Re: [PATCH v3 2/2] ACPI: APEI: handle synchronous exceptions in task work

[Shuai Xue <xueshuai@linux.alibaba.com>]

On 2023/4/6 PM8:39, Xiaofei Tan wrote:
> Hi Shuai,
> 
> Thanks for your this effort, and it's great.
> Some comments below.
> 
> 在 2023/3/17 15:24, 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:
>>
>> - task work for synchronous errors.
>> - and workqueue for asynchronous errors.
>>
>> Then for 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>
>> ---
>>   drivers/acpi/apei/ghes.c | 114 ++++++++++++++++++++++-----------------
>>   include/acpi/ghes.h      |   3 --
>>   mm/memory-failure.c      |  13 -----
>>   3 files changed, 64 insertions(+), 66 deletions(-)
>>
>> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
>> index cccd96596efe..1901ee3498c4 100644
>> --- a/drivers/acpi/apei/ghes.c
>> +++ b/drivers/acpi/apei/ghes.c
>> @@ -452,45 +452,79 @@ 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)
>> +static void 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;
>> +        return;
>>         pfn = PHYS_PFN(physical_addr);
>>       if (!pfn_valid(pfn) && !arch_is_platform_page(physical_addr)) {
>>           pr_warn_ratelimited(FW_WARN GHES_PFX
>>           "Invalid address in generic error data: %#llx\n",
>>           physical_addr);
>> -        return false;
>> +        return;
> 
> For synchronous errors, we need send SIGBUS to the current task if not recovered,
> as the behavior of this patch  in the function memory_failure_cb().
> Such abnormal branches should also be taken as not recovered.

You are right. Thank you for pointing this out. I overlooked the abnormal
branches. To sum up, there are three cases:

- 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.

As you commented, abnormal branches case should also be send SIGBUS, I will
handle it in ghes_proc_in_irq() if no work (task work or workqueue work) is
queued.

