch/x86/xen/multicalls.c')
| -rw-r--r-- | arch/x86/xen/multicalls.c | 209 |
1 files changed, 209 insertions, 0 deletions
diff --git a/arch/x86/xen/multicalls.c b/arch/x86/xen/multicalls.c new file mode 100644 index 000000000..2bce7958c --- /dev/null +++ b/arch/x86/xen/multicalls.c @@ -0,0 +1,209 @@ +// 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); + + 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 MC_DEBUG + memcpy(b->debug, b->entries, + b->mcidx * sizeof(struct multicall_entry)); +#endif + + if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0) + BUG(); + for (i = 0; i < b->mcidx; i++) + if (b->entries[i].result < 0) + ret++; + +#if MC_DEBUG + if (ret) { + printk(KERN_ERR "%d multicall(s) failed: cpu %d\n", + ret, smp_processor_id()); + dump_stack(); + for (i = 0; i < b->mcidx; i++) { + printk(KERN_DEBUG " call %2d/%d: op=%lu arg=[%lx] result=%ld\t%pF\n", + i+1, b->mcidx, + b->debug[i].op, + b->debug[i].args[0], + b->entries[i].result, + b->caller[i]); + } + } +#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); + + WARN_ON(ret); +} + +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; +} |