Message-ID: <75ec37d9-f0cd-4fd5-8f81-7bfdc8b4e3c6@linux.alibaba.com>
Date: Fri, 18 Oct 2024 08:08:58 +0800
From: Shuai Xue <xueshuai@...ux.alibaba.com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
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Subject: Re: [PATCH v14 3/3] ACPI: APEI: handle synchronous exceptions in task
 work



在 2024/10/17 17:56, Jonathan Cameron 写道:
> On Mon, 14 Oct 2024 16:42:40 +0800
> Shuai Xue <xueshuai@...ux.alibaba.com> wrote:
> 
>> 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
> 
> exception
> 
>> 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.
> memory_failure() to execute in kworker context.
> 
> (spell check in general)

Sorry for typos. Will fix it in next version. Thanks.
>>
>> 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:
> context, memory_failure():
> //No subject of the following two bullets otherwise.

I see, will fix it.
>>
>>    - 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
> 
> devmem accesses a poisoned page for which the HWPoison flag is 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
> 
> context
> 
>> EFAULT. So, devmem will access the posioned page and trigger an
>> excepction again, resulting in a synchronous error infinite loop. Such
> 
> exception

I see, will fix it.

> 
>> 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>
> One other trivial comment inline.
> 
> Whilst this also looks fine to me, there are others who (hopefully)
> understand these paths better than me.  With that said.
> 
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>

Thank you for valuable comments.

> 
>> ---
>>   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().
>>    */
>> -static void ghes_kick_task_work(struct callback_head *head)
>> +struct ghes_task_work {
>> +	struct callback_head twork;
>> +	u64 pfn;
>> +	int flags;
>> +};
>> +
>> +static void memory_failure_cb(struct callback_head *twork)
>>   {
>> -	struct acpi_hest_generic_status *estatus;
>> -	struct ghes_estatus_node *estatus_node;
>> -	u32 node_len;
>> +	struct ghes_task_work *twcb = container_of(twork, struct ghes_task_work, twork);
>> +	unsigned long pfn = twcb->pfn;
> 
> This local variable is not used consistently.  I'd just
> drop it in favor of always accessing via twcb->pfn

Agreed, will remove local pfn.


Best Regards,
Shuai

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