Best Regards,
Shuai

> 
> 
>> +    }
>> +
>> +    if (flags == MF_ACTION_REQUIRED && current->mm) {
>> +        twcb = kmalloc(sizeof(*twcb), GFP_ATOMIC);
>> +        if (!twcb)
>> +            return;
> 
> It's the same here.
> 
> 
>> +
>> +        twcb->pfn = pfn;
>> +        twcb->flags = flags;
>> +        init_task_work(&twcb->twork, memory_failure_cb);
>> +        task_work_add(current, &twcb->twork, TWA_RESUME);
>> +        return;
>>       }
>>         memory_failure_queue(pfn, flags);
>> -    return true;
>>   }
>>   -static bool ghes_handle_memory_failure(struct acpi_hest_generic_data *gdata,
>> +static void ghes_handle_memory_failure(struct acpi_hest_generic_data *gdata,
>>                          int sev, bool sync)
>>   {
>>       int flags = -1;
>> @@ -498,7 +532,7 @@ static bool ghes_handle_memory_failure(struct acpi_hest_generic_data *gdata,
>>       struct cper_sec_mem_err *mem_err = acpi_hest_get_payload(gdata);
>>         if (!(mem_err->validation_bits & CPER_MEM_VALID_PA))
>> -        return false;
>> +        return;
> 
> and here.
> 
> 
>>         /* iff following two events can be handled properly by now */
>>       if (sec_sev == GHES_SEV_CORRECTED &&
>> @@ -508,16 +542,15 @@ static bool ghes_handle_memory_failure(struct acpi_hest_generic_data *gdata,
>>           flags = sync ? MF_ACTION_REQUIRED : 0;
>>         if (flags != -1)
>> -        return ghes_do_memory_failure(mem_err->physical_addr, flags);
>> +        ghes_do_memory_failure(mem_err->physical_addr, flags);
>>   -    return false;
>> +    return;
>>   }
>>   -static bool ghes_handle_arm_hw_error(struct acpi_hest_generic_data *gdata,
>> +static void ghes_handle_arm_hw_error(struct acpi_hest_generic_data *gdata,
>>                          int sev, bool sync)
>>   {
>>       struct cper_sec_proc_arm *err = acpi_hest_get_payload(gdata);
>> -    bool queued = false;
>>       int sec_sev, i;
>>       char *p;
>>       int flags = sync ? MF_ACTION_REQUIRED : 0;
>> @@ -526,7 +559,7 @@ static bool ghes_handle_arm_hw_error(struct acpi_hest_generic_data *gdata,
>>         sec_sev = ghes_severity(gdata->error_severity);
>>       if (sev != GHES_SEV_RECOVERABLE || sec_sev != GHES_SEV_RECOVERABLE)
>> -        return false;
>> +        return;
> 
> and here.
> 
> 
>>         p = (char *)(err + 1);
>>       for (i = 0; i < err->err_info_num; i++) {
>> @@ -542,7 +575,7 @@ static bool ghes_handle_arm_hw_error(struct acpi_hest_generic_data *gdata,
>>            * and don't filter out 'corrected' error here.
>>            */
>>           if (is_cache && has_pa) {
>> -            queued = ghes_do_memory_failure(err_info->physical_fault_addr, flags);
>> +            ghes_do_memory_failure(err_info->physical_fault_addr, flags);
>>               p += err_info->length;
>>               continue;
>>           }
>> @@ -555,8 +588,6 @@ static bool ghes_handle_arm_hw_error(struct acpi_hest_generic_data *gdata,
>>                       error_type);
>>           p += err_info->length;
>>       }
> 
> and here, for the case that memory failure is not done, as PA is invalid.
> 
> 
>> -
>> -    return queued;
>>   }
>>     /*
>> @@ -654,7 +685,7 @@ static void ghes_defer_non_standard_event(struct acpi_hest_generic_data *gdata,
>>       schedule_work(&entry->work);
>>   }
>>   -static bool ghes_do_proc(struct ghes *ghes,
>> +static void ghes_do_proc(struct ghes *ghes,
>>                const struct acpi_hest_generic_status *estatus)
>>   {
>>       int sev, sec_sev;
>> @@ -662,7 +693,6 @@ static bool ghes_do_proc(struct ghes *ghes,
>>       guid_t *sec_type;
>>       const guid_t *fru_id = &guid_null;
>>       char *fru_text = "";
>> -    bool queued = false;
>>       bool sync = is_hest_sync_notify(ghes);
>>         sev = ghes_severity(estatus->error_severity);
>> @@ -681,13 +711,13 @@ static bool ghes_do_proc(struct ghes *ghes,
>>               atomic_notifier_call_chain(&ghes_report_chain, sev, mem_err);
>>                 arch_apei_report_mem_error(sev, mem_err);
>> -            queued = ghes_handle_memory_failure(gdata, sev, sync);
>> +            ghes_handle_memory_failure(gdata, sev, sync);
>>           }
>>           else if (guid_equal(sec_type, &CPER_SEC_PCIE)) {
>>               ghes_handle_aer(gdata);
>>           }
>>           else if (guid_equal(sec_type, &CPER_SEC_PROC_ARM)) {
>> -            queued = ghes_handle_arm_hw_error(gdata, sev, sync);
>> +            ghes_handle_arm_hw_error(gdata, sev, sync);
>>           } else {
>>               void *err = acpi_hest_get_payload(gdata);
>>   @@ -697,8 +727,6 @@ static bool ghes_do_proc(struct ghes *ghes,
>>                              gdata->error_data_length);
>>           }
>>       }
>> -
>> -    return queued;
>>   }
>>     static void __ghes_print_estatus(const char *pfx,
>> @@ -1000,9 +1028,7 @@ 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;
>>       u32 len, node_len;
>> -    int ret;
>>         llnode = llist_del_all(&ghes_estatus_llist);
>>       /*
>> @@ -1017,25 +1043,14 @@ 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);
>> +        ghes_do_proc(estatus_node->ghes, estatus);
>>           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 +1111,6 @@ 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;