Message-ID: <c779d666-4937-e2dc-2d52-da0e49d5d1ac@linux.alibaba.com>
Date:   Wed, 7 Dec 2022 18:57:32 +0800
From:   Shuai Xue <xueshuai@...ux.alibaba.com>
To:     Lv Ying <lvying6@...wei.com>, rafael@...nel.org, lenb@...nel.org,
        james.morse@....com, tony.luck@...el.com, bp@...en8.de,
        naoya.horiguchi@....com, linmiaohe@...wei.com,
        akpm@...ux-foundation.org, ashish.kalra@....com
Cc:     xiezhipeng1@...wei.com, wangkefeng.wang@...wei.com,
        xiexiuqi@...wei.com, tanxiaofei@...wei.com,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Bixuan Cui <cuibixuan@...ux.alibaba.com>,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        yingwen.cyw@...baba-inc.com
Subject: Re: [RFC 1/2] ACPI: APEI: Make memory_failure() triggered by
 synchronization errors execute in the current context



在 2022/12/5 PM7:51, Lv Ying 写道:
> The memory uncorrected error which is detected by an external component and
> notified via an IRQ, can be called asynchronization error. If an error is
> detected as a result of user-space process accessing a corrupt memory
> location, the CPU may take an abort. On arm64 this is a
> 'synchronous external abort', and on a firmware first system it is notified
> via NOTIFY_SEA, this can be called synchronization error.
> 
> Currently, synchronization error and asynchronization error both use
> memory_failure_queue to schedule memory_failure() exectute in kworker
> context. Commit 7f17b4a121d0 ("ACPI: APEI: Kick the memory_failure() queue
> for synchronous errors") make task_work pending to flush out the queue,
> cancel_work_sync() in memory_failure_queue_kick() will make
> memory_failure() exectute in kworker context first which will get
> synchronization error info from kfifo, so task_work later will get nothing
> from kfifo which doesn't work as expected. Even worse, synchronization
> error notification has NMI like properties, (it can interrupt IRQ-masked
> code), task_work may get wrong kfifo entry from interrupted
> asynchronization error which is notified by IRQ.
> 
> Since the memory_failure() triggered by a synchronous exception is
> executed in the kworker context, the early_kill mode of memory_failure()
> will send wrong si_code by SIGBUS signal: current process is kworker
> thread, the actual user-space process accessing the corrupt memory location
> will be collected by find_early_kill_thread(), and then send SIGBUS with
> BUS_MCEERR_AO si_code to the actual user-space process instead of
> BUS_MCEERR_AR. The machine-manager(kvm) use the si_code: BUS_MCEERR_AO for
> 'action optional' early notifications, and BUS_MCEERR_AR for
> 'action required' synchronous/late notifications.
> 
> Make memory_failure() triggered by synchronization errors execute in the
> current context, we do not need workqueue for synchronization error
> anymore, use task_work handle synchronization errors directly. Since,
> synchronization errors and asynchronization errors share the same kfifo,
> use MF_ACTION_REQUIRED flag to distinguish them. And the asynchronization
> error keeps the same as before.


Hi, Lv Ying,

Thank you for your great work.

We also encountered this problem in production environment, and tried to
solve it by dividing synchronous and asynchronous error handling into different
paths: task work for synchronous error and workqueue for asynchronous error.

The main challenge is how to distinguish synchronous errors in kernel first
mode through APEI, a related discussion is here.[1]

> @@ -978,14 +979,14 @@ 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);
> +		corruption_page_pending = ghes_do_proc(estatus_node->ghes, estatus, true);
>  		if (!ghes_estatus_cached(estatus)) {
>  			generic = estatus_node->generic;
>  			if (ghes_print_estatus(NULL, generic, estatus))
>  				ghes_estatus_cache_add(generic, estatus);
>  		}

In the case of your patch, it is inappropriate to assume that ghes_proc_in_irq() is only
called to handle synchronous error. Firmware could notify all synchronous and asynchronous
error signals to kernel through NMI notification, e.g. SDEI. In this case, asynchronous
error will be treated as synchronous error.

Our colleague Yingwen has submitted a proposal to extend acpi_hest_generic_data::flag (bit 8)
to indicate that the error is a synchronous[2]. Personally speaking, it is a more general
solution and completely solves the problem.


