linux-kernel - Re: [PATCH v2 3/3] mm: Protect kernel pgtables in apply_to_pte

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Message-Id: <20250410154744.44991b2abe5f842e34320917@linux-foundation.org>
Date: Thu, 10 Apr 2025 15:47:44 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>, Hugh Dickins
 <hughd@...gle.com>, Nicholas Piggin <npiggin@...il.com>, Guenter Roeck
 <linux@...ck-us.net>, Juergen Gross <jgross@...e.com>, Jeremy Fitzhardinge
 <jeremy@...p.org>, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 kasan-dev@...glegroups.com, sparclinux@...r.kernel.org,
 xen-devel@...ts.xenproject.org, linuxppc-dev@...ts.ozlabs.org,
 linux-s390@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 3/3] mm: Protect kernel pgtables in
 apply_to_pte_range()

On Thu, 10 Apr 2025 16:50:33 +0200 Alexander Gordeev <agordeev@...ux.ibm.com> wrote:

> On Tue, Apr 08, 2025 at 06:07:32PM +0200, Alexander Gordeev wrote:
> 
> Hi Andrew,
> 
> > The lazy MMU mode can only be entered and left under the protection
> > of the page table locks for all page tables which may be modified.
> 
> Heiko Carstens noticed that the above claim is not valid, since
> v6.15-rc1 commit 691ee97e1a9d ("mm: fix lazy mmu docs and usage"),
> which restates it to:
> 
> "In the general case, no lock is guaranteed to be held between entry and exit
> of the lazy mode. So the implementation must assume preemption may be enabled"
> 
> That effectively invalidates this patch, so it needs to be dropped.
> 
> Patch 2 still could be fine, except -stable and Fixes tags and it does
> not need to aim 6.15-rcX. Do you want me to repost it?

I dropped the whole series - let's start again.