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kmod/core: improve performance for cumulative patching 

When multiple patch modules patch the same function, there's no need to
patch all the intermediate functions.  Just hook them all into the
original function and use the ftrace handler to find the newest one.

Also use a mutex in the register/unregister functions to protect changes
to kpatch_num_registered, kpatch_func_hash and calls to the ftrace
functions by other register/unregister invocations.
This commit is contained in:
Josh Poimboeuf 2014-03-17 10:36:11 -05:00
parent 37a756af58
commit 29227a0fbd
1 changed files with 42 additions and 13 deletions
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55
kmod/core/core.c
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@ -141,19 +141,8 @@ static int kpatch_apply_patch(void *data)
goto out;
for (i = 0; i < num_funcs; i++) {
struct kpatch_func *f;
struct kpatch_func *func = &funcs[i];
/* do any needed incremental patching */
/* TODO: performance */
hash_for_each_possible(kpatch_func_hash, f, node,
func->old_addr) {
if (f->old_addr == func->old_addr) {
func->old_addr = f->new_addr;
ref_module(func->mod, f->mod);
}
}
/* update the global list and go live */
hash_add(kpatch_func_hash, &func->node, func->old_addr);
}
@ -187,6 +176,14 @@ void kpatch_ftrace_handler(unsigned long ip, unsigned long parent_ip,
{
struct kpatch_func *f;
/*
* This is where the magic happens. Update regs->ip to tell ftrace to
* return to the new function.
*
* If there are multiple patch modules that have registered to patch
* the same function, the last one to register wins, as it'll be first
* in the hash bucket.
*/
preempt_disable_notrace();
hash_for_each_possible(kpatch_func_hash, f, node, ip) {
if (f->old_addr == ip) {
@ -214,10 +211,26 @@ int kpatch_register(struct module *mod, struct kpatch_func *funcs,
down(&kpatch_mutex);
for (i = 0; i < num_funcs; i++) {
struct kpatch_func *func = &funcs[i];
struct kpatch_func *f, *func = &funcs[i];
bool found = false;
func->mod = mod;
/*
* If any other modules have also patched this function, it
* already has an ftrace handler.
*/
hash_for_each_possible(kpatch_func_hash, f, node,
func->old_addr) {
if (f->old_addr == func->old_addr) {
found = true;
break;
}
}
if (found)
continue;
/* Add an ftrace handler for this function. */
ret = ftrace_set_filter_ip(&kpatch_ftrace_ops, func->old_addr,
0, 0);
if (ret) {
@ -285,8 +298,24 @@ int kpatch_unregister(struct module *mod, struct kpatch_func *funcs,
}
for (i = 0; i < num_funcs; i++) {
struct kpatch_func *func = &funcs[i];
struct kpatch_func *f, *func = &funcs[i];
bool found = false;
/*
* If any other modules have also patched this function, don't
* remove its ftrace handler.
*/
hash_for_each_possible(kpatch_func_hash, f, node,
func->old_addr) {
if (f->old_addr == func->old_addr) {
found = true;
break;
}
}
if (found)
continue;
/* Remove the ftrace handler for this function. */
ret = ftrace_set_filter_ip(&kpatch_ftrace_ops, func->old_addr,
1, 0);
if (ret) {