On Mon, Jul 07, 2025 at 12:10:43PM +0200, Christophe Leroy wrote:
>
> Le 04/07/2025 à 15:49, Mike Rapoport a écrit :
> > From: "Mike Rapoport (Microsoft)" <r...@kernel.org>
> >
> > The execmem_update_copy() that used text poking was required when memory
> > allocated from ROX cache was always read-only. Since now its permissions
> > can be switched to read-write there is no need in a function that updates
> > memory with text poking.
>
> Erm. Looks like I missed the patch that introduced this change.
>
> On some variant of powerpc, namely book3s/32, this is not feasible.
The only user of EXECMEM_ROX_CACHE for now is x86-64, we can always revisit
when powerpc book3s/32 would want to opt in to cache usage.
And it seems that [MODULES_VADDR, MODULES_END] is already mapped with
"large pages", isn't it?
> The granularity for setting the NX (non exec) bit is 256 Mbytes sections.
> So the area dedicated to execmem [MODULES_VADDR; MODULES_END[ always have
> the NX bit unset.
>
> You can change any page within this area from ROX to RWX but you can't make
> it RW without X. If you want RW without X you must map it in the VMALLOC
> area, as VMALLOC area have NX bit always set.
So what will happen when one callse
set_memory_nx()
set_memory_rw()
in such areas?
> Christophe
--
Sincerely yours,
Mike.
