Received-SPF: pass (google.com: domain of linux-kernel+bounces-204335-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.199.223 as permitted sender) client-ip=147.75.199.223;
Date: Thu, 6 Jun 2024 09:14:01 -0400
From: Peter Xu <peterx@redhat.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Dan Williams <dan.j.williams@intel.com>,
	Pasha Tatashin <pasha.tatashin@soleen.com>
Subject: Re: [PATCH] mm/page_table_check: Fix crash on ZONE_DEVICE
Message-ID: <ZmG2GciaQRTk-Yam@x1n>
References: <20240605212146.994486-1-peterx@redhat.com>
 <20240605150543.87c81189fa7cb562e73fa0b8@linux-foundation.org>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <20240605150543.87c81189fa7cb562e73fa0b8@linux-foundation.org>

On Wed, Jun 05, 2024 at 03:05:43PM -0700, Andrew Morton wrote:
> On Wed,  5 Jun 2024 17:21:46 -0400 Peter Xu <peterx@redhat.com> wrote:
> 
> > Not all pages may apply to pgtable check.  One example is ZONE_DEVICE
> > pages: they map PFNs directly, and they don't allocate page_ext at all even
> > if there's struct page around.  One may reference devm_memremap_pages().
> > 
> > When both ZONE_DEVICE and page-table-check enabled, then try to map some
> > dax memories, one can trigger kernel bug constantly now when the kernel was
> > trying to inject some pfn maps on the dax device:
> > 
> >  kernel BUG at mm/page_table_check.c:55!
> > 
> > While it's pretty legal to use set_pxx_at() for ZONE_DEVICE pages for page
> > fault resolutions, skip all the checks if page_ext doesn't even exist in
> > pgtable checker, which applies to ZONE_DEVICE but maybe more.
> 
> Do we have a Reported-by: for this one?

Nop, I just hit that when I started to look at the dax issues.

> 
> And a Fixes?  It looks like df4e817b7108?

Yes that commit should be proper.

Thanks,

-- 
Peter Xu