Re: [PATCH v5 2/2] ACPI: APEI: handle synchronous exceptions in task work

[Shuai Xue]

On 2023/4/11 PM10:28, Kefeng Wang wrote:
> 
> 
> On 2023/4/11 18:48, Shuai Xue wrote:
>> 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..4b70955e25f9 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,
> 
> This should be part of the comments of function memory_failure(),
> 
>> +     * -EOPNOTSUPP means hwpoison_filter() filtered the error event,
>> +     *
> and this part is already there
>> +     * In both cases, no further processing is required.
>> +     */
> so, after that, I think we could drop this comment, also the same comment in x86's kill_me_maybe().

Ok, I will add comments on return value of memory_failure() and drop both this
comment and that in kill_me_maybe() out.

> 
>> +    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, sync;
>>       u32 len, node_len;
>> -    int ret;
>>         llnode = llist_del_all(&ghes_estatus_llist);
>>       /*
>> @@ -1015,27 +1049,25 @@ static void ghes_proc_in_irq(struct irq_work *irq_work)
>>           estatus_node = llist_entry(llnode, struct ghes_estatus_node,
>>                          llnode);
>>           estatus = GHES_ESTATUS_FROM_NODE(estatus_node);
>> +        sync = is_hest_sync_notify(estatus_node->ghes);
>>           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) > +        /*
>> +         * If no memory failure work is queued for abnormal synchronous
>> +         * errors, do a force kill.
>> +         */
>> +        if (sync && !queued)
>> +            force_sig(SIGBUS);
> 
> It's better to move this part into function ghes_do_proc(), because there is already an is_hest_sync_notify(), and no need return value,
> so make ghes_do_proc() a void function, Apart from this,

Good idea. I will do this and send a new version.

> 
> Reviewed-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>

Thank you.

Cheers,
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;