On 18/12/2025 09:36, Yeoreum Yun wrote:

Hi,

quoted

On Fri 12-12-25 16:18:32, Yeoreum Yun wrote:

quoted

linear_map_split_to_ptes() and __kpti_install_ng_mappings()
are called as callback of stop_machine().
That means these functions context are preemption disabled.

Unfortunately, under PREEMPT_RT, the pagetable_alloc() or
__get_free_pages() couldn't be called in this context
since spin lock that becomes sleepable on RT,
potentially causing a sleep during page allocation.

To address this, pagetable_alloc_nolock().

As you cannot tolerate allocation failure and this is pretty much
permanent allocation (AFAIU) why don't you use a static allocation?

Because of when bbl2_noabort is supported, that pages doesn't need to.
If static alloc, that would be a waste in the system where bbl2_noabort
is supported.

When I tested, these extra pages are more than 40 in my FVP.
So, it would be better dynamic allocation and I think since it's quite a
early time, it's probably not failed that's why former code runs as it
is.

The required allocation size is also a function of the size of the installed RAM
so a static worst case allocation would consume all the RAM on small systems.

--
Sincerely,
Yeoreum Yun