Re: [PATCH v4 2/2] ACPI: APEI: handle synchronous exceptions in task work

[Shuai Xue]

On 2023/4/11 PM5:02, Xiaofei Tan wrote:
> 
> 在 2023/4/11 11:16, Shuai Xue 写道:
>>
>> On 2023/4/11 AM9:44, Xiaofei Tan wrote:
>>> Hi Shuai,
>>>
>>> 在 2023/4/8 17:13, Shuai Xue 写道:
>>>> Hardware errors could be signaled by synchronous interrupt, e.g.  when an
>>>> error is detected by a background scrubber, or signaled by synchronous
>>>> exception, e.g. when an uncorrected error is consumed. Both synchronous and
>>>> asynchronous error are queued and handled by a dedicated kthread in
>>>> workqueue.
>>>>
>>>> commit 7f17b4a121d0 ("ACPI: APEI: Kick the memory_failure() queue for
>>>> synchronous errors") keep track of whether memory_failure() work was
>>>> queued, and make task_work pending to flush out the workqueue so that the
>>>> work for synchronous error is processed before returning to user-space.
>>>> The trick 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: the actual user-space process accessing the corrupt memory
>>>> location, but its memory failure work is handled in a kthread context, so
>>>> it will send SIGBUS with BUS_MCEERR_AO si_code to the actual user-space
>>>> process instead of BUS_MCEERR_AR in kill_proc().
>>>>
>>>> To this end, separate synchronous and asynchronous error handling into
>>>> different paths like X86 platform does:
>>>>
>>>> - valid synchronous errors: queue a task_work to synchronously send SIGBUS
>>>>     before ret_to_user.
>>>> - valid asynchronous errors: queue a work into workqueue to asynchronously
>>>>     handle memory failure.
>>>> - abnormal branches such as invalid PA, unexpected severity, no memory
>>>>     failure config support, invalid GUID section, OOM, etc.
>>>>
>>>> Then for valid synchronous errors, the current context in memory failure is
>>>> exactly belongs to the task consuming poison data and it will send SIBBUS
>>>> with proper si_code.
>>>>
>>>> Fixes: 7f17b4a121d0 ("ACPI: APEI: Kick the memory_failure() queue for synchronous errors")
>>>> Signed-off-by: Shuai Xue <xueshuai@xxxxxxxxxxxxxxxxx>
>>>> Tested-by: Ma Wupeng <mawupeng1@xxxxxxxxxx>
>>>> ---
>>>>    drivers/acpi/apei/ghes.c | 91 +++++++++++++++++++++++++++-------------
>>>>    include/acpi/ghes.h      |  3 --
>>>>    mm/memory-failure.c      | 13 ------
>>>>    3 files changed, 61 insertions(+), 46 deletions(-)
>>>>
>>>> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
>>>> index c479b85899f5..df5574264d1b 100644
>>>> --- a/drivers/acpi/apei/ghes.c
>>>> +++ b/drivers/acpi/apei/ghes.c
>>>> @@ -452,28 +452,51 @@ 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 sync_task_work - for synchronous RAS event
>>>> + *
>>>> + * @twork:                callback_head for task work
>>>> + * @pfn:                  page frame number of corrupted page
>>>> + * @flags:                fine tune action taken
>>>> + *
>>>> + * Structure to pass task work to be handled before
>>>> + * ret_to_user via task_work_add().
>>>>     */
>>>> -static void ghes_kick_task_work(struct callback_head *head)
>>>> +struct sync_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;
>>>> +    int ret;
>>>> +    struct sync_task_work *twcb =
>>>> +        container_of(twork, struct sync_task_work, twork);
>>>>    -    estatus_node = container_of(head, struct ghes_estatus_node, task_work);
>>>> -    if (IS_ENABLED(CONFIG_ACPI_APEI_MEMORY_FAILURE))
>>>> -        memory_failure_queue_kick(estatus_node->task_work_cpu);
>>>> +    ret = memory_failure(twcb->pfn, twcb->flags);
>>>> +    kfree(twcb);
>>>>    -    estatus = GHES_ESTATUS_FROM_NODE(estatus_node);
>>>> -    node_len = GHES_ESTATUS_NODE_LEN(cper_estatus_len(estatus));
>>>> -    gen_pool_free(ghes_estatus_pool, (unsigned long)estatus_node, node_len);
>>>> +    if (!ret)
>>>> +        return;
>>>> +
>>>> +    /*
>>>> +     * -EHWPOISON from memory_failure() means that it already sent SIGBUS
>>>> +     * to the current process with the proper error info,
>>>> +     * -EOPNOTSUPP means hwpoison_filter() filtered the error event,
>>>> +     *
>>>> +     * In both cases, no further processing is required.
