linux-kernel - Re: [PATCH v1 0/3] mm: fixup pfnmap memory failure handling

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Message-Id: <20251211121119.0ebfd65ed69b5d5f6537710a@linux-foundation.org>
Date: Thu, 11 Dec 2025 12:11:19 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: <ankita@...dia.com>
Cc: <vsethi@...dia.com>, <jgg@...dia.com>, <mochs@...dia.com>,
 <jgg@...pe.ca>, <skolothumtho@...dia.com>, <alex@...zbot.org>,
 <linmiaohe@...wei.com>, <nao.horiguchi@...il.com>, <cjia@...dia.com>,
 <zhiw@...dia.com>, <kjaju@...dia.com>, <yishaih@...dia.com>,
 <kevin.tian@...el.com>, <kvm@...r.kernel.org>,
 <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCH v1 0/3] mm: fixup pfnmap memory failure handling

On Thu, 11 Dec 2025 07:06:00 +0000 <ankita@...dia.com> wrote:

> It was noticed during 6.19 merge window that the patch series [1] to
> introduce memory failure handling for the PFNMAP memory is broken.
> 
> The expected behaviour of the series is to allow a driver (such as
> nvgrace-gpu) to register its device memory with the mm. The mm would
> then handle the poison on that registered memory region.
> 
> However, the following issues were identified in the patch series.
> 1. Faulty use of PFN instead of mapping file page offset to derive
> the usermode process VA corresponding to the mapping to PFN.
> 2. nvgrace-gpu code called the registration at mmap, exposing it
> to corruption. This may happen, when multiple mmap were called on the
> same BAR. This issue was also noticed by Linus Torvalds who reverted
> the patch [2].
> 
> This patch series addresses those issues.
> 
> Patch 1/3 fixes the first issue by translating PFN to page offset
> and using that information to send the SIGBUS to the mapping process.
> Patch 2/3 add stubs for CONFIG_MEMORY_FAILURE disabled.
> Patch 3/3 is a resend of the reverted change to register the device
> memory at the time of open instead of mmap.
> 

Strictly speaking, [1/3] is suitable for merging in the 6.19-rcX cycle
because it fixes a 6.19-rcX thing.  But [2/3] and [3/3] don't fix
anything and hence should be considered 6.20-rc1 material.  Yes?

So unless I'm missing something, I'll grab [1/3] as a 6.19-rcX hotfix. 
Please prepare the other two patches as a standalone series for
addition to mm.git after 6.19-rc1 is released.

Thanks.