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References: <20221027042445.60108-1-xueshuai@linux.alibaba.com> <20230317072443.3189-1-xueshuai@linux.alibaba.com>
In-Reply-To: <20230317072443.3189-1-xueshuai@linux.alibaba.com>
From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Mon, 20 Mar 2023 19:03:14 +0100
Message-ID: <CAJZ5v0gXTbxP5VkNWY+UiXM9oiGmtQbnCsMrCW8n40TvQehcWA@mail.gmail.com>
Subject: Re: [PATCH v3 0/2] ACPI: APEI: handle synchronous exceptions with
 proper si_code
To:     Shuai Xue <xueshuai@linux.alibaba.com>, tony.luck@intel.com,
        james.morse@arm.com, bp@alien8.de
Cc:     naoya.horiguchi@nec.com, linux-acpi@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        justin.he@arm.com, akpm@linux-foundation.org, ardb@kernel.org,
        ashish.kalra@amd.com, baolin.wang@linux.alibaba.com,
        cuibixuan@linux.alibaba.com, dave.hansen@linux.intel.com,
        jarkko@kernel.org, lenb@kernel.org, linmiaohe@huawei.com,
        lvying6@huawei.com, xiexiuqi@huawei.com,
        zhuo.song@linux.alibaba.com
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On Fri, Mar 17, 2023 at 8:25 AM Shuai Xue <xueshuai@linux.alibaba.com> wrote:
>
> changes since v2 by addressing comments from Naoya:
> - rename mce_task_work to sync_task_work
> - drop ACPI_HEST_NOTIFY_MCE case in is_hest_sync_notify()
> - add steps to reproduce this problem in cover letter
> - Link: https://lore.kernel.org/lkml/1aa0ca90-d44c-aa99-1e2d-bd2ae610b088@linux.alibaba.com/T/#mb3dede6b7a6d189dc8de3cf9310071e38a192f8e
>
> changes since v1:
> - synchronous events by notify type
> - Link: https://lore.kernel.org/lkml/20221206153354.92394-3-xueshuai@linux.alibaba.com/
>
> Currently, both synchronous and asynchronous error are queued and handled
> by a dedicated kthread in workqueue. And Memory failure for synchronous
> error is synced by a cancel_work_sync trick which ensures that the
> corrupted page is unmapped and poisoned. And after returning to user-space,
> the task starts at current instruction which triggering a page fault in
> which kernel will send SIGBUS to current process due to VM_FAULT_HWPOISON.
>
> However, the memory failure recovery for hwpoison-aware mechanisms does not
> work as expected. For example, hwpoison-aware user-space processes like
> QEMU register their customized SIGBUS handler and enable early kill mode by
> seting PF_MCE_EARLY at initialization. Then the kernel will directy notify
> the process by sending a SIGBUS signal in memory failure with wrong
> si_code: BUS_MCEERR_AO si_code to the actual user-space process instead of
> BUS_MCEERR_AR.
>
> To address this problem:
>
> - PATCH 1 sets mf_flags as MF_ACTION_REQUIRED on synchronous events which
>   indicates error happened in current execution context
> - PATCH 2 separates synchronous error handling into task work so that the
>   current context in memory failure is exactly belongs to the task
>   consuming poison data.
>
> Then, kernel will send SIGBUS with proper si_code in kill_proc().
>
> Lv Ying and XiuQi also proposed to address similar problem and we discussed
> about new solution to add a new flag(acpi_hest_generic_data::flags bit 8) to
> distinguish synchronous event. [2][3] The UEFI community still has no response.
> After a deep dive into the SDEI TRM, the SDEI notification should be used for
> asynchronous error. As SDEI TRM[1] describes "the dispatcher can simulate an
> exception-like entry into the client, **with the client providing an additional
> asynchronous entry point similar to an interrupt entry point**". The client
> (kernel) lacks complete synchronous context, e.g. systeam register (ELR, ESR,
> etc). So notify type is enough to distinguish synchronous event.
>
> To reproduce this problem:
>
>         # STEP1: enable early kill mode
>         #sysctl -w vm.memory_failure_early_kill=1
>         vm.memory_failure_early_kill = 1
>
>         # STEP2: inject an UCE error and consume it to trigger a synchronous error
>         #einj_mem_uc single
>         0: single   vaddr = 0xffffb0d75400 paddr = 4092d55b400
>         injecting ...
>         triggering ...
>         signal 7 code 5 addr 0xffffb0d75000
>         page not present
>         Test passed
>
> The si_code (code 5) from einj_mem_uc indicates that it is BUS_MCEERR_AO error
> and it is not fact.
>
> After this patch set:
>
>         # STEP1: enable early kill mode
>         #sysctl -w vm.memory_failure_early_kill=1
>         vm.memory_failure_early_kill = 1
>
>         # STEP2: inject an UCE error and consume it to trigger a synchronous error
>         #einj_mem_uc single
>         0: single   vaddr = 0xffffb0d75400 paddr = 4092d55b400
>         injecting ...
>         triggering ...
>         signal 7 code 4 addr 0xffffb0d75000
>         page not present
>         Test passed
>
> The si_code (code 4) from einj_mem_uc indicates that it is BUS_MCEERR_AR error
> as we expected.
>
> [1] https://developer.arm.com/documentation/den0054/latest/
> [2] https://lore.kernel.org/linux-arm-kernel/20221205160043.57465-4-xiexiuqi@huawei.com/T/
> [3] https://lore.kernel.org/lkml/20221209095407.383211-1-lvying6@huawei.com/
>
> Shuai Xue (2):
>   ACPI: APEI: set memory failure flags as MF_ACTION_REQUIRED on
>     synchronous events
>   ACPI: APEI: handle synchronous exceptions in task work
>
>  drivers/acpi/apei/ghes.c | 135 ++++++++++++++++++++++++---------------
>  include/acpi/ghes.h      |   3 -
>  mm/memory-failure.c      |  13 ----
>  3 files changed, 83 insertions(+), 68 deletions(-)
>
> --

I really need the designated APEI reviewers to give their feedback on this.