Re: [PATCH v12 0/3] ACPI: APEI: handle synchronous errors in task work

Shuai Xue
2024-09-18T02:16:17Z

Hi, all,

Gentle ping.

Best Regards,
Shuai

在 2024/9/2 11:00, Shuai Xue 写道:
> ## Changes Log
>
> changes since v11:
> - rebase to Linux 6.11-rc6
> - fix grammer and typo in commit log (per Borislav)
> - remove `sync_` perfix of `sync_task_work` (per Borislav)
> - comments flags and description of `task_work` (per Borislav)
>
> changes since v10:
> - rebase to v6.8-rc2
>
> changes since v9:
> - split patch 2 to address exactly one issue in one patch (per Borislav)
> - rewrite commit log according to template (per Borislav)
> - pickup reviewed-by tag of patch 1 from James Morse
> - alloc and free twcb through gen_pool_{alloc, free) (Per James)
> - rewrite cover letter
>
> changes since v8:
> - remove the bug fix tag of patch 2 (per Jarkko Sakkinen)
> - remove the declaration of memory_failure_queue_kick (per Naoya Horiguchi)
> - rewrite the return value comments of memory_failure (per Naoya Horiguchi)
>
> changes since v7:
> - rebase to Linux v6.6-rc2 (no code changed)
> - rewritten the cover letter to explain the motivation of this patchset
>
> changes since v6:
> - add more explicty error message suggested by Xiaofei
> - pick up reviewed-by tag from Xiaofei
> - pick up internal reviewed-by tag from Baolin
>
> changes since v5 by addressing comments from Kefeng:
> - document return value of memory_failure()
> - drop redundant comments in call site of memory_failure()
> - make ghes_do_proc void and handle abnormal case within it
> - pick up reviewed-by tag from Kefeng Wang
>
> changes since v4 by addressing comments from Xiaofei:
> - do a force kill only for abnormal sync errors
>
> changes since v3 by addressing comments from Xiaofei:
> - do a force kill for abnormal memory failure error such as invalid PA,
> unexpected severity, OOM, etc
> - pcik up tested-by tag from Ma Wupeng
>
> 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
>
> changes since v1:
> - synchronous events by notify type
> - Link: https://lore.kernel.org/lkml/20221206153354.92394-3-xueshuai@linux.alibaba.com/
>
> ## Cover Letter
>
> There are two major types of uncorrected recoverable (UCR) errors :
>
> - Synchronous error: The error is detected and raised at the point of the
> consumption in the execution flow, e.g. when a CPU tries to access
> a poisoned cache line. The CPU will take a synchronous error exception
> such as Synchronous External Abort (SEA) on Arm64 and Machine Check
> Exception (MCE) on X86. OS requires to take action (for example, offline
> failure page/kill failure thread) to recover this uncorrectable error.
>
> - Asynchronous error: The error is detected out of processor execution
> context, e.g. when an error is detected by a background scrubber. Some data
> in the memory are corrupted. But the data have not been consumed. OS is
> optional to take action to recover this uncorrectable error.
>
> Currently, both synchronous and asynchronous error use
> memory_failure_queue() to schedule memory_failure() exectute in kworker
> context. As a result, when a user-space process is accessing a poisoned
> data, a data abort is taken and the memory_failure() is executed in the
> kworker context:
>
> - will send wrong si_code by SIGBUS signal in early_kill mode, and
> - can not kill the user-space in some cases resulting a synchronous
> error infinite loop
>
> Issue 1: send wrong si_code in early_kill mode
>
> Since commit a70297d22132 ("ACPI: APEI: set memory failure flags as
> MF_ACTION_REQUIRED on synchronous events")', the flag MF_ACTION_REQUIRED
> could be used to determine whether a synchronous exception occurs on
> ARM64 platform. When a synchronous exception is detected, the kernel is
> expected to terminate the current process which has accessed poisoned
