Re: [PATCH v3 2/7] x86/jump_label: Use text_poke_early() during early_init

[Thomas Gleixner <tglx@linutronix.de>]

On Mon, 5 Nov 2018, Andy Lutomirski wrote:
> On Mon, Nov 5, 2018 at 11:25 AM Nadav Amit <namit@vmware.com> wrote:
> Linus, hpa, or Dave, a question for you: suppose I map some page
> writably, write to it, then upgrade permissions to allow execute.
> Must I force all CPUs that might execute from it without first
> serializing to serialize?  I suspect this doesn't really affect user
> code, but it may affect the module loader.
> 
> To be safe, shouldn't the module loader broadcast an IPI to
> sync_core() everywhere after loading a module and before making it
> runnable, regardless of alternative patching?
> 
> IOW, the right sequence of events probably ought to me:
> 
> 1. Allocate the memory and map it.
> 2. Copy in the text.
> 3. Patch alternatives, etc.  This is logically just like (2) from an
> architectural perspective -- we're just writing to memory that won't
> be executed.
> 4. Serialize everything.
> 5. Run it!

I'd make that:

1. Allocate the memory and map it RW
2. Copy in the text.
3. Patch alternatives, etc.  This is logically just like (2) from an
   architectural perspective -- we're just writing to memory that won't
   be executed.
4. Map it RX
5. Serialize everything.
6. Run it!

Thanks,

	tglx