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

[Xiaofei Tan <tanxiaofei@huawei.com>]

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@linux.alibaba.com>
>>> Tested-by: Ma Wupeng <mawupeng1@huawei.com>
>>> ---
>>>    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.

>
> 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;
> .