> page. This is done by sending a SIGBUS signal with an error code
> BUS_MCEERR_AR, indicating an action-required machine check error on
> read.
>
> However, when kill_proc() is called to terminate the processes who have
> the poisoned page mapped, it sends the incorrect SIGBUS error code
> BUS_MCEERR_AO because the context in which it operates is not the one
> where the error was triggered.
>
> 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.
>
> To fix it, queue memory_failure() as a task_work so that it runs in
> the context of the process that is actually consuming the poisoned data.
>
> 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.
>
> Issue 2: a synchronous error infinite loop due to memory_failure() failed
>
> If a user-space process, e.g. devmem, a poisoned page which has been set
> HWPosion flag, kill_accessing_process() is called to send SIGBUS to the
> current processs with error info. Because the memory_failure() is
> executed in the kworker contex, it will just do nothing but return
> EFAULT. So, devmem will access the posioned page and trigger an
> excepction again, resulting in a synchronous error infinite loop. Such
> loop may cause platform firmware to exceed some threshold and reboot
> when Linux could have recovered from this error.
>
> To reproduce this problem:
>
> # STEP 1: inject an UCE error, and kernel will set HWPosion flag for related page
> #einj_mem_uc single
> 0: single vaddr = 0xffffb0d75400 paddr = 4092d55b400
> injecting ...
> triggering ...
> signal 7 code 4 addr 0xffffb0d75000
> page not present
> Test passed
>
> # STEP 2: access the same page and it will trigger a synchronous error infinite loop
> devmem 0x4092d55b400
>
> To fix it, if memory_failure() failed, perform a force kill to current process.
>
> Issue 3: a synchronous error infinite loop due to no memory_failure() queued
>
> No memory_failure() work is queued unless all bellow preconditions check passed:
>
> - `if (!(mem_err->validation_bits & CPER_MEM_VALID_PA))` in ghes_handle_memory_failure()
> - `if (flags == -1)` in ghes_handle_memory_failure()
> - `if (!IS_ENABLED(CONFIG_ACPI_APEI_MEMORY_FAILURE))` in ghes_do_memory_failure()
> - `if (!pfn_valid(pfn) && !arch_is_platform_page(physical_addr)) ` in ghes_do_memory_failure()
>
> If the preconditions are not passed, the user-space process will trigger SEA again.
> This loop can potentially exceed the platform firmware threshold or even
> trigger a kernel hard lockup, leading to a system reboot.
>
> To fix it, if no memory_failure() queued, perform a force kill to current process.
>
> And the the memory errors triggered in kernel-mode[5], also relies on this
> patchset to kill the failure thread.
>
> Lv Ying and XiuQi from Huawei also proposed to address similar problem[2][4].
> Acknowledge to discussion with them.
>
> [1] Add ARMv8 RAS virtualization support in QEMU https://patchew.org/QEMU/20200512030609.19593-1-gengdongjiu@huawei.com/
> [2] https://lore.kernel.org/lkml/20221205115111.131568-3-lvying6@huawei.com/
> [3] https://lkml.kernel.org/r/20220914064935.7851-1-xueshuai@linux.alibaba.com
> [4] https://lore.kernel.org/lkml/20221209095407.383211-1-lvying6@huawei.com/
> [5] https://patchwork.kernel.org/project/linux-arm-kernel/cover/20240528085915.1955987-1-tongtiangen@huawei.com/
>
> Shuai Xue (3):
> ACPI: APEI: send SIGBUS to current task if synchronous memory error
> not recovered
> mm: memory-failure: move return value documentation to function
> declaration
> ACPI: APEI: handle synchronous exceptions in task work
>
> arch/x86/kernel/cpu/mce/core.c | 7 ---
> drivers/acpi/apei/ghes.c | 86 +++++++++++++++++++++-------------
> include/acpi/ghes.h | 3 --
> include/linux/mm.h | 1 -
> mm/memory-failure.c | 22 +++------
> 5 files changed, 60 insertions(+), 59 deletions(-)
>