>>>> +     */
>>>> +    if (ret == -EHWPOISON || ret == -EOPNOTSUPP)
>>>> +        return;
>>>> +
>>>> +    pr_err("Memory error not recovered");
>>>> +    force_sig(SIGBUS);
>>>>    }
>>>>      static bool ghes_do_memory_failure(u64 physical_addr, int flags)
>>>>    {
>>>>        unsigned long pfn;
>>>> +    struct sync_task_work *twcb;
>>>>          if (!IS_ENABLED(CONFIG_ACPI_APEI_MEMORY_FAILURE))
>>>>            return false;
>>>> @@ -486,6 +509,18 @@ static bool ghes_do_memory_failure(u64 physical_addr, int flags)
>>>>            return false;
>>>>        }
>>>>    +    if (flags == MF_ACTION_REQUIRED && current->mm) {
>>>> +        twcb = kmalloc(sizeof(*twcb), GFP_ATOMIC);
>>>> +        if (!twcb)
>>>> +            return false;
>>>> +
>>>> +        twcb->pfn = pfn;
>>>> +        twcb->flags = flags;
>>>> +        init_task_work(&twcb->twork, memory_failure_cb);
>>>> +        task_work_add(current, &twcb->twork, TWA_RESUME);
>>>> +        return true;
>>>> +    }
>>>> +
>>>>        memory_failure_queue(pfn, flags);
>>>>        return true;
>>>>    }
>>>> @@ -1000,9 +1035,8 @@ static void ghes_proc_in_irq(struct irq_work *irq_work)
>>>>        struct ghes_estatus_node *estatus_node;
>>>>        struct acpi_hest_generic *generic;
>>>>        struct acpi_hest_generic_status *estatus;
>>>> -    bool task_work_pending;
>>>> +    bool queued;
>>>>        u32 len, node_len;
>>>> -    int ret;
>>>>          llnode = llist_del_all(&ghes_estatus_llist);
>>>>        /*
>>>> @@ -1017,25 +1051,23 @@ static void ghes_proc_in_irq(struct irq_work *irq_work)
>>>>            estatus = GHES_ESTATUS_FROM_NODE(estatus_node);
>>>>            len = cper_estatus_len(estatus);
>>>>            node_len = GHES_ESTATUS_NODE_LEN(len);
>>>> -        task_work_pending = ghes_do_proc(estatus_node->ghes, estatus);
>>>> +
>>>> +        queued = ghes_do_proc(estatus_node->ghes, estatus);
>>>> +        /*
>>>> +         * No memory failure work is queued into work queue or task queue
>>>> +         * due to invalid PA, unexpected severity, OOM, etc, do a force
>>>> +         * kill.
>>>> +         */
>>>> +        if (!queued && current->mm)
>>>> +            force_sig(SIGBUS);
>>> The SIGBUS needs to be sent to the current only for synchronous exceptions. The judgment of this if statement does not guarantee this.
>>> Because the function ghes_proc_in_irq() is used for NMI, but NMI not only used for synchronous exception. One user SEA is synchronous
>>> exception, and some other users, such as SDEI, may be not synchronous exception.
>> Yes, you are right. I was going to handle abnormal cases for sync error
>> and async error. But SIGBUS sent to the current task for an asynchronous
>> error is totally wrong.
> 
> yes
> 
>> Is it safe to keep running when an asynchronous
>> error is not handled?
> 
> I think so. Corrupt data should not be consumed silently. It should be guaranteed by Chip platorm.
> If platform can't support this, it will still not be 100% safe even we panic the system here, once received
> uncorrected memory error section.
> 
> 
>>
>> And should we add some warning message in abnormal cases?
>> e.g pr_warn_ratelimited on invalid PA?
> 
> Do you mean here ? it is not needed, as ghes_print_estatus() has included this info.
> 
>     if (!(mem_err->validation_bits & CPER_MEM_VALID_PA))
>         return false;
> 
>>> You could transfer the sync flag out from ghes_do_proc() and judge it here, or change meaning of the ghes_do_proc() return value
>>> as if recovered.
>> I think we could get sync flag by estatus_node, e.g:
>>
>>     bool sync = is_hest_sync_notify(estatus_node->ghes);
> 
> It's ok for me.
> 
>>
>> Then the condition in if statement should be:
>>
>>     if (sync && !queued)
>>
>> I drop out current->mm from if statement. For sync errors, the current
>> is guaranteed to be in user task, kernel task for sync error will panic
>> in do_sea(), the caller of ghes_proc_in_irq(). For async errors, SIGBUS
>> to current is meaningless.
> 
> OK. It is correct for ARM SEA, if want to support more sync notify type,
> should consider in the future.


