Re: [PATCH v3 0/6] Static calls

[Nadav Amit]

> On Jan 11, 2019, at 8:07 AM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
> 
> On Fri, Jan 11, 2019 at 03:48:59PM +0000, Nadav Amit wrote:
>>> I liked the idea, BUT, how would it work for callee-saved PV ops?  In
>>> that case there's only one clobbered register to work with (rax).
>> 
>> Thatâs would be more tricky. How about using a per-CPU trampoline code to
>> hold a direct call to the target and temporarily disable preemption (which
>> might be simpler by disabling IRQs):
>> 

Allow me to simplify/correct:

>> Static-call modifier:
>> 
>>        1. synchronize_sched() to ensure per-cpu trampoline is not used
No need for (1) (We are going to sync using IPI).

>> 	2. Patches the jmp in a per-cpu trampoline (see below)
>> 	3. Saves the call source RIP in [per-cpu scratchpad RIP] (below)
Both do not need to be per-cpu

>> 	4. Configures the int3 handler to use static-call int3 handler
>> 	5. Patches the call target (as it currently does).
Note that text_poke_bp() would do eventually:

	on_each_cpu(do_sync_core, NULL, 1);

So you should know no cores run the trampoline after (5).