Re: [PATCH v12 10/11] powerpc: mm: Use set_pte_at_unchecked() for early-boot / internal usages

[Pasha Tatashin <pasha.tatashin@soleen.com>]

On Tue, Apr 2, 2024 at 1:13 AM Rohan McLure <rmclure@linux.ibm.com> wrote:
>
> In the new set_ptes() API, set_pte_at() (a special case of set_ptes())
> is intended to be instrumented by the page table check facility. There
> are however several other routines that constitute the API for setting
> page table entries, including set_pmd_at() among others. Such routines
> are themselves implemented in terms of set_ptes_at().
>
> A future patch providing support for page table checking on powerpc
> must take care to avoid duplicate calls to
> page_table_check_p{te,md,ud}_set(). Allow for assignment of pte entries
> without instrumentation through the set_pte_at_unchecked() routine
> introduced in this patch.
>
> Cause API-facing routines that call set_pte_at() to instead call
> set_pte_at_unchecked(), which will remain uninstrumented by page
> table check. set_ptes() is itself implemented by calls to
> __set_pte_at(), so this eliminates redundant code.
>
> Also prefer set_pte_at_unchecked() in early-boot usages which should not be
> instrumented.

Would not the early-boot usage be all kernel mappings that are ignored
by page table check anways? Sounds like it is better to only use the
set_pte_at_unchecked() version where it is really needed, which is to
avoid double counting. This will keep the usage of this function only
for one purpose that is easy to follow.

Pasha