> Background:
>
> In ARM world, two type events (Sync/Async) from hardware IP need OS/VMM take different actions.
> Current CPER memory error record is not able to distinguish sync/async type event right now.
> Current OS/VMM need to take extra actions beyond CPER which is heavy burden to identify the
> two type events
>
> Sync event (e.g. CPU consume poisoned data) --> Firmware  -> CPER error log  --> OS/VMM take recovery action.
> Async event (e.g. Memory controller detect UE event)  --> Firmware  --> CPER error log  --> OS take page action.
>
>
> Proposal:
>
> - In section description Flags field(UEFI spec section N.2, add sync flag as below. OS/VMM
>  could depend on this flag to distinguish sync/async events.
> - Bit8 – sync flag; if set this flag indicates that this event record is synchronous(e.g.
>  cpu core consumes poison data, then cause instruction/data abort); if not set, this event record is asynchronous.
>
> Best regards,
> Yingwen Chen

A RFC patch set based on above proposal is here[3].

Thank you.

Best Regards,
Shuai


[1] https://lore.kernel.org/lkml/1aa0ca90-d44c-aa99-1e2d-bd2ae610b088@linux.alibaba.com/T/
[2] https://members.uefi.org/wg/uswg/mail/thread/9453
[3] https://lore.kernel.org/lkml/20221206153354.92394-2-xueshuai@linux.alibaba.com/


