Message-ID: <CACw3F51k=sFtXB1JE3HCcXP6EA0Tt4Yf44VUi3JLz0bgW-aArQ@mail.gmail.com>
Date: Fri, 16 Jan 2026 17:46:27 -0800
From: Jiaqi Yan <jiaqiyan@...gle.com>
To: ankita@...dia.com
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	Axel Rasmussen <axelrasmussen@...gle.com>
Subject: Re: [PATCH v5 0/3] mm: Implement ECC handling for pfn with no struct page

On Sun, Nov 2, 2025 at 10:45 AM <ankita@...dia.com> wrote:
>
> From: Ankit Agrawal <ankita@...dia.com>
>
> Poison (or ECC) errors can be very common on a large size cluster.
> The kernel MM currently handles ECC errors / poison only on memory page
> backed by struct page. The handling is currently missing for the PFNMAP
> memory that does not have struct pages. The series adds such support.
>
> Implement a new ECC handling for memory without struct pages. Kernel MM
> expose registration APIs to allow modules that are managing the device
> to register its device memory region. MM then tracks such regions using
> interval tree.
>
> The mechanism is largely similar to that of ECC on pfn with struct pages.
> If there is an ECC error on a pfn, all the mapping to it are identified
> and a SIGBUS is sent to the user space processes owning those mappings.
> Note that there is one primary difference versus the handling of the
> poison on struct pages, which is to skip unmapping to the faulty PFN.
> This is done to handle the huge PFNMAP support added recently [1] that
> enables VM_PFNMAP vmas to map at PMD or PUD level. A poison to a PFN
> mapped in such as way would need breaking the PMD/PUD mapping into PTEs
> that will get mirrored into the S2. This can greatly increase the cost
> of table walks and have a major performance impact.
>
> nvgrace-gpu-vfio-pci module maps the device memory to user VA (Qemu) using
> remap_pfn_range without being added to the kernel [2]. These device memory
> PFNs are not backed by struct page. So make nvgrace-gpu-vfio-pci module
> make use of the mechanism to get poison handling support on the device
> memory.
>
> Patch rebased to v6.17-rc7.
>
> Signed-off-by: Ankit Agrawal <ankita@...dia.com>
> ---
>
> Link: https://lore.kernel.org/all/20251026141919.2261-1-ankita@nvidia.com/ [v4]
>
> v4 -> v5
> - Removed pfn_space NULL checks. Instead a wrong parameter would cause
> a panic. (Thanks Andrew Morton for suggestion)
> - Log message to mention kmalloc allocation error and the failure to
> kill a process. (Thanks Andrew Morton)
> - Comments with 80 chars.
>
> v3 -> v4
> - Added guards in memory_failure_pfn, register, unregister function to
> simplify code. (Thanks Ira Weiny for suggestion).
> - Collected reviewed-by from Shuai Xue (Thanks!) on the mm GHES patch. Also
> moved it to the front of the series.
> - Added check for interval_tree_iter_first before removing the device
> memory region. (Thanks Jiaqi Yan for suggestion)
> - If pfn doesn't belong to any address space mapping, returning
> MF_IGNORED (Thanks Miaohe Lin for suggestion).
> - Updated patch commit to add more details on the perf impact on
> HUGE PFNMAP (Thanks Jason Gunthorpe, Tony Luck for suggestion).
>
> v2 -> v3
> - Rebased to v6.17-rc7.
> - Skipped the unmapping of PFNMAP during reception of poison. Suggested by
> Jason Gunthorpe, Jiaqi Yan, Vikram Sethi (Thanks!)
> - Updated the check to prevent multiple registration to the same PFN
> range using interval_tree_iter_first. Thanks Shameer Kolothum for the
> suggestion.
> - Removed the callback function in the nvgrace-gpu requiring tracking of
> poisoned PFN as it isn't required anymore.

Hi Ankit,

I get that for nvgrace-gpu driver, you removed pfn_address_space_ops
because there is no need to unmap poisoned HBM page.

What about the nvgrace-egm driver? Now that you removed the
pfn_address_space_ops callback from pfn_address_space in [1], how can
nvgrace-egm driver know the poisoned EGM pages at runtime?

I expect the functionality to return retired pages should also include
runtime poisoned pages, which are not in the list queried from
egm-retired-pages-data-base during initialization. Or maybe my
expection is wrong/obsolete?

[1] https://lore.kernel.org/linux-mm/20230920140210.12663-2-ankita@nvidia.com
[2] https://lore.kernel.org/kvm/20250904040828.319452-12-ankita@nvidia.com

> - Introduced seperate collect_procs_pfn function to collect the list of
> processes mapping to the poisoned PFN.
>
> v1 -> v2
> - Change poisoned page tracking from bitmap to hashtable.
> - Addressed miscellaneous comments in v1.
>
> Link: https://lore.kernel.org/all/20240826204353.2228736-1-peterx@redhat.com/ [1]
> Link: https://lore.kernel.org/all/20240220115055.23546-1-ankita@nvidia.com/ [2]
>
> Ankit Agrawal (3):
>   mm: Change ghes code to allow poison of non-struct pfn
>   mm: handle poisoning of pfn without struct pages
>   vfio/nvgrace-gpu: register device memory for poison handling
>
>  MAINTAINERS                         |   1 +
>  drivers/acpi/apei/ghes.c            |   6 --
>  drivers/vfio/pci/nvgrace-gpu/main.c |  45 ++++++++-
>  include/linux/memory-failure.h      |  17 ++++
>  include/linux/mm.h                  |   1 +
>  include/ras/ras_event.h             |   1 +
>  mm/Kconfig                          |   1 +
>  mm/memory-failure.c                 | 145 +++++++++++++++++++++++++++-
>  8 files changed, 209 insertions(+), 8 deletions(-)
>  create mode 100644 include/linux/memory-failure.h
>
> --
> 2.34.1
>
>

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