Thanks for confirmations. I will send a new version later.

Best Regards,
Shuai

> 
>>
>> Thank you.
>>
>> Best Regards,
>> Shuai
>>
>>>
>>>> +
>>>>            if (!ghes_estatus_cached(estatus)) {
>>>>                generic = estatus_node->generic;
>>>>                if (ghes_print_estatus(NULL, generic, estatus))
>>>>                    ghes_estatus_cache_add(generic, estatus);
>>>>            }
>>>> -
>>>> -        if (task_work_pending && current->mm) {
>>>> -            estatus_node->task_work.func = ghes_kick_task_work;
>>>> -            estatus_node->task_work_cpu = smp_processor_id();
>>>> -            ret = task_work_add(current, &estatus_node->task_work,
>>>> -                        TWA_RESUME);
>>>> -            if (ret)
>>>> -                estatus_node->task_work.func = NULL;
>>>> -        }
>>>> -
>>>> -        if (!estatus_node->task_work.func)
>>>> -            gen_pool_free(ghes_estatus_pool,
>>>> -                      (unsigned long)estatus_node, node_len);
>>>> +        gen_pool_free(ghes_estatus_pool, (unsigned long)estatus_node,
>>>> +                  node_len);
>>>>              llnode = next;
>>>>        }
>>>> @@ -1096,7 +1128,6 @@ static int ghes_in_nmi_queue_one_entry(struct ghes *ghes,
>>>>          estatus_node->ghes = ghes;
>>>>        estatus_node->generic = ghes->generic;
>>>> -    estatus_node->task_work.func = NULL;
>>>>        estatus = GHES_ESTATUS_FROM_NODE(estatus_node);
>>>>          if (__ghes_read_estatus(estatus, buf_paddr, fixmap_idx, len)) {
>>>> diff --git a/include/acpi/ghes.h b/include/acpi/ghes.h
>>>> index 3c8bba9f1114..e5e0c308d27f 100644
>>>> --- a/include/acpi/ghes.h
>>>> +++ b/include/acpi/ghes.h
>>>> @@ -35,9 +35,6 @@ struct ghes_estatus_node {
>>>>        struct llist_node llnode;
>>>>        struct acpi_hest_generic *generic;
>>>>        struct ghes *ghes;
>>>> -
>>>> -    int task_work_cpu;
>>>> -    struct callback_head task_work;
>>>>    };
>>>>      struct ghes_estatus_cache {
>>>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
>>>> index fae9baf3be16..6ea8c325acb3 100644
>>>> --- a/mm/memory-failure.c
>>>> +++ b/mm/memory-failure.c
>>>> @@ -2355,19 +2355,6 @@ static void memory_failure_work_func(struct work_struct *work)
>>>>        }
>>>>    }
>>>>    -/*
>>>> - * Process memory_failure work queued on the specified CPU.
>>>> - * Used to avoid return-to-userspace racing with the memory_failure workqueue.
>>>> - */
>>>> -void memory_failure_queue_kick(int cpu)
>>>> -{
>>>> -    struct memory_failure_cpu *mf_cpu;
>>>> -
>>>> -    mf_cpu = &per_cpu(memory_failure_cpu, cpu);
>>>> -    cancel_work_sync(&mf_cpu->work);
>>>> -    memory_failure_work_func(&mf_cpu->work);
>>>> -}
>>>> -
>>>>    static int __init memory_failure_init(void)
>>>>    {
>>>>        struct memory_failure_cpu *mf_cpu;
>> .