linux-kernel - Re: [PATCH v2 1/1] mm: Allow detection of wrong arch_enter_lazy_mmu

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Message-ID: <Z/fiwRdmczI8f3nt@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com>
Date: Thu, 10 Apr 2025 17:24:49 +0200
From: Alexander Gordeev <agordeev@...ux.ibm.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH v2 1/1] mm: Allow detection of wrong
 arch_enter_lazy_mmu_mode() context

On Tue, Apr 08, 2025 at 06:48:31PM +0200, Alexander Gordeev wrote:
> The lazy MMU batching may be only be entered and left under the
> protection of the page table locks for all page tables which may
> be modified. Yet, there were cases arch_enter_lazy_mmu_mode()
> was called without the locks taken, e.g. commit b9ef323ea168
> ("powerpc/64s: Disable preemption in hash lazy mmu mode").
> 
> Make default arch_enter|leave|flush_lazy_mmu_mode() callbacks
> complain at least in case the preemption is enabled to detect
> wrong contexts.
> 
> Most platforms do not implement the callbacks, so to aovid a
> performance impact allow the complaint when CONFIG_DEBUG_VM
> option is enabled only.
> 
> Signed-off-by: Alexander Gordeev <agordeev@...ux.ibm.com>
> ---
>  include/linux/pgtable.h | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)

Andrew,

Following [1] comment to "[PATCH v2 3/3] mm: Protect kernel pgtables in
apply_to_pte_range()" I think this patch should also be dropped.

1. https://lore.kernel.org/all/Z%2FfauW5hDSt+ciwr@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com/

Thanks!