Message-ID: <05a8d26b-b023-426f-879c-7d33be4a6406@linux.alibaba.com>
Date: Tue, 22 Oct 2024 09:11:37 +0800
From: Shuai Xue <xueshuai@...ux.alibaba.com>
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Subject: Re: [PATCH v14 3/3] ACPI: APEI: handle synchronous exceptions in task
 work

Hi, Jarkko,


在 2024/10/14 16:42, Shuai Xue 写道:
> The memory uncorrected error could be signaled by asynchronous interrupt
> (specifically, SPI in arm64 platform), e.g. when an error is detected by
> a background scrubber, or signaled by synchronous exception
> (specifically, data abort excepction in arm64 platform), e.g. when a CPU
> tries to access a poisoned cache line. 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:
> 
>    #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:
> 
>    # 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
> 
> 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 above two issues, queue memory_failure() as a task_work so that it runs in
> the context of the process that is actually consuming the poisoned data.
> 
> Signed-off-by: Shuai Xue <xueshuai@...ux.alibaba.com>
> Tested-by: Ma Wupeng <mawupeng1@...wei.com>
> Reviewed-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> Reviewed-by: Xiaofei Tan <tanxiaofei@...wei.com>
> Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
>   drivers/acpi/apei/ghes.c | 78 +++++++++++++++++++++++-----------------
>   include/acpi/ghes.h      |  3 --
>   include/linux/mm.h       |  1 -
>   mm/memory-failure.c      | 13 -------
>   4 files changed, 45 insertions(+), 50 deletions(-)
> 
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index f2ee28c44d7a..95e9520eb803 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -467,28 +467,42 @@ static void ghes_clear_estatus(struct ghes *ghes,
>   }
>   
>   /*
> - * Called as task_work before returning to user-space.
> - * Ensure any queued work has been done before we return to the context that
> - * triggered the notification.
> + * struct ghes_task_work - for synchronous RAS event
> + *
> + * @twork:                callback_head for task work
> + * @pfn:                  page frame number of corrupted page
> + * @flags:                work control flags
> + *
> + * Structure to pass task work to be handled before
> + * returning to user-space via task_work_add().
>    */


Do you have any futer comments about this patch? Any comments are
welcomed. If not, are you happy to explictly give the reveiwed-by tag?

Best Regard,
Shuai

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