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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Thu, 30 Mar 2023 11:52:55 +0200
Message-ID: <CAJZ5v0jTjvCOZ_HikgopbDeqv1xWGbbOkNrktTZEPNDtZWXskg@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>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>, tony.luck@intel.com,
        james.morse@arm.com, bp@alien8.de,
        Naoya Horiguchi <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 Thu, Mar 30, 2023 at 8:11 AM Shuai Xue <xueshuai@linux.alibaba.com> wrote:
>
>
> On 2023/3/21 AM2:03, Rafael J. Wysocki wrote:
> > 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.
>
> Gentle ping.

As already stated in this thread, this series requires reviews from
the designated APEI reviewers (Tony, Boris, James).

Thanks!