Re: [RFC][PATCH] x86/mm: Sync all vmalloc mappings before text_poke()

[Steven Rostedt]

On Wed, 29 Apr 2020 12:59:41 +0200
Joerg Roedel <jroedel@xxxxxxx> wrote:

> >   use_temporary_mm() {
> >     switch_mm_irqs_off() {
> >       load_new_mm_cr3() {
> >         write_cr3() <<--- Lock up!  
> 
> I don't see how it could lock up in write_cr3(), at least on bare-metal.
> What is the environment this happens, 32 or 64 bit, in a VM or
> bare-metal?

64 bit bare-metal. In fact, it wasn't reproducible on a VM (according
to Tzvetomir, who was just using a Fedora kernel). I only tried it on
bare-metal.

> 
> I think it is more likely that your lockup is actually a page-fault
> loop, where the #PF handler does not map the faulting address correctly.

Sounds reasonable.

> 
> But I have to look closer into how text_poke() works before I can say
> more.
> 
> Btw, in case it happens on x86-64, does it also happen without
> vmalloc-stacks?

Just tried it out with !CONFIG_VMAP_STACKS and it still locks up :-/

-- Steve