> 
> Signed-off-by: Lv Ying <lvying6@...wei.com>
> ---
>  drivers/acpi/apei/ghes.c | 27 ++++++++++++++-------------
>  mm/memory-failure.c      | 34 ++++++++++++++++++++++------------
>  2 files changed, 36 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index 9952f3a792ba..2ec71fc8a8dd 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -423,8 +423,8 @@ 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.
> + * Ensure any queued corrupt page in synchronous errors has been handled before
> + * we return to the user context that triggered the notification.
>   */
>  static void ghes_kick_task_work(struct callback_head *head)
>  {
> @@ -461,7 +461,7 @@ static bool ghes_do_memory_failure(u64 physical_addr, int flags)
>  }
>  
>  static bool ghes_handle_memory_failure(struct acpi_hest_generic_data *gdata,
> -				       int sev)
> +				       int sev, bool sync)
>  {
>  	int flags = -1;
>  	int sec_sev = ghes_severity(gdata->error_severity);
> @@ -475,7 +475,7 @@ static bool ghes_handle_memory_failure(struct acpi_hest_generic_data *gdata,
>  	    (gdata->flags & CPER_SEC_ERROR_THRESHOLD_EXCEEDED))
>  		flags = MF_SOFT_OFFLINE;
>  	if (sev == GHES_SEV_RECOVERABLE && sec_sev == GHES_SEV_RECOVERABLE)
> -		flags = 0;
> +		flags = sync ? MF_ACTION_REQUIRED : 0;
>  
>  	if (flags != -1)
>  		return ghes_do_memory_failure(mem_err->physical_addr, flags);
> @@ -483,7 +483,7 @@ static bool ghes_handle_memory_failure(struct acpi_hest_generic_data *gdata,
>  	return false;
>  }
>  
> -static bool ghes_handle_arm_hw_error(struct acpi_hest_generic_data *gdata, int sev)
> +static bool 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;
> @@ -510,7 +510,8 @@ static bool ghes_handle_arm_hw_error(struct acpi_hest_generic_data *gdata, int s
>  		 * and don't filter out 'corrected' error here.
>  		 */
>  		if (is_cache && has_pa) {
> -			queued = ghes_do_memory_failure(err_info->physical_fault_addr, 0);
> +			queued = ghes_do_memory_failure(err_info->physical_fault_addr,
> +					sync ? MF_ACTION_REQUIRED : 0);
>  			p += err_info->length;
>  			continue;
>  		}
> @@ -623,7 +624,7 @@ static void ghes_defer_non_standard_event(struct acpi_hest_generic_data *gdata,
>  }
>  
>  static bool ghes_do_proc(struct ghes *ghes,
> -			 const struct acpi_hest_generic_status *estatus)
> +			 const struct acpi_hest_generic_status *estatus, bool sync)
>  {
>  	int sev, sec_sev;
>  	struct acpi_hest_generic_data *gdata;
> @@ -648,13 +649,13 @@ static bool ghes_do_proc(struct ghes *ghes,
>  			ghes_edac_report_mem_error(sev, mem_err);
>  
>  			arch_apei_report_mem_error(sev, mem_err);
> -			queued = ghes_handle_memory_failure(gdata, sev);
> +			queued = 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);
> +			queued = ghes_handle_arm_hw_error(gdata, sev, sync);
>  		} else {
>  			void *err = acpi_hest_get_payload(gdata);
>  
> @@ -868,7 +869,7 @@ static int ghes_proc(struct ghes *ghes)
>  		if (ghes_print_estatus(NULL, ghes->generic, estatus))
>  			ghes_estatus_cache_add(ghes->generic, estatus);
>  	}
> -	ghes_do_proc(ghes, estatus);
> +	ghes_do_proc(ghes, estatus, false);
>  
>  out:
>  	ghes_clear_estatus(ghes, estatus, buf_paddr, FIX_APEI_GHES_IRQ);
> @@ -961,7 +962,7 @@ 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;
> +	bool corruption_page_pending;
>  	u32 len, node_len;
>  	int ret;
>  
> @@ -978,14 +979,14 @@ 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);
> +		corruption_page_pending = ghes_do_proc(estatus_node->ghes, estatus, true);
>  		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) {
> +		if (corruption_page_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,
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index bead6bccc7f2..3b6ac3694b8d 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -2204,7 +2204,11 @@ struct memory_failure_cpu {
>  static DEFINE_PER_CPU(struct memory_failure_cpu, memory_failure_cpu);
>  
>  /**
> - * memory_failure_queue - Schedule handling memory failure of a page.
> + * memory_failure_queue
> + * - Schedule handling memory failure of a page for asynchronous error, memory
> + *   failure page will be executed in kworker thread
> + * - put corrupt memory info into kfifo for synchronous error, task_work will
> + *   handle them before returning to the user
>   * @pfn: Page Number of the corrupted page
>   * @flags: Flags for memory failure handling
>   *
> @@ -2217,6 +2221,11 @@ static DEFINE_PER_CPU(struct memory_failure_cpu, memory_failure_cpu);
>   * happen outside the current execution context (e.g. when
>   * detected by a background scrubber)
>   *
> + * This function can also be used in synchronous errors which was detected as a
> + * result of user-space accessing a corrupt memory location, just put memory
> + * error info into kfifo, and then, task_work get and handle it in current
> + * execution context instead of scheduling kworker to handle it
> + *
>   * Can run in IRQ context.
>   */
>  void memory_failure_queue(unsigned long pfn, int flags)
> @@ -2230,9 +2239,10 @@ void memory_failure_queue(unsigned long pfn, int flags)
>  
>  	mf_cpu = &get_cpu_var(memory_failure_cpu);
>  	spin_lock_irqsave(&mf_cpu->lock, proc_flags);
> -	if (kfifo_put(&mf_cpu->fifo, entry))
> -		schedule_work_on(smp_processor_id(), &mf_cpu->work);
> -	else
> +	if (kfifo_put(&mf_cpu->fifo, entry)) {
> +		if (!(entry.flags & MF_ACTION_REQUIRED))
> +			schedule_work_on(smp_processor_id(), &mf_cpu->work);
> +	} else
>  		pr_err("buffer overflow when queuing memory failure at %#lx\n",
>  		       pfn);
>  	spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
> @@ -2240,7 +2250,7 @@ void memory_failure_queue(unsigned long pfn, int flags)
>  }
>  EXPORT_SYMBOL_GPL(memory_failure_queue);
>  
> -static void memory_failure_work_func(struct work_struct *work)
> +static void __memory_failure_work_func(struct work_struct *work, bool sync)
>  {
>  	struct memory_failure_cpu *mf_cpu;
>  	struct memory_failure_entry entry = { 0, };
> @@ -2256,22 +2266,22 @@ static void memory_failure_work_func(struct work_struct *work)
>  			break;
>  		if (entry.flags & MF_SOFT_OFFLINE)
>  			soft_offline_page(entry.pfn, entry.flags);
> -		else
> +		else if (!sync || (entry.flags & MF_ACTION_REQUIRED))
>  			memory_failure(entry.pfn, entry.flags);
>  	}
>  }
>  
> -/*
> - * Process memory_failure work queued on the specified CPU.
> - * Used to avoid return-to-userspace racing with the memory_failure workqueue.
> - */
> +static void memory_failure_work_func(struct work_struct *work)
> +{
> +	__memory_failure_work_func(work, false);
> +}
> +
>  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);
> +	__memory_failure_work_func(&mf_cpu->work, true);
>  }
>  
>  static int __init memory_failure_init(void)

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